HEV Diagnosis and Repair: Safety, Workflows, and New RAM ProMaster BPCM Coverage

This article is not a step‑by‑step repair guide or a substitute for certified high‑voltage training. Working on HEV vehicles requires formal HEV training, OEM‑approved procedures, and the correct PPE and tooling. Improper handling of high‑voltage systems can result in serious injury or death. Always follow OEM service information and local regulations. Snap‑on assumes no responsibility for injury, damage, or improper application of this information. 

 

EV Systems: How They Are Engineered & How They Work 

Battery 

• Multiple small, low-voltage batteries linked in series 

• Results in high DC voltage (300-400V+) 

• Nickel Metal Hydride or Lithium-ion 

• EVs have large packs – Quite heavy 

Many EV systems are structural and part of the frame, so EVs often require specific lifts and battery lifting equipment. If the vehicle is purely EV, the electric motor and battery are placed first and the rest of the vehicle is built around them. If the platform also has gasoline/diesel variants, the EV system is designed to fit within an existing ICE layout — many components will resemble traditional ICE components. Battery size varies depending on the platform and construction. 

 

EV Components Include: 

• Battery 

• Battery cooling/heating system 

• Voltage converter 

• Regenerative braking system 

• Electric motor 

• Charger 

 

There are no federal certifications required to work on EVs in the United States. 
Although legal, this is not recommended without proper high-voltage training. 

 

Battery 

• Multiple small, low-voltage batteries linked in series 

• Results in high DC voltage (300-400V+) 

• Nickel Metal Hydride or Lithium-ion 

• EVs have large packs – quite heavy 

 

Battery Thermal Management 

Inverter and DCDC Converter 

• Converts battery DC into 3phase AC for the motor 

• During regenerative braking, converts AC back to DC to charge the battery 

• DCDC converter provides 12volt power for vehicle systems 

• Operates with high current and voltage — diagnostics are done via scan tool, not direct probing 

• Often liquid cooled and part of the HV safety loop 

 

Monitoring & Control 

 

Battery control modules monitor: 

• Block voltages 

• Temperatures 

• Current 

• SOC (state of charge) 

• Isolation resistance 

• Contactor / precharge status 

 

Tech Tip: Check min/max block voltage and block delta. Large deltas often set P0BBD00 (battery pack voltage variation exceeded limit). 

 

Battery Block 

Battery control module sense wires: 
a) Block 1 
b) Block 2 
c) Block 3 

With your scan tool, you can view individual battery block voltages. 

 

High Voltage Safety — Essential Practices Before Any Diagnostic Work 

Important Notice: This section is for awareness and general guidance only — it is not instructional. Working on high‑voltage systems requires formal HEV training, OEM repair information, and approved safety equipment. Snap‑on does not assume responsibility for injury, damage, or incorrect application of the information presented. 

Always follow OEM procedures and local regulations before performing any work on high‑voltage systems. 

 

Minimum Practice Checklist 

1. Deenergize and wait: follow OEM shutdown and discharge periods.energize &  

2. PPE: tested class 0 gloves, arc‑rated clothing, face shield, and HV‑safe footwear. 

3. Lockout/Tagout: secure disconnects and post signage. 

4. Tools and meters: insulated tools; CAT III/IV ≥1,000 V multimeter. 
   Never pierce HV cables. 

5. Training: HEV training is strongly advised. 

 

Electric Motor, Resolver & Reduction Gear 

Electric Motor 

Resolver 

• Internal position sensor 

• Determines rotor speed and position 

• Incorrect data → reduced power, no‑start, or harsh engagement 

• After certain repairs, a resolver reinitialization is required 

Charging & Regenerative Braking 

Charging circuit diagram through ShopKey Pro Repair Information – 2019 Hyundai Kona Electric

 

 

Regenerative Braking 

• Motor becomes a generator 

• Converts motion back into electrical energy 

• Reduces hydraulic brake wear 

• Hydraulic brakes still required at low speeds, high speeds, or when battery is full 

 

Golden Rules: 

1. Scan tool first — HEVs depend on coordinated communication between modules (BPCM, inverter, charger, ABS, HVAC, etc.), so issues are usually identified through scan‑tool data rather than direct circuit testing. 

2. 12 V battery health is critical. 

3. Avoid using a lab scope on HV circuits unless you have rated probes and OEM procedures. 

4. Visual inspection is essential: seals, connectors, coolant, heat damage. 

Hybrid Systems Overview 

Hybrid Battery

Squashing a myth: 

A common belief is that you can’t diagnose or repair much on an HEV because a scope can’t be used on high‑voltage circuits. That part is true — you should never scope HV circuits without the correct rated equipment and OEM approval. 

But that doesn’t mean you can’t work on HEVs, or that you should avoid them. 

Modern HEVs are built around software, control modules, and networked electronics, just like ICE vehicles. 
This means most real‑world diagnosis happens through your scan tool, not on the high‑voltage circuits themselves. 

Many HEV faults are: 

• Logic‑driven 

• Module‑managed 

• Resolved through scan‑tool resets, calibrations, and functional tests 

 

Beyond the high‑voltage system, HEVs still rely on all the everyday vehicle systems you diagnose regularly, including: 

 

• Body control functions (doors, windows, lighting, immobilizer, keyless entry) 

• ADAS systems (radar, camera, ultrasonic, lane/park‑assist calibrations) 

• HVAC (electric compressors, blend doors, sensors) 

• Chassis systems (ABS, stability control, air suspension on some models) 

• Steering and braking modules 

• Instrument panel and infotainment 

• 12‑volt battery and power‑management systems 

• Network communications (CAN, LIN, FlexRay) 

 

All of these require a scan tool — exactly as they do on gasoline and diesel vehicles. 

Your Snap‑on diagnostic platform gives you access to: 

• Diagnostic trouble codes (DTCs) 

• Module data 

• Resets 

• Calibrations 

• Functional tests 

• Network checks 

• Service intervals 

• TPMS, HVAC, body‑system functions, thermal‑management data, and more 

 

You can diagnose far more on an HEV than many technicians think — and avoiding them only means falling behind. 
 

HEVs are already in your bay. Stay prepared, stay trained, and keep your platform updated to stay in the game. 

Exclusive New Functionality in your Snap‑on Diagnostic Tool

RAM ProMaster 2024–2025 — Battery Pack Control Module (BPCM)  

New Supported Procedures: 

Enable HV (High Voltage) Battery Contactors 

• This procedure will enable (close) the high-voltage battery contactors and is required after the HV battery pack is replaced. 

 

HVB Cell Voltage Difference Fault Reset 

Resets the HVB (high-voltage battery) cell voltage difference fault in the BPCM and is required to clear: 

• P0BBD00 — Hybrid battery pack voltage variation exceeded limit 

 

HVB Impact Event Reset 

Required to clear: 

• P167B00 — Control System Shutdown 

 

HVB Isolation Fault Reset 

Resets isolation-related faults in the BPCM and is required to clear: 

• P0AA6-00 — Hybrid battery voltage system isolation fault00 — Hybrid battery voltage system isolation fault 

• P0AA8-00 — Hybrid battery voltage isolation sensor circuit range/performance00 — Hybrid battery voltage isolation sensor circuit range/performance 

 

Tip: At the end of this procedure, BPCM DTCs are automatically cleared and reread. 
If P0AA6-00 or P0AA8-00 are still active, refer to service information for diagnostic steps.read.00 or P0AA8AA are still active, refer to service information for diagnostic steps. 

 

Important: Repair the following active DTCs before performing this reset: 

• P0AA7-00 — Hybrid/EV battery voltage isolation sensor circuit00 — Hybrid/EV battery voltage isolation sensor circuit 

• P1E1B-00 — Hybrid/EV battery side voltage system isolation00 — Hybrid/EV battery side voltage system isolation 

 

Isolation Test 

Initiates the isolation test for the entire vehicle’s HV system: 

• Battery pack + vehicle side (if contactors can close) 

• Battery pack only side (if contactors cannot close) 

 

After the test completes, the tool will display the measured isolation impedance. 

 

Stuck Contactor Fault Resets 

Complete these if any of the following DTCs are present: 

• P0AAA1-00 — Hybrid/EV Battery Positive Contactor “A” Stuck Closed00 — Hybrid/EV Battery Positive Contactor “A” Stuck Closed 

• P0AAA4-00 — Hybrid/EV Battery Negative Contactor “A” Stuck Closed00 — Hybrid/EV Battery Negative Contactor “A” Stuck Closed 

• P0D08-00 — Hybrid/EV Battery Positive Contactor “A” Stuck Closed00 — Hybrid/EV Battery Positive Contactor “A” Stuck Closed 

• P0D0F-00 — Hybrid/EV Battery Negative Contactor “A” Stuck Closed00 — Hybrid/EV Battery Negative Contactor “A” Stuck Closed 

 

Note: To ensure the reset is successful, the BPCM DTCs will be automatically cleared and reread at the end of this procedure. If any of the stuck contactor fault DTCs remain, refer to service and repair information for further diagnostics. 

7. OEM-Specific - TeslaSpecific — Tesla 

Model S and X (up to 2020): Standard OBDII Port 

These vehicles include a standard OBDII port, allowing a Snap-on diagnostic tool to connect directly and access a wide array of functions similar to a conventional ICE vehicle. 

Accessible Systems 

• Drive inverter/ “engine management” equivalents 

• ADAS 

• Instrument panel 

• SRS 

• Vehicle Alerts 

• Charging system 

• HVAC 

• BMS 

• BCM 

 

Battery‑related Tests 

• Clear counters 

• Reset alert codes (common Tesla alerts: W152, W153, W163, U019) 

• Refill/drain coolant 

• Coolant air purge 

 

Other Supported Tests 

• Air suspension: set ride height, read pressures 

• Occupant detection reset 

• TPMS relearn (Bluetooth) 

 

Key takeaway: 
Model S/X up to 2020 are like regular OBD-equipped vehicles for diagnostics which is a huge advantage for independent shops and a significant opportunity with the added capability of your scan tool brings to service and repair these vehicles.  

Model 3 / Model Y and Newer S/X 

• Many tests available through in-vehicle Service Mode or Service Mode Plus (subscription) 

• Full OEM info available via ShopKey Repair Information, (requires a ShopKey subscription, speak to your Snap-on Representative for more information) additionally, repair information is available directly from OEM via service.tesla.com 

Your Scan Tool Is the Key to HEV Success

HEV systems may seem unfamiliar, but much of the diagnostic work is software‑based and fully accessible through your scan tool. With proper safety practices, OEM procedures, and updated coverage, including RAM ProMaster BPCM functionality, technicians can diagnose and repair far more than expected. 

HEVs are already rolling past your shop. Stay prepared, keep your scan tool updated, and stay in the game. 

 

FAQ’s 

 

1. Can you diagnose an electric vehicle without working on the high-voltage system? 

Yes. Many HEV faults are software‑driven and module‑managed, meaning diagnosis is carried out using a scan tool, not by probing high‑voltage circuits. HEVs still contain all the familiar vehicle systems you diagnose daily — body controls, ADAS, HVAC, ABS/ESC, infotainment, TPMS, and more, all fully accessible through your scan tool. 

 

2. Do I need special certification to work on HEVs in the United States? 

No federal certification is legally required to work on HEVs in the U.S. However, formal high‑voltage safety training is strongly recommended before working on or near HV components. Always follow OEM safety procedures, service information, and local regulations. 

 

3. Can a scan tool reset or repair high-voltage battery faults? 

Yes. Many HEV battery‑related issues can be resolved using guided scan‑tool functions, such as: 

 

• High‑voltage contactor activation 

• Isolation fault resets 

• Impact‑event resets 

• Cell‑voltage variation resets 

• Guided isolation testing 

 

These functions are essential after repairs to HEV battery systems, such as those supported on the RAM ProMaster (2024–2025) BPCM. 

 

4. What HEV components require a scan tool to diagnose or reset? 

A scan tool is required for diagnosing: 

 

• Battery Management System (BMS) 

• Inverter/charger systems 

• ADAS modules 

• ABS/ESC 

• Electric HVAC components 

• Steering and braking modules 

• TPMS 

• Air suspension 

• Network communication faults (CAN/LIN/FlexRay) 

 

Because HEVs rely heavily on software‑orchestrated systems, accurate diagnosis depends on scan‑tool data, resets, and functional tests. 

 

5. Can HEVs be diagnosed in the same way as ICE vehicles? 

Yes — with differences. While HEVs add high‑voltage and electric‑drive components, they still use many of the same systems as ICE vehicles. The majority of faults in HEVs are identified through module communication, live data, and scan‑tool‑guided routines. High‑voltage areas, however, require specialised training and OEM procedures. 

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