P0C79: Drive Motor A Inverter Voltage Too High

What it means

The drive motor A inverter voltage is above the expected limit. The cause depends on the vehicle.

At a glance

• Usually lights the check-engine light
• The engine or gearbox may go into limp mode

How it works

The drive motor A inverter switches high-voltage battery power to control motor A, and its DC link must stay within a controlled voltage range. The control module sets P0C79 when the voltage associated with motor A’s inverter rises above its calibrated limit, potentially during regenerative braking or because battery-management regulation is outside its expected range.

Common causes

Most likely first.

1. Regenerative braking overshoot
2. BMS regulation outside calibration

Symptoms

• EV/hybrid system warning light on
• Reduced motor power or torque
• Possible limp mode or vehicle shutdown

How to diagnose it

1. Read freeze-frame data and hybrid-system codes to determine whether the overvoltage occurred during regeneration, acceleration, or another operating condition.
2. Check live data for motor A inverter voltage and compare it with the manufacturer’s specification, noting whether the reading is sustained or brief.
3. Review battery-management and regenerative-braking data for related voltage-control or regeneration faults.
4. Inspect accessible motor A inverter connectors and wiring for damage or poor connections, following the vehicle’s high-voltage safety procedure.
5. If the data confirms an inverter voltage fault, have the motor A inverter and its control system tested to the manufacturer’s procedure.

Common fixes

• Repair damaged or loose wiring or connections serving the motor A inverter.
• Correct a confirmed regenerative-braking control fault affecting motor A inverter voltage.
• Repair or replace a battery-management component confirmed to be regulating voltage incorrectly.
• Repair or replace the motor A inverter if testing identifies it as the source of the overvoltage.

Can I keep driving?

Limit driving and avoid hard acceleration or conditions that demand strong regenerative braking; power may be reduced or the vehicle may shut down. If the vehicle enters limp mode or displays a high-voltage warning, stop in a safe place and arrange service.