Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
DTC P0A1B (84): Motor Control Module (MCM) Internal Circuit Malfunction
- Before you troubleshoot, record all freeze data and any on-board snapshot, and review the general troubleshooting information (see GENERAL TROUBLESHOOTING INFORMATION ).
- If the DTC cannot be cleared, do the troubleshooting for DTC U1204 (55).
- Turn the ignition switch to ON (II).
- Clear the DTC with the HDS (see DTC CLEAR ).
- Turn the ignition switch to LOCK (0), and wait 1 minute.
- Turn the ignition switch to ON (II).
- Check for Pending or Confirmed DTCs with the HDS.
Is DTC P0A1B (84) indicated?
YES -go to step 6.
NO -Intermittent failure, the system is OK at this time.
- Update the MCM if it does not have the latest software (see MOTOR CONTROL MODULE (MCM) UPDATE ), or substitute a known-good MCM (see SUBSTITUTING THE MCM ).
- Turn the ignition switch to LOCK (0), and wait 1 minute.
- Turn the ignition switch to ON (II).
- Check for Pending or Confirmed DTCs with the HDS.
Is DTC P0A1B (84) indicated?
YES -If the MCM was updated, substitute a known-good MCM (see SUBSTITUTING THE MCM ), and recheck. If the MCM was substituted, go to step 1.
NO -go to step 10.
- Monitor the OBD STATUS for DTC P0A1B (84) in the DTCs MENU with the HDS.
Does the screen indicate PASSED?
YES -If the MCM was updated, troubleshooting is complete. If the MCM was substituted, replace the original MCM (see MOTOR CONTROL MODULE (MCM) REMOVAL/INSTALLATION ). If any other Pending or Confirmed DTCs were indicated in step 9, go to the indicated DTC's troubleshooting.
NO -
- If the screen indicates FAILED: If the MCM was updated, substitute a known-good MCM (see SUBSTITUTING THE MCM ), and recheck. If the MCM was substituted, go to step 1.
- If the screen indicates NOT COMPLETED: Keep the ignition switch ON (II) until a result comes on.
NO RELATED
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.