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DTC codes / P0Exx · Hybrid propulsion / P0E91

P0E91Drive Motor A Inverter Voltage Sensor B Circuit Low

P0E91 indicates that the inverter for drive motor A has detected a low voltage condition on its 'B' voltage sensor circuit, which monitors a specific phase or internal bus voltage. The computer sets this code when the sensor signal falls below the expected threshold for a calibrated time, often indicating a short to ground, a faulty sensor, or a wiring issue.

SystemPowertrain
Code typeGeneric (all makes)
SeverityHigh
Fix difficultyProfessional
AreaHybrid propulsion

Symptoms you may notice

  • Illumination of the check engine light or service vehicle soon message
  • Reduced power or limp mode, as the inverter may limit motor output to protect components
  • Possible stalling or failure to start if the hybrid system disables the motor
  • Intermittent hesitation or rough operation under load
  • Often no symptoms besides the warning light, especially if the fault is intermittent

Common causes, most likely first

  1. Faulty voltage sensor B inside the inverter assembly
  2. Damaged or chafed wiring harness between the sensor and the inverter control module
  3. Corroded or loose electrical connector at the sensor or inverter
  4. Short to ground in the sensor signal circuit
  5. Internal inverter fault causing incorrect sensor readings
  6. Low auxiliary battery voltage or poor grounds affecting sensor reference voltage

How to diagnose and fix it

  1. Perform a visual inspection of the inverter wiring and connectors for damage or corrosion
  2. Check for technical service bulletins (TSBs) related to the inverter voltage sensor circuit
  3. Measure sensor reference voltage and signal voltage with a multimeter to verify the low condition
  4. Perform a voltage drop test on the sensor ground circuit to rule out high resistance
  5. Inspect and test the wiring harness for shorts to ground or open circuits
  6. If the sensor is integral to the inverter, follow manufacturer procedures to replace or repair the inverter assembly
  7. Clear codes and perform a road test to confirm the repair

Don't overlook the inverter ground

  • A poor ground connection at the inverter chassis can cause a low voltage sensor reading even when the sensor itself is good, so always check ground straps and mounting points.
  • Intermittent low voltage codes often stem from wiring chafing near hot or moving components, which may not be visible without wiggling the harness while monitoring live data.
  • The code can be set by a weak 12-volt auxiliary battery if the inverter's reference voltage drops during cranking, so load-test the battery before condemning the inverter.
  • Some manufacturers require a software update to the inverter control module to correct false low-voltage readings, so check for calibration updates before parts replacement.
  • This code does not always mean the inverter has failed; a simple connector pin tension issue can cause the same symptom and is far cheaper to fix.

Can I keep driving with P0E91?

If the vehicle enters limp mode or the warning light is accompanied by reduced power, avoid driving at high speeds or under heavy load and seek service promptly. Continued driving with a low voltage sensor fault may lead to inverter damage or a sudden loss of propulsion.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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