Faulty inverter assembly internal to the drive motor B circuit, such as failed insulated-gate bipolar transistors (IGBTs) or capacitors; Damaged or corroded high-voltage wiring and connectors between the inverter and motor B; Coolant leaks or blockages causing inverter overheating and performance degradation; Software calibration issues in the hybrid control module requiring reprogramming; Failed current or voltage sensors within the inverter that misreport output; Ground fault or short circuit in the motor B windings affecting inverter load; Low or contaminated inverter coolant reducing heat dissipation

DTC codes / P0Axx · Hybrid propulsion / P0A79

P0A79Drive Motor B Inverter Performance

Q: What does code P0A79 mean?

Drive Motor B Inverter Performance. P0A79 indicates that the inverter responsible for converting direct current (DC) to alternating current (AC) for drive motor B has reported a performance fault to the hybrid or electric vehicle control module. The computer monitors the inverter's output and internal switching, and it sets this code when the actual electrical output does not match the commanded values within a calibrated time window.

P0A79 indicates that the inverter responsible for converting direct current (DC) to alternating current (AC) for drive motor B has reported a performance fault to the hybrid or electric vehicle control module. The computer monitors the inverter's output and internal switching, and it sets this code when the actual electrical output does not match the commanded values within a calibrated time window.

SystemPowertrain

Code typeGeneric (all makes)

SeverityHigh

Fix difficultyProfessional

AreaHybrid propulsion

Symptoms you may notice

Illumination of the hybrid system warning light or check engine light, often with no other noticeable symptoms
Reduced power output or a limp-home mode that limits vehicle speed
The vehicle may refuse to start or enter 'Ready' mode
Audible whining or buzzing from the inverter area during acceleration
Intermittent stalling or sudden loss of propulsion while driving
Overheating warning for the inverter or motor, leading to power derating

Common causes, most likely first

Faulty inverter assembly internal to the drive motor B circuit, such as failed insulated-gate bipolar transistors (IGBTs) or capacitors
Damaged or corroded high-voltage wiring and connectors between the inverter and motor B
Coolant leaks or blockages causing inverter overheating and performance degradation
Software calibration issues in the hybrid control module requiring reprogramming
Failed current or voltage sensors within the inverter that misreport output
Ground fault or short circuit in the motor B windings affecting inverter load
Low or contaminated inverter coolant reducing heat dissipation

How to diagnose and fix it

Perform a thorough visual inspection of high-voltage cables, connectors, and inverter coolant lines for damage or leaks
Use a scan tool to retrieve all hybrid system codes and freeze-frame data to confirm the fault conditions
Check inverter coolant level and condition, and verify coolant pump operation
Measure high-voltage insulation resistance and check for ground faults in the motor B circuit
Reprogram the hybrid control module with the latest manufacturer software updates
Replace the inverter assembly if internal component failure is confirmed
Clear codes and perform a road test to verify the repair and ensure no pending codes return

Inverter Performance Codes Often Misdiagnosed

A weak or failing 12-volt auxiliary battery can cause erratic hybrid control module behavior and set false inverter performance codes, so always load-test the battery first.
Inverter coolant that has never been serviced can degrade and clog the cooling passages, leading to overheating and performance faults without any visible leak.
The code may be stored due to a communication error between the inverter and the hybrid control module rather than an actual inverter failure, so check controller area network (CAN) bus integrity.
After replacing an inverter, some vehicles require a calibration or 'learn' procedure for the new unit to communicate properly, and skipping this step can cause the code to reset immediately.
A failing motor B resolver or position sensor can cause the inverter to command incorrect output, mimicking an inverter fault; always inspect motor sensors before condemning the inverter.

Can I keep driving with P0A79?

Do not continue driving with this code set, as the vehicle may enter a reduced-power mode or shut down unexpectedly, increasing the risk of a crash. Have the vehicle towed to a qualified hybrid service center for diagnosis.

Tools that help

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