DTC Troubleshooting: B121B (H and A/C ON)
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.
  1. Turn the ignition switch to LOCK (0) and then to ON (II).
  1. Do the self-diagnostic function with the HDS or the heater control unit.
  1. Check for DTCs.
Is DTC B121B or H and A/C ON indicated?
YES -
Go to Step 5 .
NO -
Intermittent failure.■
  1. 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 .
  1. Turn the ignition switch to LOCK (0).
  1. Test the mode control motor.
Is the mode control motor OK?
YES -
Go to Step 8 .
NO -
Replace the mode control motor. ■
  1. Disconnect the mode control motor 7P connector.
  1. Disconnect heater control unit connectors A (28P) and B (12P).
  1. Check for continuity between body ground and heater control unit connector A (28P) No. 11 terminal.
Is there continuity?
YES -
Repair short to body ground in the wire between the heater control unit and the mode control motor.■
NO -
Go to Step 11 .