B121D

Control System DTCs

DTC Troubleshooting: B121D - (89)

DTC B121D or DTC indicator 89 : Humidity/In-Car Temperature Sensor Communication Error

1. Problem verification:

Problem verification
-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 with the HDS or the climate control unit How To Troubleshoot The Climate Control System.

-4. Check for DTCs.

Is DTC B121D or 89 indicated?
-YES- Go to step 2.
-NO- Intermittent failure.

2. Humidity/in-car temperature sensor S_5V line check:

Humidity/in-car temperature sensor S_5V line check
-1. Turn the ignition switch to LOCK (0).

-2. Disconnect the following connector.





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

-4. Measure the voltage between test points 1 and 2.









Is there about 5 V?
-YES- Go to step 3.
-NO- Go to step 7.

3. Open wire check (SENSOR_COM line):

Open wire check (SENSOR_COM line)
-1. Turn the ignition switch to LOCK (0).

-2. Disconnect the following connector.





-3. Check for continuity between test points 1 and 2.









Is there continuity?
-YES- The SENSOR_COM wire is OK. Go to step 4.
-NO- Repair an open in the wire between the climate control unit and the humidity/in-car temperature sensor.

4. Climate control unit HUM_DATA, TR lines check:

Climate control unit HUM_DATA, TR lines check
-1. Connect terminals A and B with a jumper wire.









-2. Check for continuity between test points 1 and 2.









Is there continuity?
-YES- Go to step 5.
-NO- Go to step 8.

5. Climate control unit HUM_DATA line check:

Climate control unit HUM_DATA line check
-1. Check for continuity between test points 1 and 2.









Is there continuity?
-YES- Go to step 6.
-NO- Go to step 9.

6. Shorted wire check (HUM_DATA line):

Shorted wire check (HUM_DATA line)
-1. Disconnect the jumper wire.

-2. Check for continuity between test points 1 and 2.









Is there continuity?
-YES- Repair a short to body ground in the YEL wire between the climate control unit and the humidity/in-car temperature sensor.
-NO- Repair a short to body ground in the LT BLU wire between the climate control unit and the humidity/in-car temperature sensor.

7. Open wire check (S_5V line):

Open wire check (S_5V line)
-1. Turn the ignition switch to LOCK (0).

-2. Disconnect the following connector.





-3. Check for continuity between test points 1 and 2.









Is there continuity?
-YES- Repair a short in the wires between the climate control unit and the humidity/in-car temperature sensor.
-NO- Repair an open in the wire between the climate control unit and the humidity/in-car temperature sensor.

8. Open wire check (HUM_DATA line):

Open wire check (HUM_DATA line)
-1. Disconnect the jumper wire.

-2. Check for continuity between test points 1 and 2.









Is there continuity?
-YES- Repair an open in the LT BLU wire between the climate control unit and the humidity/in-car temperature sensor.
-NO- Repair an open in the YEL wire between the climate control unit and the humidity/in-car temperature sensor.

9. Shorted wire check (HUM_DATA, TR lines):

Shorted wire check (HUM_DATA, TR lines)
-1. Disconnect the jumper wire.

-2. Check for continuity between test points 1 and 2.









Is there continuity?
-YES- Repair a short in the wires between the climate control unit and the humidity/in-car temperature sensor.
-NO- Go to step 10.

10. Climate control unit check:

Climate control unit check
-1. Reconnect the climate control unit 32P connector.

-2. Connect terminals A and B with a jumper wire.









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

-4. Press and hold the AUTO and ON/OFF buttons.





Does the mode indicator turn on?
-YES- Replace the humidity/in-car temperature sensor Service and Repair.
-NO- Replace the climate control unit.