Powertrain, generic · Hybrid propulsion

P0A91 Drive Motor B Performance

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

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.

Likely causes

Inverter B fault limiting motor current
Motor position sensor (resolver) signal error
Mechanical damage to motor B or its gearing

Symptoms

  • Hybrid/EV system warning and MIL
  • Reduced power or limp mode

Repair estimate

DifficultyShop_onlyWorkshop job
Parts and labour€200–5,000
Time1–8 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

drive motor b

Related codes

P0A90P0A92P0A79

References: law.cornell.edu, gsi.ext.gm.com.