A And WINDSHIELD DEFROST
DTC Troubleshooting: B121D (A and WINDSHIELD DEFROST)
DTC B121D or DTC indicator A and WINDSHIELD DEFROST:
Humidity/in-car temperature Sensor Communication Error (An Open or Short in the Humidity Sensor Circuit)
1. Clear the DTCs 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 B121D or A and WINDSHIELD DEFROST indicated?
YES -
Go to step 5.
NO -
Intermittent failure. Check for loose wires or poor connections on the humidity sensor circuit.
5. Check for DTCs.
Are these DTCs also present; B1234 or C and WINDSHIELD DEFROST, and/or B1237 or F and WINDSHIELD DEFROST, and/or B2980 or M and AUTO?
YES -
Go to step 14.
NO -
Go to step 6.
6. Turn the ignition switch to LOCK (0).
7. Remove the humidity/in-car temperature sensor Service and Repair, and test it Testing and Inspection.
Is the humidity sensor OK?
YES -
Go to step 8.
NO -
Replace the humidity/in-car temperature sensor Service and Repair.
8. Disconnect the humidity/in-car temperature sensor 4P connector.
9. Disconnect climate control unit connector A (36P).
10. Check for continuity between the following terminals of climate control unit connector A (36P) and the humidity/in-car temperature sensor 4P connector.
Is there continuity?
YES -
Check for loose wires or poor connections at climate control unit connectors A (36P) and at the humidity/in-car temperature sensor 4P connector. If the connections are good, go to step 11.
NO -
Repair an open in the wire(s) between the climate control unit and the humidity sensor.
11. Check for continuity between climate control unit connector A (36P) terminal No. 3 and body ground.
Is there continuity?
YES -
Repair a short to body ground in the wire between the climate control unit and the humidity sensor.
NO -
Go to step 12.
12. Check for continuity between climate control unit connector A (36P) terminals No. 2 and No. 3.
Is there continuity?
YES -
Repair a short in the wire(s).
NO -
Go to step 13.
13. Turn the ignition switch to ON (II), and measure the voltage between climate control unit connector A (36P) terminal No. 3 and body ground.
Is there any voltage?
YES -
Repair a short to power in the wire between the climate control unit and the humidity sensor. 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.
14. Turn the ignition switch to LOCK (0), and disconnect climate control unit connector A (36P).
15. Disconnect these items:
- Driver's air mix control motor
- Passenger's air mix control motor
- Humidity/in-car temperature sensor
- A/C pressure sensor
- Rear air mix control motor
16. Check for continuity between climate control unit connector A (36P) terminal No. 2 and body ground.
Is there continuity?
YES -
Repair a short to body ground in the wire.
NO -
Go to step 17.
17. Turn the ignition switch to ON (II), and measure the voltage between the same terminal and body ground.
Is there any voltage?
YES -
Repair a short to power in the wire. This short may have also damaged the climate control unit. Repair a short to power before replacing the climate control unit.
NO -
Go to step 18.
18. Turn the ignition switch to LOCK (0).
19. Reconnect climate control unit connector A (36P).
20. Turn the ignition switch to ON (II), and measure the voltage between climate control unit connector A (36P) terminal No. 2 and body ground.
Is there about 5 V?
YES -
Go to step 21.
NO -
Check for a loose wire or poor connection at climate control unit connector A (36P). 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.
21. While measuring the voltage between the same terminal 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
- Humidity/in-car temperature sensor
- A/C pressure sensor
- Rear air mix 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.