 Using the Scan Tool State-of-Charge (SOC) PID has long been a staple for technicians to use as diagnostic data. The OEMs also have used it as a metric for determining the State-of-Health (SOH) of a Battery Pack (whether NiMH or Lithium). Unfortunately, NiMH battery controllers induce errors in the SOC% as a function of time and significant errors can result. These resulting errors can mislead a technician when evaluating the SOC or (more importantly) the SOH. The operation in a hybrid electric vehicle (HEV) is significantly dependent upon the SOH of the Battery Pack. Fuel Economy and vehicle performance are tied directly to Battery Pack SOH (and performance). MYTH: The scan tool PID for the SOC% (capacity) of a Hybrid Electric Vehicle (HEV) Nickel Metal Hydride battery module or pack can be trusted for accuracy on a used vehicle to determine actual capacity. FACT: The scan tool SOC% value on an aging HEV NiMH pack (e.g. starting at > 6 yrs in service) reflects what the battery controller “thinks” the state of charge is — not the actual SOC%. On a used vehicle, the two numbers often diverge by 10%, 20%, or more as the Battery Pack age increases. A technician who treats the PID as empirical will misdiagnose pack condition every time. Why the SOC% PID Drifts From Reality HEV battery controllers estimate SOC% using a combination of Coulomb counting, voltage-based lookup tables, and equivalent circuit models — all of which are calibrated against the assumptions of a new pack. As the pack ages, the physical properties of those models depend on shift, but the model does not. The result is a PID value that looks precise to three decimal places while being fundamentally wrong. Coulomb Counting and the Fixed-Denominator Problem Most HEV controllers integrate current flowing in and out of the pack over time, then divide by an assumed total capacity. As cells age and lose active material, actual pack capacity can fade by 20% or more — but the controller’s denominator doesn’t change. The SOC% calculation is therefore referenced against a capacity the pack no longer has. The PID overestimates remaining charge even when the math inside the controller is perfectly correct, because the number the math is divided by is wrong. Progressive Cell Imbalance HEV NiMH modules are series-connected. Manufacturing tolerances, thermal gradients across the pack, and uneven load exposure cause individual cells to age at different rates. A single weak cell will hit empty before the others are depleted, effectively stranding usable energy in the remaining cells. The controller, which typically monitors pack-level voltage rather than individual cell voltage, reports an average SOC% that tells the technician nothing about which cells are actually limiting the pack. Internal Resistance and Voltage Sag Internal resistance in an aging NiMH cell can climb to roughly 160% of its original value by end-of-life, driven primarily by corrosion of the negative metal hydride electrode. Under the high-current loads typical of HEV operation — regenerative braking, hard acceleration — this elevated resistance produces terminal voltage sag that the controller reads through its voltage-based lookup tables as low state of charge. The charge is actually there; the resistance is hiding it. The PID reports what the voltage says, not what the electrochemistry says. Hysteresis and Nonlinear Aging NiMH chemistry exhibits pronounced OCV hysteresis — open-circuit voltage at a given SOC differs by tens of millivolts depending on whether the pack was last charging or discharging, and this gap relaxes slowly over minutes to hours. Equivalent circuit models built into production HEV controllers simplify this behavior with static lookup tables. Those tables are accurate on a new pack at a reference temperature. On an aged pack operating across the thermal range a vehicle actually sees, the assumptions break down and the reported SOC% drifts accordingly. Sensor Drift and Error Accumulation Current and temperature sensors feeding the Coulomb counter carry small, persistent bias errors. Over thousands of charge and discharge cycles, these errors accumulate. HEV packs rarely see a full charge or full discharge — the controller operates in a narrow middle band — so the drift is seldom reset. After years of service, the cumulative error alone can render the PID value unreliable. Key Takeaways A capacity verdict based on scan tool SOC% is a guess dressed up as data. Genuine pack evaluation requires module-level voltage measurement under load, internal resistance testing per module, capacity verification with a reference load or stress test, and thermal imaging during a controlled discharge (if possible). Customer complaints tied to SOC% errors are poor fuel economy, poor performance on acceleration, and shuddering during acceleration or high load conditions. Examples of SOC% errors are when the Scan Tool provides an SOC% OF 61%, while the actual SOC% is less than 35% after being tested with off-board discharging equipment. Since the SOC% represents stored energy, this type of error would significantly effect vehicle performance. The scan tool SOC% PID is a control signal for the vehicle, not a diagnostic verdict for the technician. On a newer pack (i.e., <5 yrs) it is close enough to reality to be useful; an aged Battery Pack the SOC% error can be significant. Properly trained technicians verify SOC or SOH with instruments and validated testing processes, not assumptions. Diagnostic and testing techniques are covered across the EV Pro+ L1 through L8 curriculum, along with the diagnostic tool competencies that separate a technician who can read a PID from one who can evaluate a Battery Pack. Contact Us If you would like to discuss HEV / EV battery diagnostics or technician training, contact us at: 📩 [email protected] We welcome technical discussion. Technical References SAE International — Standards and Technical Articles SAE J1798 (2019). Recommended Practice for Performance Rating of Electric Vehicle Battery Modules. SAE International, Battery Standards Testing Committee. SAE J2288 (2008, reaffirmed). Life Cycle Testing of Electric Vehicle Battery Modules. SAE International. SAE J1715 (2014). Hybrid Electric Vehicle (HEV) and Electric Vehicle (EV) Terminology. SAE International. Andrushchak, V. (2025, Nov 17). Reducing SoC and SoH estimation errors: challenges and solutions in modern BMS. SAE International. sae.org/articles/2025/11/reducing-soc-soh-estimation-errors. Peer-Reviewed Literature Verbrugge, M., & Tate, E. (2004). Adaptive state of charge algorithm for nickel metal hydride batteries including hysteresis phenomena. Journal of Power Sources, 126(1–2), 236–249. (GM R&D; foundational SOC algorithm used in GM HEV programs.) Pan, Y.H., Srinivasan, V., & Wang, C.Y. (2002). An experimental and modeling study of isothermal charge/discharge behavior of commercial Ni-MH cells. Journal of Power Sources, 112(2), 298–306. Ota, H., et al. (2011). Modeling of voltage hysteresis and relaxation of HEV NiMH battery. Electrical Engineering in Japan, Wiley. Wu, B., & White, R.E. (2001). Modeling of a nickel-hydrogen cell phase reaction in the nickel active material. Journal of The Electrochemical Society, 148(6), A595–A609. Roscher, M.A., et al. (2011). OCV Hysteresis in Li-Ion Batteries including Two-Phase Transition Materials. International Journal of Electrochemistry, Wiley Online Library. MDPI Open-Access Journals Bertilsson, S., et al. (2021). Short-Term Impact of AC Harmonics on Aging of NiMH Batteries for Grid Storage Applications. Batteries, MDPI. (Identifies negative-electrode corrosion as the primary NiMH aging mechanism.) Zhang, S., et al. (2023). Capacity Degradation and Aging Mechanisms Evolution of Batteries under Different Operation Conditions. Energies, 16(10), 4232. MDPI. Madani, S.S., et al. (2025). A Comprehensive Review on Battery Lifetime Prediction and Aging Mechanism Analysis. Batteries, 11(4), 127. MDPI. U.S. Department of Energy / National Laboratory Sources Motloch, C.G., et al. (2002). Implications of NiMH Hysteresis on HEV Battery Testing and Performance. Proceedings of the 19th International Battery, Hybrid and Fuel Cell Electric Vehicle Symposium (EVS-19). Idaho National Engineering and Environmental Laboratory. PNGV Battery Test Manual (2001). DOE/ID-10597, Revision 3. U.S. Department of Energy, Partnership for a New Generation of Vehicles. IEEE Conference Proceedings Battery Pack Inconsistency Modeling and SOC Estimation Based on Improved Mean-Difference Model (2025). Proceedings of the 2025 37th Chinese Control and Decision Conference (CCDC), 16–19 May 2025. IEEE Xplore. Industry and Engineering References Battery Design LLC. SoC Estimation by Coulomb Counting. batterydesign.net technical reference library. Tang, X., Zhang, X., Koch, B., & Frisch, D. (2008). Modeling and estimation of nickel metal hydride battery hysteresis for SOC estimation. IEEE Prognostics and Health Management Conference Proceedings, 1–12. Disclaimer: This content is provided for general informational purposes only. It is based on publicly available data, standards, and published sources available at the time of release. It does not constitute advice of any kind. Information is provided as-is, without warranties, and no liability is assumed for actions taken based on this content.
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As electrified powertrains become more common, accurate testing of electric machines (motors and generators) is becoming a critical part of the diagnostic process. With the high cost of electric drive units and transmissions, determining the condition—or state of health (SOH)—of these components requires reliable and repeatable data. Despite this, simplified methods continue to circulate in the aftermarket, including the use of light bulbs to evaluate electric machine condition. While this approach may appear practical, it does not provide the level of insight required for accurate diagnostics. Myth vs. Fact MYTH Light bulbs can effectively be used to determine the conditions of EM SOH instead of buying “all of that expensive equipment” by merely observing the brightness and pulsing of light bulbs on each Phase while the EM is being rotated. FACT The SOH or condition of an EM cannot be determined merely by using light bulbs. The light bulb brightness and strength of pulse (while rotating the Rotor) is an extremely subjective test measurement that does not provide measurable test data that is based in a Recommended Practice or Standards. No such test can be found in any of the organizations that are responsible for developing contemporary Best Practices or Standards, and no Standards organization would ever consider it a viable test to determine SOH. Why Light Bulb Testing Falls Short Light bulb testing relies on visual interpretation—specifically brightness and pulsing—to draw conclusions about machine condition. The issue is not that the method produces no response, but that the response cannot be quantified or validated. Without measurable data, there is no way to:
What Light Bulb Testing Can Actually Do In very limited scenarios, light bulb testing may indicate the presence of a basic electrical condition. For example, when testing a permanent magnet machine with all three phases connected in series, a non-pulsing bulb may indicate an open circuit. However, even this use case is highly dependent on configuration. If phase coils are connected in parallel, the system may still produce a pulsing light even when a fault exists. Additionally, this method provides no useful information for induction machines or separately excited rotor systems. This reinforces an important distinction: detecting a simple fault is not the same as determining state of health. What Proper Electric Machine Testing Requires Accurate electric machine testing is based on measurable, multi-variable data. Determining SOH requires evaluating how the machine performs across multiple electrical and magnetic characteristics. Key measurements typically include:
Standards and Best Practices Electric machine testing is guided by established standards and recommended practices developed by industry organizations. These include:
The absence of light bulb testing from these standards is not an oversight—it reflects the method’s lack of diagnostic validity. Why This Myth Persists The appeal of light bulb testing is easy to understand. It is inexpensive, simple to perform, and does not require specialized equipment. However, this simplicity comes at the cost of accuracy. In environments where technical training or access to proper tools is limited, these types of methods can gain traction. Over time, they become accepted as “good enough,” even when they fail to provide reliable results. In professional settings, however, decisions must be based on data—not assumptions. The Cost of Inaccurate Testing Using incomplete or unreliable methods to evaluate electric machines can lead to a range of issues, including:
Final Takeaway Electric machine state of health cannot be determined using subjective methods such as light bulb testing. Accurate diagnostics require measurable, multi-variable data obtained through validated testing methods aligned with established standards. Reliable data leads to informed decisions, confident repairs, and better outcomes for both technicians and customers. Contact Us If you would like to review Electric Machine testing or test equipment, contact us at: 📩 [email protected] We welcome professional Electric Machine collaboration. References
This content is provided for general informational purposes only. It is based on publicly available data, standards, and published sources available at the time of release. It does not constitute advice of any kind. Information is provided as-is, without warranties, and no liability is assumed for actions taken based on this content.  As hybrid vehicles continue to be serviced across the industry, technicians often rely on familiar diagnostic approaches when evaluating battery systems. One of the most common methods is measuring terminal voltage with a voltmeter. While this approach works in many applications, it does not translate well to Nickel Metal Hydride (NiMH) battery systems. The behavior of these batteries introduces limitations that make voltage-based evaluation unreliable for both state of charge and overall condition. Myth vs. Fact MYTH A voltmeter can be used to determine a Hybrid Electric Vehicle Nickel Metal Hydride (NiMH) battery module or pack state of charge (SOC) or state of health (SOH) by measuring terminal voltage. FACT Voltage alone is not a reliable indicator of NiMH battery state of charge or state of health. Accurate SOC estimation requires advanced methods such as open-circuit voltage modeling or current tracking. For SOH, capacity testing and internal resistance measurement provide meaningful data. The flat discharge profile of NiMH batteries further limits the usefulness of voltage as a standalone measurement. Why NiMH Voltage Behaves Differently Unlike many battery chemistries, NiMH cells maintain a relatively stable voltage across a wide portion of their usable range. During normal operation, the voltage of an individual cell remains close to 1.2 volts for much of the charge cycle. Because this value changes very little between mid-level charge states, it does not provide enough detail to distinguish whether the battery is partially charged, near depletion, or somewhere in between. This characteristic alone makes voltage an unreliable indicator of state of charge without additional context. Limitations of Voltage for State of Charge Determining state of charge requires tracking how energy moves into and out of the battery over time. A single voltage reading captures only a momentary condition and does not reflect recent usage, load, or recovery behavior. To estimate SOC with any level of accuracy, systems rely on methods that incorporate multiple variables. These may include open-circuit voltage relationships, current flow tracking, and algorithm-based adjustments that account for how the battery responds during operation. Without these inputs, voltage alone lacks the resolution needed to provide a meaningful estimate. Why Voltage Falls Short for State of Health State of health reflects long-term battery condition, including its ability to store and deliver energy effectively. This is influenced by factors such as aging, internal resistance, and capacity loss. Voltage does not directly represent these characteristics. A degraded battery can still display normal voltage levels while experiencing reduced capacity or increased resistance under load. To evaluate condition accurately, technicians must look beyond voltage and use methods designed to measure performance, not just potential. What Actually Indicates Battery Condition Reliable assessment of a NiMH battery depends on tests that measure how the battery performs, not just what it reads. Capacity testing provides insight into how much energy the battery can store relative to its original specification. Internal resistance measurement helps identify how efficiently that energy can be delivered. Together, these approaches offer a far more accurate picture of battery condition than voltage alone. How Modern Systems Handle Battery Estimation Hybrid vehicles account for these limitations through their battery management systems. Instead of relying on voltage as a primary indicator, these systems use a combination of inputs to calculate state of charge and monitor performance. By continuously tracking current, temperature, and system behavior, the vehicle is able to make more accurate estimations than a single measurement could provide. This reinforces an important point for technicians: the system itself does not rely on voltage alone, and neither should the diagnostic process. Practical Implications for Technicians Relying solely on voltage when evaluating NiMH batteries can lead to incorrect conclusions about both charge level and overall condition. This can affect diagnostic decisions and may result in unnecessary or incomplete repairs. Understanding the limitations of voltage-based testing allows technicians to approach battery diagnostics with greater accuracy and confidence. Using the correct methods ensures that evaluations reflect actual performance rather than assumptions based on incomplete data. Final Takeaway Voltage alone cannot reliably determine the state of charge or state of health of a NiMH battery. Due to the battery’s discharge characteristics and overall behavior, accurate diagnostics require methods that measure capacity, resistance, and system performance over time. Recognizing these limitations is essential for making informed service decisions when working with hybrid battery systems. Contact Us If you would like to discuss EV battery diagnostics or technician training, contact us at: 📩 [email protected] We welcome technical discussion. References
Disclaimer: This content is provided for general informational purposes only. It is based on publicly available data, standards, and published sources available at the time of release. It does not constitute advice of any kind. Information is provided as-is, without warranties, and no liability is assumed for actions taken based on this content.  As electric vehicles become more common in service bays, technicians are adapting to new procedures and safety considerations. One area that continues to create confusion is what actually happens after the manual service disconnect is removed.
A common assumption is that once the disconnect is pulled, the vehicle is safe to work on. While this step is critical, it does not fully de-energize the system. Understanding what the service disconnect does—and what it does not do—is essential for safe and accurate EV service. Myth vs. Fact MYTH Once the manual service disconnect is removed, the vehicle is safe to perform work. FACT Removing the service disconnect isolates the high-voltage battery, but it does not eliminate all stored energy. Capacitors and other circuits may remain energized for a period of time. Proper disabling procedures require OEM-specified wait times, 12-volt system control, and verification of zero voltage before service begins. What the Service Disconnect Actually Does The manual service disconnect is designed to separate the high-voltage battery from the rest of the vehicle’s electrical system. This isolation is an important safety step, particularly when preparing a vehicle for service or diagnostics. However, isolation is not the same as de-energization. Even after the battery is disconnected, portions of the system can remain electrically active. The disconnect prevents additional energy from being supplied, but it does not remove energy that is already stored within the system. Why Energy Can Still Be Present Electric vehicles contain components that are specifically designed to store electrical energy. Among the most important of these are capacitors, which are commonly found in power electronics such as inverters and converters. These components allow the system to operate efficiently, but they also introduce a delay between disconnecting the battery and achieving a fully de-energized state. After the service disconnect is removed, stored energy within these components must dissipate. This process is not instantaneous and varies depending on the vehicle design and system configuration. During this period, high-voltage potential may still be present—even though the battery has been isolated. How Long Does Stored Energy Remain? The amount of time required for stored energy to dissipate is not universal. It is defined by the vehicle manufacturer and can vary from one platform to another. In many cases, OEM service procedures specify a required wait time after disconnecting the battery. This allows internal components, including capacitors, to discharge to a safe level before any work is performed. Assuming the system is safe immediately after removing the disconnect can create unnecessary risk. Following the specified wait time is a critical part of the process. What Proper De-Energizing Requires Making an EV safe to work on is a multi-step process, not a single action. In addition to removing the service disconnect, technicians must follow OEM-defined procedures that typically include managing the 12-volt system, allowing sufficient time for stored energy to dissipate, and verifying that voltage is no longer present. Verification is especially important. Even after completing the required steps, technicians should confirm zero voltage using properly rated test equipment before beginning work. This approach removes uncertainty and ensures that the system is truly safe. Why Assumptions Create Risk One of the most common safety issues in EV service is not a lack of knowledge, but a false sense of security. Because the service disconnect is a visible and deliberate action, it can create the impression that the system has been fully disabled. In reality, the presence of stored energy means that risk can still exist. Skipping wait times or failing to verify voltage introduces the possibility of electrical shock or unintended system interaction. These risks are avoidable when proper procedures are followed. A Shift in How Safety Is Defined Working on electric vehicles requires a different approach to safety than traditional internal combustion systems. In conventional vehicles, disconnecting the power source typically removes most immediate risk. In EVs, however, energy storage and system design require a more deliberate process. Safety is no longer defined by a single step. It is defined by understanding the system, following procedures, and confirming conditions before beginning work. Final Takeaway Removing the service disconnect is an important step in EV service, but it does not make the vehicle immediately safe to work on. Stored energy can remain in the system, and proper procedures must be followed to ensure full de-energization. This includes allowing for OEM-specified wait times and verifying zero voltage before service begins. Service disconnect removal is only one step in making an EV safe to perform work. Contact Us If you would like to discuss EV safety procedures or technician training, contact us at: 📩 [email protected] We welcome technical discussion. References: OEM EV service manuals SAE J2990 Disclaimer: This content is provided for general informational purposes only. It is based on publicly available data, standards, and published sources available at the time of release. It does not constitute advice of any kind. Information is provided as-is, without warranties, and no liability is assumed for actions taken based on this content.  Why Meter Ratings Matter More Than Ever
As electric vehicles continue to enter service bays, technicians are encountering a new set of challenges—not just in diagnostics, but in tool selection and safety. One of the most overlooked risks in EV service isn’t a lack of knowledge—it’s the assumption that existing tools are sufficient for high-voltage work. In many cases, they’re not. Myth vs. Fact MYTH When working on high-voltage systems, test equipment does not need a CAT III/1000V rating. FACT High-voltage EV systems can produce energy levels and transient conditions that require CAT III/1000V rated test equipment. Using under-rated meters increases the risk of equipment failure, inaccurate measurements, and potential safety hazards. What CAT Ratings Actually Mean Measurement category (CAT) ratings are not arbitrary labels—they are safety classifications that define how much electrical energy a piece of test equipment can safely withstand. In simple terms, CAT ratings account for:
A CAT I or CAT II meter may function in low-energy environments, but it is not designed to handle the energy levels present in high-voltage vehicle systems. Why EV Systems Require CAT III/1000V Equipment Electric vehicles operate with high-voltage systems that typically range from 300V to 800V, with the potential for significant transient energy during operation. These systems include:
CAT III/1000V rated meters are specifically built to:
The Risk of Using Under-Rated Equipment Using a meter that is not properly rated for EV work introduces multiple layers of risk. 1. Equipment Failure Meters that are not designed for high-energy environments can fail when exposed to conditions beyond their rating. This may result in:
2. Increased Shock Hazard Improperly rated equipment may not provide adequate protection against electrical faults. In high-voltage systems, this increases the risk of:
3. Inaccurate Readings Even if a lower-rated meter appears to function, it may not provide reliable data in high-energy environments. This can lead to:
Why This Misconception Happens Many technicians transition into EV service using the tools they are already familiar with from internal combustion engine (ICE) diagnostics. In traditional automotive systems:
Because of this, CAT I or CAT II meters are often sufficient. However, EV systems operate under completely different conditions. Applying the same assumptions to high-voltage systems creates a gap between what feels acceptable and what is actually safe. Standards That Define Safe Testing Practices The requirement for properly rated equipment is not based on preference—it is grounded in established safety standards. These include:
For technicians, they reinforce a critical principle: The tool must match the environment. The Shift in Technician Responsibility EV service is not just about learning new systems—it requires a shift in how technicians approach safety and diagnostics. This includes:
What Shops Should Be Evaluating Right Now As EVs become more common, shops should take a proactive approach to equipment readiness. Key questions include:
Final Takeaway Not all test equipment is suitable for EV diagnostics. High-voltage systems require tools that are specifically rated to handle the energy levels and conditions present in these environments. Using under-rated meters introduces unnecessary risk—to the equipment, the accuracy of the diagnosis, and most importantly, the technician. As EV adoption continues to grow, proper tool selection is no longer optional—it is essential. Contact Us If you would like to discuss EV safety procedures, test equipment selection, or technician training, contact us at: 📩 [email protected] We welcome technical discussion. References: IEC 61010-1, IEC 61010-2-030, UL 61010-1, NFPA 70E, ISO 6469-3:2021 Disclaimer: This content is provided for general informational purposes only. It is based on publicly available data, standards, and published sources available at the time of release. It does not constitute advice of any kind. Information is provided as-is, without warranties, and no liability is assumed for actions taken based on this content. Understanding Isolation Testing in Electric Vehicles.  MYTH
When performing an isolation test, the insulation meter should always be set to the highest testing voltage (1000 V or greater). FACT Insulation test voltage must be selected based on system voltage and OEM requirements. For many 300–400 V EV battery systems, 500 V is the specified test voltage. Using unnecessarily high voltages, such as 1000 V, can over-stress insulation or sensitive electronic components. Proper testing should follow OEM procedures developed in alignment with IEEE and IEC standards. As electric vehicle adoption continues to grow, so does the need for accurate and safe diagnostic procedures. One area that often creates confusion among technicians is insulation resistance testing, commonly referred to as isolation testing. A common misconception is that when performing an isolation test, the insulation meter should always be set to the highest available voltage—typically 1000 V or greater—to ensure accurate results. At first glance, this approach may seem logical. Higher voltage might appear to provide a more thorough test. However, in the context of EV systems, this assumption can lead to inaccurate results and, in some cases, unintended component stress. The reality is much more precise: Isolation testing is not about maximum voltage—it’s about using the correct voltage for the system being tested. What Is Isolation Testing and Why It Matters Isolation testing is used to evaluate the integrity of insulation between high-voltage components and the vehicle chassis. In EV and hybrid systems, this is critical for both safety and performance. Proper insulation ensures:
Where the “Higher Voltage Is Better” Myth Comes From The idea of using the highest possible test voltage often stems from traditional insulation testing practices in industrial or legacy electrical systems. In those contexts, higher test voltages are sometimes used to stress insulation and identify weaknesses. However, EV systems are not designed in the same way. Modern electric vehicles contain:
How Test Voltage Should Actually Be Selected In EV applications, insulation test voltage must be selected based on two key factors: 1. System Voltage The nominal voltage of the high-voltage system plays a primary role in determining the correct test level. For many EV battery systems operating in the 300–400 V range, the appropriate insulation test voltage is typically: 500 V This provides sufficient stress to evaluate insulation integrity without exceeding design limitations. 2. OEM Requirements and Procedures Perhaps more important than system voltage is adherence to OEM service information. Vehicle manufacturers define testing procedures based on:
Following OEM guidance ensures:
The Risk of Using Excessive Test Voltage Setting an insulation tester to 1000 V or higher when it is not required can have unintended consequences. Over-stressing Insulation: Insulation systems in EV components are designed for specific voltage ranges. Applying excessive test voltage can place unnecessary stress on insulation materials, potentially accelerating wear or degradation over time. Impact on Sensitive Electronics EV systems contain components that are not present in traditional vehicles, including:
Inaccurate or Misleading Results Using the wrong test voltage can also affect the accuracy of your readings. Too much voltage may:
Standards Behind Proper Isolation Testing Isolation testing procedures are not based on guesswork. They are supported by well-established industry standards and regulations. These include:
For technicians, this reinforces an important principle: Testing should follow engineered guidelines—not assumptions. Precision Over Power: The Correct Approach Isolation testing in EV systems is not about pushing equipment to its limits. It is about applying the correct methodology for the system under test. A proper approach includes:
What This Means for Technicians and Shops As EV systems become more common in service bays, the margin for error in diagnostics becomes smaller. Technicians must move beyond generalized assumptions and develop a deeper understanding of:
The Bigger Picture: EV Diagnostics Is Different Isolation testing is just one example of a broader shift happening in the automotive industry. EV diagnostics require:
This is where training and understanding become critical. Final Takeaway Isolation testing is not about using the highest voltage available. It is about selecting the correct voltage based on system design and OEM requirements. Using excessive voltage does not improve accuracy—it introduces risk.The technicians who understand this distinction will be the ones performing safer, more reliable diagnostics as EV adoption continues to grow. Contact Us If you would like to discuss EV isolation testing procedures, diagnostic strategies, or technician training, contact us at: [email protected] We welcome technical discussion. References:
 Rethinking Maintenance in the Age of Electric Vehicles.
A common misconception in today’s automotive industry is that electric and hybrid vehicles do not require maintenance. As EV adoption continues to grow, this belief is becoming more widespread—often leading to confusion among both consumers and service professionals. At a surface level, the assumption makes sense. Electric vehicles eliminate many of the traditional service items associated with internal combustion engines. There are no oil changes, fewer moving parts, and less reliance on combustion-driven systems. However, this perspective only tells part of the story. Maintenance in EVs hasn’t disappeared—it has fundamentally shifted. Understanding that shift is critical for repair shops, technicians, and industry professionals who want to remain relevant and competitive as the vehicle landscape continues to evolve. Why the “Maintenance-Free EV” Narrative Persists The idea that EVs require little to no maintenance is largely driven by simplified messaging. Automakers and media outlets often emphasize reduced maintenance costs as a key benefit of electrification. While technically accurate in certain areas, this messaging can unintentionally create the impression that EVs are entirely maintenance-free. In reality, EVs replace many traditional service items with new systems that require a different type of attention. Instead of focusing primarily on mechanical wear, maintenance shifts toward electrical systems, thermal management, and advanced diagnostics. This distinction is important. While the frequency and type of service may change, the need for regular inspection, monitoring, and maintenance remains. What Maintenance Still Looks Like in EVs and Hybrids Even without an internal combustion engine, electric and hybrid vehicles rely on multiple systems that require ongoing service. In many cases, these systems are just as critical—if not more so—than their traditional counterparts. Tires and Suspension Systems: Electric vehicles are typically heavier than internal combustion vehicles due to the weight of their battery packs. This additional mass has a direct impact on tire wear and suspension performance. Increased vehicle weight, combined with instant torque delivery, often results in accelerated tire wear. Suspension components also experience greater stress, making routine inspections essential for maintaining ride quality and safety. For many shops, tire service remains one of the most consistent and immediate opportunities when servicing EVs. Brake Systems and Regenerative Braking: While regenerative braking systems reduce the frequency of traditional brake use, they do not eliminate the need for brake maintenance. In fact, reduced brake usage can introduce new challenges. Brake components may be more susceptible to corrosion due to lack of regular friction, and calipers can become seized if not properly maintained. This creates a shift from predictable wear-based replacement to condition-based inspection, requiring technicians to approach brake service differently than they would on ICE vehicles. Thermal Management Systems: One of the most critical—and often overlooked—areas of EV maintenance is thermal management. Electric vehicles rely on complex cooling systems to regulate the temperature of:
Neglecting thermal management maintenance can lead to reduced system performance, accelerated battery degradation, and in some cases, costly component failures. High-Voltage Battery Health and Monitoring: The high-voltage battery is the most valuable and essential component of any electric vehicle. While it does not require traditional “maintenance” in the same sense as mechanical components, it does require ongoing monitoring and evaluation. Technicians must be able to assess:
Power Electronics and Electrical Systems: EVs introduce a level of electrical complexity that goes far beyond traditional automotive systems. Components such as inverters, converters, and onboard chargers play a critical role in vehicle operation. These systems must be properly inspected, tested, and diagnosed when issues arise. Unlike mechanical failures, electrical issues often require a deeper understanding of system interaction and behavior. As a result, successful EV service is increasingly dependent on diagnostic skill and system-level thinking. 12-Volt Battery Systems: Despite being fully electric, EVs still rely on a conventional 12-volt battery to power auxiliary systems. These batteries are responsible for critical functions such as control systems, lighting, and vehicle startup processes. Failures in the 12V system can lead to significant vehicle issues, making regular testing and replacement an important part of EV maintenance. Software, Updates, and Calibration: Another key difference in EV maintenance is the role of software. Modern electric vehicles rely heavily on firmware, control modules, and system calibrations. Software updates can impact performance, efficiency, and even safety systems. Shops that are not equipped to handle software-related service may find themselves unable to fully support modern vehicles, even if they understand the hardware. The Real Shift: From Mechanical Service to System-Level Diagnostics The most significant change in EV maintenance is not the reduction of work—it is the transformation of the work itself. Traditional automotive service has been heavily focused on mechanical systems and component replacement. EV service, by contrast, requires a deeper understanding of:
What This Means for Repair Shops As EV adoption continues to grow, repair shops are facing a critical decision: adapt or fall behind. Shops that invest in EV education and training are beginning to position themselves as leaders in a rapidly changing market. They are building confidence in high-voltage safety, developing diagnostic capabilities, and expanding their service offerings. On the other hand, shops that delay or avoid EV service risk losing not only new opportunities, but also existing customers who transition to electric vehicles. This is not a distant future scenario—it is already happening in service bays today. The Opportunity Hidden in the Shift One of the most overlooked aspects of EV maintenance is the opportunity it presents. Customers who own EVs still require:
Shops that step into this space early are not just capturing new revenue—they are building long-term customer relationships in a segment that will continue to grow. Why Waiting Comes at a Cost Taking a “wait and see” approach to EV adoption may feel safe, but it carries long-term risk. As more vehicles on the road become electrified, the percentage of serviceable ICE vehicles will gradually decline. Shops that are not prepared to service EVs may find themselves with a shrinking customer base. More importantly, once a customer establishes a relationship with an EV-capable shop, they are unlikely to return to a shop that cannot service their vehicle. Preparing for the Future of Service Adapting to EV maintenance does not require an immediate, large-scale overhaul. However, it does require intentional action. The most effective starting points include:
How EVPro+ Supports the Transition EVPro+ is designed to help technicians, shop owners, and educators build real-world EV competency. Through structured training and hands-on experience, participants gain a clear understanding of:
Final Takeaway Electric and hybrid vehicles do not eliminate maintenance. They redefine it. The shops that recognize this shift and take action today will be the ones leading the industry tomorrow. Those that don’t risk being left behind as the automotive landscape continues to evolve. If you would like to discuss EV blended braking diagnostics or technician training strategies, contact us at: [email protected] We welcome technical discussion. References: U.S. Department of Energy – Alternative Fuels Data Center (AFDC), OEM EV maintenance schedules. Disclaimer: This content is provided for general informational purposes only. It is based on publicly available data, standards, and published sources available at the time of release. It does not constitute advice of any kind. Information is provided as-is, without warranties, and no liability is assumed for actions taken based on this content.  As electrified vehicles become more common in service bays, blended braking systems are still widely misunderstood.
One of the most frequent assumptions when a customer reports brake pedal pulsation is: “It must be regenerative braking.” Let’s break that down. MYTH If there is a pulsation during braking on an EV, it is caused by regenerative braking. FACT Regenerative braking does not create brake pedal pulsation. Pulsation is almost always caused by issues in the friction braking system, such as rotor thickness variation, heat spots, or uneven pad deposits. EVs use blended braking systems that combine regenerative and friction braking. When pulsation is felt, the root cause can be determined by isolating the base mechanical/hydraulic braking from regenerative braking by forcing the system to use only base (hydraulic/mechanical braking) and excluding electronic/electric braking. Why This Myth Persists Electrified vehicles feel different under braking. The transition between regenerative and friction braking can alter pedal feel, especially at low speeds. Because this behavior is unique to EVs and hybrids, technicians and customers may assume that any abnormal sensation must originate from the regenerative system. However, pedal pulsation is a mechanical symptom. It is not produced by electronic regenerative torque application. Understanding Blended Braking Systems EVs and hybrids use blended braking systems that combine:
Pulsation, on the other hand, is typically caused by mechanical inconsistencies in the friction system, including:
When pulsation is present, the correct diagnostic approach is to isolate the friction braking system from regenerative braking. By forcing the vehicle into a mode that relies solely on hydraulic/mechanical braking, the root cause can be accurately identified. The Diagnostic Importance Misdiagnosing brake pulsation as a regenerative issue can lead to:
Standards and guidance related to brake system performance include:
Key Takeaway Brake pulsation in EVs is a friction brake issue—not a regenerative braking fault. Understanding how blended braking systems function allows technicians to diagnose accurately and avoid unnecessary component replacement. If you would like to discuss EV blended braking diagnostics or technician training strategies, contact us at: [email protected] We welcome technical discussion. Technical References OEM EV brake service documentation SAE brake system guidance FMVSS 105 and 135 Disclaimer This content is provided for general informational purposes only. It is based on publicly available data, standards, and published sources available at the time of release. It does not constitute advice of any kind. Information is provided as-is, without warranties, and no liability is assumed for actions taken based on this content.  Category: Technical Diagnostics / Business Development
Two Electrical Tests Do not Define Electric Machine (i.e., Motor or Generator) Health Electric machines are at the core of electrified propulsion and vehicle performance. From traction Electric Machines to generators and electric A/C compressors, their reliability directly impacts vehicle systems operation and customer satisfaction. Yet, one misconception continues to surface in the industry: MYTH There are only two tests needed to determine the State of Health of an Electric Machine: insulation resistance and stator winding resistance. FACT The state of health of an electric machine (motors, generators, A/C compressors, etc.) cannot be determined by using only one or two electrical tests. A proper assessment requires evaluating the electrical condition of all Electric Machine components, including Stator windings, Rotor condition, contamination, ground faults, and electrical connections. Modern Electric Machine diagnostics use multi-parameter testing to identify developing faults that may not be visible using only basic resistance or insulation resistance testing. For example, Electric Machine Circuit Analysis (MCA) testing combines multiple static and dynamic measurements to assess Stator winding integrity, Rotor condition, insulation resistance and overall Electric Machine health. Techniques such as Test Value Static™ (TVS™) that uses 4 different electrical test metrics (Inductance, Impedance, Phase Angle, and Current-to-Hz Ratio), along with 4 other test metrics (Capacitance, Insulation Resistance, Dissipation Factor, and Phase Winding Resistance) to establish a baseline reference metrics for static testing, where changes over time indicate developing Stator or Rotor faults. Dynamic Stator and Rotor signature analysis can further evaluate the condition of both components in a single test, to further determine whether a pending/current failure is located in the Stator or Rotor system. Additionally, the TVS measurement can determine whether current or pending Electric Machine failures are electrical or magnetic (i.e., Stator Winding performance, Permanent Magnet Rotor or Induction Machine Rotor Bars). This testing results in an effective method for acceptance testing of new or repaired electric machines. Oscilloscopes and current clamps are an additional level of testing that can provide visual representations for failing or failed Stators, Rotors, and bearings. Relying on limited testing metrics can overlook early or mid-stage electrical or magnetic degradation, similar to using minimal diagnostic tools and processes to determine the root cause for a poor performing ICE system. Why This Myth Persists For decades, traditional Electric Machine testing often focused on:
They cannot identify hidden pending or catastrophic failures. They are far less effective at detecting early-stage degradation. As electrified vehicle systems become more complex, simplified testing approaches create blind spots. What Proper SOH Assessment Requires Accurate electric machine State of Health (SOH) evaluation requires analysis of:
This is critical for:
The Business Impact of Incomplete Testing This is not just a technical conversation. Incomplete testing can lead to:
Key Takeaway Accurate electric machine SOH assessment requires comprehensive electrical testing, not shortcuts. Using multi-test diagnostic methods allows technicians to identify faults early, validate repairs, and make informed service decisions—improving reliability while creating legitimate service value. Continue the Conversation If you would like to discuss implementing advanced electric machine diagnostics in your shop, contact us at: [email protected] We welcome technical dialogue. Technical References IEEE 43 IEEE 1415 IEC 60034-27-4 Disclaimer This content is provided for general informational purposes only. It is based on publicly available data, standards, and published sources available at the time of release. It does not constitute advice of any kind. Information is provided as-is, without warranties, and no liability is assumed for actions taken based on this content.  Electrification isn’t just changing vehicles — it’s reshaping the skill set required to service them. As EV systems become more advanced, technicians must adapt to high-voltage safety procedures, battery diagnostics, power electronics, and evolving software-driven architectures.
This MOTOR article explores how EV technology is transforming the technician role and why ongoing education is no longer optional. Shops that prioritize training and workforce development are better positioned to stay competitive, reduce liability, and confidently service the next generation of vehicles. At EVPro+, we believe technician advancement is the foundation of industry advancement. → Read the full article on MOTOR Originally published on MOTOR. Shared by EVPro+ to support industry-wide education and workforce readiness. |
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