What it means
The control module detects that drive motor B performance is outside its expected range.
At a glance
- Usually lights the check-engine light
- The engine or gearbox may go into limp mode
How it works
Drive motor B is a traction motor in the hybrid or electric drive system, and its inverter channel controls the high-voltage power it uses. The control module sets P0A91 when motor B's observed performance does not match the expected range; this specifically points to motor B's performance path and does not alone establish that the motor itself is defective.
Common causes
Most likely first.
- Drive motor fault
- Motor wiring or high-voltage connection fault
- Motor control or inverter fault
Symptoms
- EV/hybrid system warning light on
- Reduced motor power or torque
- Possible limp mode or vehicle shutdown
How to diagnose it
- Record freeze-frame data and examine hybrid live data for motor B, comparing requested and actual torque or speed where supported.
- Check for companion codes involving motor B, its inverter channel, high-voltage supply, or feedback sensors before focusing on the motor.
- After following the manufacturer's high-voltage shutdown procedure, inspect accessible motor B wiring and connectors for damage, corrosion, loose fit, or overheating.
- Test motor B feedback circuits and control wiring for continuity and signal quality using the manufacturer's procedure.
- If external circuits pass, use vehicle-specific hybrid diagnostics to distinguish an internal motor B fault from an inverter fault.
Common fixes
- Repair a damaged or poorly connected motor B harness or connector.
- Repair the motor B feedback or control circuit if testing identifies a wiring fault.
- Repair or replace the inverter channel serving motor B if diagnostics isolate it.
- Repair or replace drive motor B if tests confirm an internal performance fault.
Can I keep driving?
Limit driving and avoid high-load acceleration because reduced motor B output can cause weak or uneven propulsion, limp mode, or shutdown. Stop safely if power becomes unpredictable; high-voltage system checks require appropriate training.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.