P0A79: Drive Motor B Inverter Performance

What it means

The control module detects that drive motor B inverter performance is outside its expected range. The code does not identify a specific internal failure.

At a glance

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

How it works

The inverter for drive motor B converts power between the high-voltage battery and motor B. The control module sets P0A79 when monitored drive motor B inverter performance is outside its expected range, without pinpointing an internal failure.

Common causes

Most likely first.

1. Inverter or power electronics fault
2. Inverter cooling problem
3. High-voltage connection or wiring fault

Symptoms

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

How to diagnose it

1. Save freeze-frame data and scan all hybrid system modules for related inverter, motor, temperature, and voltage codes to identify when the drive motor B fault occurred.
2. With the vehicle safely powered down according to its manufacturer’s instructions, inspect drive motor B inverter connectors and high-voltage wiring for damage, corrosion, looseness, or overheating.
3. Check the inverter cooling path for blocked airflow, coolant loss, leaks, or a fan that fails to respond to a command.
4. Compare drive motor B inverter live data, including temperatures and commanded versus reported operation, with drive motor A data where available.
5. Have a qualified hybrid technician test the drive motor B inverter and its high-voltage connections using the manufacturer’s procedures and specifications.

Common fixes

• Clear debris or restore airflow through the drive motor B inverter cooling path.
• Repair damaged inverter control wiring or a loose or corroded connector.
• Repair a leak or other fault in the inverter cooling system.
• Repair or replace the drive motor B inverter if testing confirms an internal power-electronics fault.

Can I keep driving?

Keep trips short and avoid hard acceleration because motor B may provide reduced torque or the vehicle may enter limp mode. Stop safely and arrange assistance if power falls sharply or a shutdown warning appears.