P0A79 — Drive Motor “B” Inverter Performance #

Note: The description of this diagnostic trouble code (DTC) may vary depending on the vehicle manufacturer (OEM).

• Toyota/Lexus: “Drive Motor ‘B’ Inverter Performance”
• Honda: “Motor Inverter B Performance Problem”
• Chevrolet: “Drive Motor 2 Inverter System Performance”

Summary of Code P0A79 #

The P0A79 code is a generic OBD-II trouble code that indicates a performance issue within the inverter associated with the “B” drive motor of a hybrid or electric vehicle. The inverter is a critical component that converts high-voltage DC power from the battery into AC power for the electric drive motors. When the Engine Control Module (ECM) or Hybrid Control Module detects that the performance of this inverter is outside of the expected range, it sets the P0A79 code. This can lead to a reduction in vehicle performance, restricted electric drive, or even a no-start condition. Prompt diagnosis and repair are important to ensure both safety and drivability.

Common Symptoms for Code P0A79 #

When the P0A79 code is present, the vehicle often exhibits noticeable symptoms that indicate a malfunction in the drive motor “B” inverter system. Recognizing these signs early can help prevent further damage to the hybrid or electric system. Typical symptoms include:

• Illuminated Check Engine Light or hybrid system warning light
• Reduced power or “limp mode” operation
• Limited or no electric drive capability
• Unusual noises from the inverter assembly (such as whining or buzzing)
• Possible no-start condition in severe cases

Probable Causes of Code P0A79 #

The causes of a P0A79 code are typically related to electrical or mechanical faults within the inverter system, its associated wiring, or the drive motor “B” itself. The most frequent causes, in order of likelihood, include:

1. Malfunctioning inverter assembly (internal failure, overheating, or contamination)
2. Faulty or degraded high-voltage wiring/connectors to the drive motor or inverter
3. Defective cooling system for the inverter (low coolant, pump failure, or blocked passages)
4. Internal fault in drive motor “B” (shorted windings or insulation breakdown)
5. Software or calibration issue in the Hybrid Control Module (rare, but possible)

Step-by-Step Diagnosis for Code P0A79 #

A systematic approach is essential for accurately diagnosing the root cause of the P0A79 code. Rushing or skipping steps can lead to unnecessary parts replacement and increased costs. Here’s a proven diagnostic path:

1. Verify the presence of code P0A79 using a professional scan tool capable of reading hybrid/EV module data.
2. Check for additional codes (especially inverter, HV battery, or drive motor-related codes) that could provide context.
3. Inspect the high-voltage inverter coolant level and cooling system operation (look for leaks, check pump operation).
4. Perform a visual inspection of the inverter assembly and wiring for signs of damage, corrosion, or loose connectors.
5. Check for Technical Service Bulletins (TSBs) related to inverter performance for your specific vehicle model and year.
6. Use OEM diagnostic procedures to perform inverter and drive motor resistance, insulation, and performance tests.
7. Test the high-voltage wiring harness for continuity, short-to-ground, and short-to-power using a megohmmeter as specified by the OEM.
8. If all mechanical and electrical checks pass, consider software updates or module reprogramming per OEM recommendations.

Possible Repairs for Code P0A79 #

Once the cause of the P0A79 code has been identified, targeted repairs can restore normal function. Always follow safety precautions when working with high-voltage hybrid/electric systems. Typical repairs include:

• Replacing the inverter assembly if internal failure or performance degradation is confirmed
• Repairing or replacing damaged high-voltage wiring or connectors
• Restoring the inverter cooling system by replacing the coolant, fixing leaks, or replacing a faulty coolant pump
• Replacing the drive motor “B” if internal faults are detected
• Reprogramming or updating the Hybrid Control Module as directed by the OEM

Is It Safe to Drive with Code P0A79? #

Driving with the P0A79 code is not recommended. While the vehicle may enter a reduced power (limp) mode to protect itself, continued operation can risk further damage to expensive hybrid/electric components. In some cases, the vehicle may stall or fail to restart, leaving you stranded. Always address this code promptly, and avoid driving until a professional assessment is completed.

Vehicles Most Commonly Affected by Code P0A79 #

While P0A79 is a generic code, it is most often reported on certain hybrid and electric vehicles with dual motor or advanced inverter systems. Brands and models frequently associated include:

• Toyota Prius (especially 3rd and 4th generation)
• Lexus CT200h, ES300h, and other Lexus hybrids
• Honda Accord Hybrid, Honda Insight
• Chevrolet Volt, Chevrolet Malibu Hybrid
• Ford Fusion Hybrid, Ford C-Max Hybrid
• Other OEM hybrid or electric models using similar inverter architectures

Common Mistakes & Best Practices for Code P0A79 #

Misdiagnosis and hasty repairs are unfortunately common with hybrid/electric faults. To avoid unnecessary expenses and further issues, keep these tips in mind:

• Do not replace the drive motor or inverter without confirming the root cause—always verify with OEM diagnostic procedures.
• Never work on high-voltage systems without proper training and safety equipment.
• Always check the inverter cooling circuit before assuming a hardware failure.
• Consult the latest Technical Service Bulletins (TSBs) for potential software or recall solutions.
• When in doubt, seek assistance from an OEM-certified hybrid/electric vehicle technician.

Express FAQ for Code P0A79 #

Here are quick answers to common questions regarding the P0A79 inverter performance code:

• Q: Can a simple coolant leak trigger P0A79?
  A: Yes—if the inverter cooling system is compromised, it can cause overheating and set this code, even if the inverter itself is still functional.
• Q: Is a software update ever the fix for P0A79?
  A: Occasionally—if the OEM has released updated control module software to better manage inverter performance, a reflash may resolve the issue.
• Q: Does clearing the code reset the system?
  A: Clearing the code may temporarily turn off the warning light, but if the underlying fault remains, the code will return almost immediately.