B121B

Control System DTCs

DTC Troubleshooting: B121B - (4A)

DTC B121B or DTC indicator 4A : A Short in the Mode Control Motor Circuit

1. Problem verification:

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

-4. Check for DTCs.

Is DTC B121B or 4A indicated?
-YES- Go to step 2.
-NO- Intermittent failure. Check for loose wires or poor connections on the mode control motor circuit.

2. DTC check:

DTC check
-1. Turn the ignition switch to LOCK (0).

-2. Disconnect the following connector.





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

-4. Do the self-diagnostic with the HDS or the climate control unit How To Troubleshoot The Climate Control System.

-5. Check for DTCs with the HDS.

Is DTC B121B or 4A indicated?
-YES- Go to step 3.
-NO- Replace the mode control motor Mode Control Motor Removal and Installation.

3. Mode control motor S5V line check:

Mode control motor S5V line check
-1. Measure the voltage between test points 1 and 2.









Is there 5 V?
-YES- Go to step 4.
-NO- Go to step 5.

4. Shorted wire check (MDD-P line):

Shorted wire check (MDD-P 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 wire between the climate control unit and the mode control motor.
-NO- The MDD-P wire is OK. Replace the climate control unit.

5. Shorted wire check (S_5V line):

Shorted 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 wire between the climate control unit and the mode control motor.
-NO- The S_5V wire is OK. Replace the climate control unit.