WOMS
P code powertrain Medium severity

P28AC Transmission Control Module (TCM) Performance

The OBD2 code P28AC indicates that the Transmission Control Module (TCM) is experiencing performance issues, suggesting that it is not operating within the expected parameters or is failing to communicate properly with...

Definition

The OBD2 code P28AC indicates that the Transmission Control Module (TCM) is experiencing performance issues, suggesting that it is not operating within the expected parameters or is failing to communicate properly with other vehicle systems

Common causes

  • Faulty Transmission Control Module (TCM)
  • Wiring issues or damaged connectors
  • Low transmission fluid levels
  • Contaminated or degraded transmission fluid
  • Faulty transmission sensors (e.g., speed sensors)
  • Software issues or outdated TCM programming
  • Mechanical transmission problems
  • Electrical issues, such as short circuits or open circuits in the TCM circuit

Common misdiagnoses

  • Faulty Transmission Control Module (TCM)
  • Wiring issues or short circuits
  • Faulty sensors (e.g., speed sensors)
  • Low transmission fluid levels
  • Transmission fluid contamination
  • Mechanical transmission issues
  • Engine control module (ECM) problems
  • Incorrectly calibrated transmission
  • Software issues or outdated firmware
  • Electrical connector problems

Troubleshooting steps

  1. 1. Check for Additional Codes

    Use an OBD-II scanner to check for any other related trouble codes. Sometimes, multiple codes can provide more context for the issue

  2. 2. Inspect Wiring and Connectors

    Examine the wiring and connectors related to the TCM for any signs of damage, corrosion, or loose connections. Pay special attention to the harness that connects to the TCM

  3. 3. Check TCM Power and Ground

    Ensure that the TCM is receiving the proper power and ground signals. Use a multimeter to check voltage and ground continuity

  4. 4. Inspect Transmission Fluid

    Check the transmission fluid level and condition. Low or dirty fluid can cause performance issues. If the fluid is burnt or contaminated, consider a fluid change

  5. 5. Test the TCM

    If the wiring and connections are good, the TCM itself may be faulty. Testing the TCM may require specialized equipment or professional assistance

  6. 6. Check for Mechanical Issues

    Inspect the transmission for any mechanical problems, such as slipping gears, which could affect TCM performance. Look for signs of wear or damage in the transmission components

  7. 7. Update or Reprogram TCM

    Sometimes, the TCM may need to be updated or reprogrammed. Check with the manufacturer for any software updates or recalls related to the TCM

  8. 8. Clear Codes and Test Drive

    After performing any repairs or adjustments, clear the trouble codes and take the vehicle for a test drive to see if the code returns

  9. 9. Consult Technical Service Bulletins (TSBs)

    Check for any TSBs related to the specific make and model of the vehicle. Manufacturers often release TSBs for known issues that can provide guidance on troubleshooting and repairs

  10. 10. Seek Professional Help

    If the issue persists after performing the above steps, it may be necessary to consult a professional mechanic or transmission specialist for further diagnosis. By following these steps, you can systematically identify and address the cause of the P28AC code