HVAC - With A/C

HVAC DTC Troubleshooting: 4

DTC indicator 4: An Open or Short in the Mode Control Motor Circuit

1. Turn the ignition switch to LOCK (0), and then turn it to ON (II).

2. Do the self-diagnostic with the HVAC control unit. How To Troubleshoot The Heating and A/C Systems (With A/C)

3. Check for DTCs.

Is DTC 4 indicated?
YES - Go to step 4.

NO - Intermittent failure. Check for loose wires or poor connections on the mode control motor circuit.


4. Turn the ignition switch to LOCK (0).

5. Test the mode control motor. Mode Control Motor Test

Is the mode control motor OK?
YES - Go to step 6.

NO - Replace the mode control motor Mode Control Motor Replacement.


6. Disconnect the mode control motor 7P connector.

7. Disconnect the HVAC control unit 24P connector.

8. Check for continuity between the following terminals of the HVAC control unit 24P connector and the mode control motor 7P connector.





Is there continuity?
YES - Go to step 9.

NO - Repair open in the wire(s) between the HVAC control unit and the mode control motor.






9. Check for continuity between body ground and the HVAC control unit 24P connector terminals No. 3, 4, 5, 6, and 13 individually.

Is there continuity?
YES - Repair short to body ground in the wire(s) between the HVAC control unit and the mode control motor.

NO - Go to step 10.






10. Check for continuity between the HVAC control unit 24P connector terminals as follows.





Is there continuity between any of the terminals?
YES - Repair short in the wires.

NO - Go to step 11.


11. Turn the ignition switch to ON (II), and measure the same terminals for voltage between each terminal and body ground.

Is there any voltage?
YES - Repair short to power in the wire(s) between the HVAC control unit and the mode control motor. This short may also damage the HVAC control unit. Repair the short to power before replacing the HVAC control unit.

NO - Check for loose wires or poor connections at the HVAC control unit 24P connector and at the mode control motor 7P connector. If the connections are good, substitute a known-good HVAC control unit Service and Repair, and recheck. If the symptom/indication goes away, replace the original HVAC control unit.