B1279

DTC Troubleshooting: B1279

DTC B1279: Headlight Switch DIMMER Position Circuit Malfunction

NOTE: If you are troubleshooting multiple DTCs, be sure to follow the instructions in B-CAN System Diagnosis Test Mode A. Troubleshooting - B-CAN System Diagnosis Test Mode A

1. Clear the DTCs with the HDS.

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

3. Turn the combination light (headlight) switch ON.

4. Change the dimmer switch from low beam to high beam.

5. Turn the combination light switch OFF, and then to the passing position, and wait for at least 6 seconds.

6. Check for DTCs with the HDS.

Is DTC B1279 indicated?
YES - Go to step 7.

NO - Intermittent failure, the system is OK at this time. Check for loose or poor connections.


7. Select LIGHTING from the BODY ELECTRICAL system select menu, then enter DATA LIST.

8. Check each combination light switch position value with the DATA LIST menu.

When the passing switch is operated





When the headlight switch is turned ON, and the dimmer switch changed from low beam to high beam





Are all data list values correct?
YES - Faulty MICU; replace the under-dash fuse/relay box. Under-Dash Fuse/Relay Box Removal and Installation

NO - Go to step 9.


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

10. Disconnect the combination light switch 12P connector.

11. Turn the ignition switch to ON (II).

12. Select LIGHTING from the BODY ELECTRICAL system select menu, then enter DATA LIST.

13. Check each combination light switch position value with the DATA LIST menu.

When the combination light switch is turned OFF





Are all data list values indicated OFF?
YES - Go to step 17.

NO - Go to step 14.


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

15. Disconnect under-dash fuse/relay box connector S (20P).

16. Check for continuity between body ground and under-dash fuse/relay box connector S (20P) terminals No. 11, No. 12, and No. 16. individually.

Is there continuity?
YES - Repair a short to ground in the wire.

NO - Faulty MICU; replace the under-dash fuse/relay box. Under-Dash Fuse/Relay Box Removal and Installation






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

18. Do the combination light switch test. Combination Light Switch Test/Replacement

Is the combination light switch OK?
YES - Go to step 19.

NO - Replace the combination light switch.


19. Disconnect under-dash fuse/relay box connector S (20P).

20. Check for continuity between under-dash fuse/relay box connector S (20P) terminals and the combination light switch 12P connector terminals as shown:





Is there continuity?
YES - Go to step 21.

NO - Repair an open in the wire.






21. Check for continuity between under-dash fuse/relay box connector S (20P) terminals as shown:





Is there continuity?
YES - Repair a short between the wires.

NO - Faulty MICU; replace the under-dash fuse/relay box. Under-Dash Fuse/Relay Box Removal and Installation