EVT Diagnostics & Repair Procedures 4 — Questions and Answers
Question 1: A technician is diagnosing intermittent HV system faults that only appear after extended driving. What is the BEST diagnostic approach?
- Replace the HV battery immediately
- Perform a thermal soak test and monitor data PIDs during and after heat buildup (Correct answer)
- Clear DTCs and return the vehicle to the customer
- Inspect only the 12V fuse box
Correct answer: Perform a thermal soak test and monitor data PIDs during and after heat buildup
Thermal soak testing exposes temperature-sensitive faults in connectors, sensors, or components that only appear when the system reaches operating temperature.
Question 2: What is the function of the pyrotechnic safety switch (PSS) found in some EV battery packs?
- It automatically recharges depleted cells using pyrotechnic energy
- It disconnects HV circuits in milliseconds during a severe crash event (Correct answer)
- It balances cell voltages during fast charging
- It regulates coolant flow through the battery thermal system
Correct answer: It disconnects HV circuits in milliseconds during a severe crash event
A pyrotechnic safety switch uses a small explosive charge to physically sever the HV circuit almost instantaneously during a crash, preventing electrocution or fire.
Question 3: After replacing a high-voltage battery module, what procedure must be completed to ensure proper BMS operation?
- Perform a combustion engine idle relearn procedure
- Execute a battery module configuration or initialization procedure via scan tool (Correct answer)
- Bleed the power steering system
- Recalibrate the front radar sensor
Correct answer: Execute a battery module configuration or initialization procedure via scan tool
The BMS must be reconfigured or initialized to recognize the new module's cell chemistry, capacity, and serial data to manage it correctly.
Question 4: When testing the insulation of an EV HV cable harness, what voltage should the insulation tester (megohmmeter) apply to avoid damaging the cable insulation?
- 12V DC
- A voltage level appropriate for the cable's rated voltage class, per manufacturer specification (Correct answer)
- Always 1000V DC regardless of cable rating
- AC line voltage (120V)
Correct answer: A voltage level appropriate for the cable's rated voltage class, per manufacturer specification
Test voltage must be selected based on the cable's rated voltage class; using too high a test voltage can damage the insulation being tested.
Question 5: An EV's thermal management system shows the battery coolant temperature rising rapidly during DC fast charging. The coolant pump is confirmed operational. What is the NEXT component to check?
- The cabin HVAC compressor clutch
- The battery chiller (heat exchanger) and refrigerant charge in the thermal circuit (Correct answer)
- The motor resolver signal quality
- The 12V battery charge rate
Correct answer: The battery chiller (heat exchanger) and refrigerant charge in the thermal circuit
If the pump is working but temperature still rises, the battery chiller or refrigerant circuit is likely not removing heat effectively from the coolant loop.
Question 6: A technician finds a HV connector pin with green corrosion and elevated resistance. What is the correct repair procedure?
- Apply dielectric grease over the corrosion and reinstall
- Clean pins with approved electrical contact cleaner, inspect seals, and replace connector if resistance remains elevated (Correct answer)
- Solder the connector pins to eliminate the resistance
- Apply silicone sealant over the connector body
Correct answer: Clean pins with approved electrical contact cleaner, inspect seals, and replace connector if resistance remains elevated
Corroded HV connector pins must be cleaned properly; if cleaning doesn't restore resistance to spec, the connector assembly should be replaced to prevent arcing or intermittent faults.
Question 7: What does a 'current sensor rationality fault' in a BMS DTC typically indicate?
- The battery is discharging faster than rated
- The measured current value is inconsistent with expected values based on other system parameters (Correct answer)
- A cell is shorted internally
- The motor is drawing maximum torque
Correct answer: The measured current value is inconsistent with expected values based on other system parameters
A rationality fault means the BMS cross-checked the current sensor reading against other data (like voltage drop and SOC change) and found the values don't agree, indicating a faulty sensor or wiring.
EVT Diagnostics & Repair Procedures 4
A technician is diagnosing intermittent HV system faults that only appear after extended driving.
What is the BEST diagnostic approach?