HVAC - With A/C

HVAC DTC Troubleshooting: 3

DTC 3: A Problem in the Blower Motor Circuit

1. Check the No. 56 (40 A) fuse in the main under-hood fuse/relay box, and the No. 20 (7.5 A) fuse in the under-dash fuse/relay box.

Are the fuses OK?
YES - Go to step 2.

NO - Replace the fuse(s), and recheck. If the fuse(s) blow again, check for a short in the No. 56 (40 A) and the No. 20 (7.5 A) fuse circuits.


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

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

Does the blower motor run?
YES - Go to step 4.

NO - Go to step 17.






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

5. Disconnect the jumper wire.

6. Disconnect the power transistor 5P connector.

7. Check for continuity between power transistor 5P connector terminal No. 5 and body ground.

Is there continuity?
YES - Go to step 8.

NO - Check for an open in the wire between the power transistor and body ground. If the wire is OK, check for poor body ground at G402.






8. Connect power transistor 5P connector terminals No. 4 and No. 5 with a jumper wire.

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

Does the blower motor run at high speed?
YES - Go to step 10.

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






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

11. Disconnect the jumper wire.

12. Disconnect the HVAC control unit 30P connector.

13. Check for continuity between HVAC control unit 30P connector terminals No. 11 and No. 13 and body ground 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 14.






14. Check for continuity between the following terminals of the HVAC control unit 30P connector and the power transistor 5P connector.





Is there continuity?
YES - Go to step 15.

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






15. Reconnect the HVAC control unit 30P connector.

16. 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 30P connector, the blower motor 2P connector, and at the power transistor 5P 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.


17. Disconnect the jumper wire.

18. Disconnect the blower motor 2P connector.

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

Is there battery voltage?
YES - Replace the blower motor.

NO - Go to step 20.






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

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

Is the relay OK?
YES - Go to step 22.

NO - Replace the blower motor relay.


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

Is there battery voltage?
YES - Go to step 23.

NO - Replace the main under-hood fuse/relay box. Service and Repair






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

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

Is there battery voltage?
YES - Go to step 25.

NO - Repair open in the wire between the No. 20 (7.5 A) fuse in the under-dash fuse/relay box and the blower motor relay.






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

26. Check for continuity between blower motor relay 4P socket terminal No. 2 and body ground.

Is there continuity?
YES - Repair open in the 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 body ground at G201.