H and A/C

DTC Troubleshooting: B121B (H and A/C)

DTC B121B or DTC indicator H and A/C ON:

A Short in the Mode Control Motor Circuit

1. Clear the DTC with the HDS.

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

3. Do the Self-Diagnostic Function with the HDS or the climate control unit.

4. Check for DTCs.

Is DTC B121B or H and A/C ON indicated?

YES -

Go to step 5.

NO -

Intermittent failure. Check for loose wires or poor connections on the mode control motor circuit.

5. Check for DTCs.

Are these DTCs also present; B1220 or L and A/C ON, and/or B1234 or B and A/C ON, and/or B1237 or E and A/C ON?

YES -

Go to step 13.

NO -

Go to step 6.

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

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

Is the mode control motor OK?

YES -

Go to step 8.

NO -

Replace the mode control motor Mode Control Motor Replacement.

8. Disconnect the mode control motor 7P connector.

9. Disconnect climate control unit connectors A (28P) and B (12P).

10. Check for continuity between climate control unit connector A (28P) terminal No. 11 and body ground.





Is there continuity?

YES -

Repair a short to body ground in the wire between the climate control unit and the mode control motor.

NO -

Go to step 11.

11. Check for continuity between climate control unit connector A (28P) terminal No. 11 and climate control unit connector B (12P) terminal No. 12.





Is there continuity?

YES -

Repair a short in the wires between the climate control unit and the mode control motor.

NO -

Go to step 12.

12. Turn the ignition switch to ON (II), and measure the voltage between climate control unit connector A (28P) terminal No. 11 and body ground.





Is there any voltage?

YES -

Repair a short to power in the wire between the climate control unit and the mode control motor. This short may also damage the climate control unit. Repair a short to power before replacing the climate control unit.

NO -

Substitute a known-good climate control unit, and recheck. If the symptom/indication goes away, replace the original climate control unit Climate Control Unit Removal/Installation.

13. Turn the ignition switch to LOCK (0), and disconnect climate control unit connector B (12P).

14. Disconnect these items:

- Driver's air mix control motor
- Passenger's air mix control motor
- Recirculation control motor
- Mode control motor

15. Check for continuity between climate control unit connector B (12P) terminal No. 12 and body ground.





Is there continuity?

YES -

Repair a short to body ground in the wire between the climate control unit and the mode control motor.

NO -

Go to step 16.

16. Turn the ignition switch to ON (II), and measure the voltage between climate control unit connector B (12P) terminal No. 12 and body ground.





Is there any voltage?

YES -

Repair a short to power in the wire between the climate control unit and the mode control motor. This short may have also damaged the climate control unit. Repair short to power before replacing the climate control unit.

NO -

Go to step 17.

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

18. Reconnect climate control unit connector B (12P).

19. Turn the ignition switch to ON (II), and measure the voltage between climate control unit connector B (12P) terminal No. 12 and body ground.





Is there about 5 V?

YES -

Go to step 20.

NO -

Check for loose wires or poor connections at climate control unit connector B (12P). If the connection is good, substitute a known-good climate control unit, and recheck. If the symptom/indication goes away, replace the original climate control unit Climate Control Unit Removal/Installation.

20. While measuring the voltage between climate control unit connector B (12P) terminal No. 12 and body ground, reconnect these items individually and note the voltage reading each time:

- Driver's air mix control motor
- Passenger's air mix control motor
- Recirculation control motor
- Mode control motor





Does the voltage remain at about 5 V?

YES -

Substitute a known-good climate control unit, and recheck. If the symptom/indication goes away, replace the original climate control unit Climate Control Unit Removal/Installation.

NO -

Replace the component that caused the voltage drop.