Drive Motor "B" Inverter Performance
The P0A79 code means the vehicle's onboard diagnostic system has detected: Drive Motor "B" Inverter Performance. This is a serious severity code.
- Keep driving?
- Short distances only
- DIY difficulty
- hard
- Estimated cost
- $300 - $4,000 (cooling or wiring causes at the low end; inverter power-stage service at the high end - diagnose first)
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Common Symptoms
- Check Engine Light and hybrid system warning on
- Reduced power or the affected motor disabled
- Vehicle may enter limp mode
- Possible whining or reduced smoothness from the electric drive
Probable Causes (Ranked by Likelihood)
- Fault inside the Drive Motor "B" Inverter power stage (IGBTs) High
- Inverter cooling problem - low coolant, failed pump - degrading performance before hard failure High
- Phase wiring or motor winding fault loading the inverter Moderate
- HV supply voltage out of range during operation Moderate
Frequently Asked Questions
What does P0A79 mean?
P0A79 means the Drive Motor "B" Inverter is not delivering the commanded output. The inverter converts DC battery power to the three-phase AC that drives the motor.
Can I keep driving with P0A79?
Short distances only. Inverter faults can escalate to a shutdown, and driving through one can take the motor down with it.
Is P0A79 safe to work on myself?
This code involves the high-voltage system. Do not open the HV battery, inverter, or any orange-cabled component without hybrid-specific training, insulated gloves, and the service plug removed. Diagnosis beyond a scan-tool read belongs at a hybrid-qualified shop.
Mechanics Guide Step-by-step diagnosis
Step-by-Step Diagnostic Procedure
-
Read all inverter, motor, and battery codes together - performance codes usually travel with companions that localize the fault.
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Check the inverter cooling loop first: coolant level and pump operation. Heat is the most repairable cause.
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Review freeze-frame temperature and voltage at the moment the code set.
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With the HV system verified de-energized, test motor windings and phase cables so a motor fault is not blamed on the inverter.
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Follow the OEM matrix for inverter internal diagnosis before replacement.
Sources 1
This page is built from documented references. Verify against your own service info before repair work.
- SAE J2012Diagnostic Trouble Code Definitions (defines the generic OBD-II code ranges)
Commonly Affected Vehicles
- Toyota/Lexus hybrids (Prius, Camry Hybrid, RAV4 Hybrid)
- Ford/Lincoln hybrids (Escape, Fusion, C-MAX)
- Honda hybrids (Insight, Civic Hybrid, Accord Hybrid)
- Hyundai/Kia hybrids and plug-in hybrids
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