Diagnosing PHEV Charging and EV Mode Faults

Plug-in hybrid charging complaints are increasingly common as more PHEVs hit the road. The customer says it will not charge, it charges slowly, or it will not drive in EV mode. These are three different problems with different diagnostic paths.

Start with the basics: verify the charge port indicator lights are working, the charge cable is not damaged, and the outlet has power. Plug a known-good device into the outlet to verify power. Check the charge port for debris, corrosion, or a stuck latch. Many PHEVs have a charge port latch that must be in the correct position before charging begins — if the latch solenoid is stuck, charging will not initiate. Check DTCs in the onboard charger module and the HV battery management system. Common faults: onboard charger failure (no output despite AC input), ground fault detection (the charger detects a ground leak in the HV system and refuses to charge for safety), pilot signal fault (the communication between the charge station and the vehicle fails), or a blown fuse in the charge circuit.

Verify the charge level being used. Level 1 (120V) charging is inherently slow — a PHEV with a 15 kWh battery on Level 1 takes 8 to 12 hours. Level 2 (240V) cuts that to 2 to 4 hours. If the customer thinks it is slow, they may just be on Level 1. If it truly is slower than expected on Level 2, check the onboard charger output current — it should match the charger's rated capacity. Some vehicles reduce charge rate when the battery is too hot or too cold (the BMS protects the battery by limiting charge current). Check battery temperature in scan data. Also check for a reduced EVSE (Electric Vehicle Supply Equipment) rating — some Level 2 stations or home chargers limit output to 16A instead of the full 32A.

If the vehicle will not drive in EV mode, check the battery state of charge — most PHEVs require at least 15 to 25 percent charge to allow EV mode. Check battery temperature — the BMS may disable EV mode if the battery is too cold (below about 0°C) or too hot. Check for DTCs in the motor controller, battery management system, and hybrid control module. A failed motor position sensor, inverter fault, or battery contactor fault can all prevent EV mode. On some vehicles, the engine must be warm enough before EV mode is allowed — if the engine coolant temperature is very low, the vehicle may run the engine to heat the cabin and catalyst regardless of battery charge.