P0A91Drive Motor B Performance
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- How the car detects it
- P0A91 is set when the second electric drive motor (motor B) of a hybrid or electric vehicle does not deliver the expected speed or torque, although no electrical circuit fault is detected. Motor B exists only on systems with two traction motors, such as power-split or dual-motor layouts. CARB requires hybrid OBD systems to monitor electric motor performance. No manufacturer documents this code publicly; GM's tables describe the motor A equivalent P0A90 as a comparison between motor speed and a reference speed, which illustrates the approach. Causes range from inverter or resolver faults to mechanical damage. The vehicle usually limits power or enters a reduced mode. P0A79 covers inverter B performance.
- What you may notice
- Hybrid/EV system warning and MIL
- Reduced power or limp mode
- Likely causes
- PossibleInverter B fault limiting motor current
- PossibleMotor position sensor (resolver) signal error
- RareMechanical damage to motor B or its gearing
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Workshop only · Usually a job for a workshop.Typical cost: €200 – €5,000
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.