Manufacturer Code Charts: 12

HVAC DTC Troubleshooting: 12

DTC indicator 12: A Problem in the Blower Motor Circuit

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

2. Do the self-diagnostic function with the HVAC control unit. How to Troubleshoot the Heating and A/C Systems

3. Check for DTCs.

Is DTC 12 indicated?
YES - Go to step 4.

NO - Intermittent failure, check for loose wires or poor connections on the blower motor circuit.


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

5. Check the No. 8 (40 A) fuse in the under-hood fuse/relay box, and the No. 16 (7.5 A) fuse in the driver's under-dash fuse/relay box.

Are the fuses OK?
YES - Go to step 6.

NO - Replace the fuse(s), and recheck. If the fuse(s) blow again, check for a short in the No. 8 (40 A) fuse and the No. 16 (7.5 A) fuse circuits.


6. Connect the blower motor 2P connector No. 2 terminal to body ground with a jumper wire.

7. Turn the ignition switch to ON (II).

Does the blower motor run?
YES - Go to step 8.

NO - Go to step 23.






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

9. Disconnect the jumper wire.

10. Disconnect the power transistor 4P connector.

11. Check for continuity between the power transistor 4P connector No. 2 terminal and body ground.

Is there continuity?
YES - Go to step 12.

NO - Check for an open in the wire between the power transistor and body ground If the wire is OK, check for poor ground at G302.






12. Connect the power transistor 4P connector No. 2 and No. 4 terminals with a jumper wire.

13. Turn the ignition switch to ON (II).

Does the blower motor run at high speed?
YES - Go to step 14.

NO - Repair open in the GRN wire between the power transistor and the blower motor.






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

15. Disconnect the jumper wire.

16. Disconnect the HVAC control unit 24P connector.

17. Check for continuity between body ground and the HVAC control unit 24P connector No. 18 and No. 19 terminals individually.

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

NO - Go to step 18.






18. Check for continuity between the following terminals of the HVAC control unit 24P connector and the power transistor 4P connector.





Is there continuity?
YES - Go to step 19.

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






19. Turn the ignition switch to ON (II).

20. Measure the voltage between body ground and the HVAC control unit 24P connector No. 18 and No. 19 terminals individually.

Is there any voltage?
YES - Repair short to power in the wires.

NO - Go to step 21.






21. Reconnect the HVAC control unit 24P connector.

22. Test the power transistor. Blower Power Transistor Test

Is the power transistor OK?
YES - Check for loose wires or poor connections at the HVAC control unit 24P connector, and at the power transistor 4P connector. If the connections are good, substitute a known-good HVAC control unit, and recheck. If the symptom/indication goes away, replace the original HVAC control unit.

NO - Replace the power transistor.


23. Disconnect the jumper wire.

24. Disconnect the blower motor 2P connector.

25. Measure the voltage between the blower motor 2P connector No. 1 terminal and body ground.

Is there battery voltage?
YES - Replace the blower motor. Blower Unit Component Replacement

NO - Go to step 26.






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

27. Remove the blower motor relay from the under-hood fuse/relay box, and test it. Testing and Inspection

Is the relay OK?
YES - Go to step 28.

NO - Replace the blower motor relay.


28. Measure the voltage between the blower motor relay 4P socket No. 1 terminal and body ground.

Is there battery voltage?
YES - Go to step 29.

NO - Replace the under-hood fuse/relay box. Under-Hood Fuse/Relay Box Removal and Installation






29. Turn the ignition switch to ON (II).

30. Measure the voltage between the blower motor relay 4P socket No. 4 terminal and body ground.

Is there battery voltage?
YES - Go to step 31.

NO - Repair open in the wire between the No. 16 (7.5 A) fuse in the driver's under-dash fuse/relay box and the blower motor relay.






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

32. Check for continuity between the blower motor relay 4P socket No. 3 terminal and body ground.

Is there continuity?
YES - Repair open in the WHT wire between the blower motor relay and the blower motor.

NO - Check for an open in the wire between the blower motor relay and body ground If the wire is OK, check for poor ground at G301.