What Does P0A79 Mean?
DTC P0A79 indicates a general performance fault in drive motor "B" inverter (the secondary traction motor inverter, typically the rear motor in AWD hybrids or EVs). The control module detects that the inverter's actual output deviates from commanded values beyond acceptable tolerances. This may manifest as torque delivery errors, switching irregularities, or thermal protection activation on the secondary drive axis.
Safety Warning
Motor B inverter failure disables the secondary drive motor, eliminating AWD capability and reducing total available torque. In rear-motor-primary configurations, this could result in a complete loss of propulsion. Degraded IGBT operation risks high-voltage arcing and thermal damage.
Common Causes
30%
IGBT power transistor degradation in the motor B inverter
20%
Motor B inverter cooling system blockage or pump failure
20%
DC bus capacitor degradation in the rear inverter assembly
15%
Gate driver circuit fault causing improper switching in motor B inverter
15%
High-voltage connection resistance at the rear inverter causing voltage drop
Diagnostic Steps
1
Step 1: Retrieve freeze frame data including motor B inverter temperature, DC bus voltage, motor B speed and torque, and battery SOC at fault time.
2
Step 2: Check for related DTCs: motor B current sensor faults (P0A55-P0A56), coolant codes, and high-voltage connection codes.
3
Step 3: Verify the rear inverter cooling loop is operational; check for coolant leaks, air pockets, or restricted flow to the rear unit.
4
Step 4: Inspect all high-voltage connections at the rear inverter for proper torque, corrosion, or heat damage indicating high-resistance joints.
5
Step 5: Run manufacturer-specific inverter diagnostics to test IGBT integrity and gate driver functionality on the motor B inverter.
6
Step 6: Replace the motor B inverter assembly if internal faults are confirmed; follow high-voltage safety lockout/tagout procedures.
Estimated Repair Cost
$1,000 - $5,000
Parts + labor, varies by vehicle and location
DTC P0A79 indicates a general performance fault in drive motor "B" inverter (the secondary traction motor inverter, typically the rear motor in AWD hybrids or EVs). The control module detects that the inverter's actual output deviates from commanded values beyond acceptable tolerances. This may mani...
The most common cause of P0A79 (Drive Motor "B" Inverter Performance) is: IGBT power transistor degradation in the motor B inverter
Typical repair costs for P0A79 range from $1,000 to $5,000, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Motor B inverter failure disables the secondary drive motor, eliminating AWD capability and reducing total available torque. In rear-motor-primary configurations, this could result in a complete loss of propulsion. Degraded IGBT operation risks high-voltage arcing and thermal damage.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0A79 to identify the root cause.
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Quick Info
Category
Powertrain
System
Hybrid/EV Powertrain - Drive Motor B Inverter
Difficulty
Type
Generic (SAE)
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