B1279

DTC Troubleshooting: B1279

DTC B1279:

Dimmer Switch 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.

6. Wait for at least 6 seconds.

7. Check for DTCs with the HDS.

Is DTC B1279 indicated?

YES -

Go to step 8.

NO -

Intermittent failure, the system is OK at this time. Check for loose or poor connections between the driver's under-dash fuse/relay box and the combination light switch.

8. Select LIGHTING from the BODY ELECTRICAL SYSTEM SELECT menu, then enter the DATA LIST.

9. 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 driver's under-dash fuse/relay box, USA models Drivers Under-Dash Fuse/Relay Box (Drivers MICU) Removal And Installation (USA Model), Canada models Drivers Under-Dash Fuse/Relay Box (Drivers MICU) Removal And Installation (Canada Model).

NO -

Go to step 10.

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

11. Disconnect the combination light switch 12P connector.

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

13. Select LIGHTING from the BODY ELECTRICAL SYSTEM SELECT menu, then enter the DATA LIST.

14. 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 18.

NO -

Go to step 15.

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

16. Disconnect under-dash fuse/relay box connector P (24P).

17. Check for continuity between body ground and driver's under-dash fuse/relay box connector P (24P) terminals No. 15, No. 20, and No. 21 individually.





Is there continuity?

YES -

Repair a short to ground in the wire(s).

NO -

Faulty MICU; replace the driver's under-dash fuse/relay box, USA models Drivers Under-Dash Fuse/Relay Box (Drivers MICU) Removal And Installation (USA Model), Canada models Drivers Under-Dash Fuse/Relay Box (Drivers MICU) Removal And Installation (Canada Model).

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

19. Do the combination light switch test.

Is the combination light switch OK?

YES -

Go to step 20.

NO -

Replace the combination light switch.

20. Disconnect driver's under-dash fuse/relay box connector P (24P).

21. Check for continuity between driver's under-dash fuse/relay box connector P (24P) terminals and the combination light switch 12P connector terminals as shown:









Is there continuity?

YES -

Go to step 22.

NO -

Repair an open or high resistance in the wire(s).

22. Check for continuity between driver's under-dash fuse/relay box connector P (24P) terminals as shown:





Is there continuity?

YES -

Repair a short between the wires.

NO -

Faulty MICU; replace the driver's under-dash fuse/relay box, USA models Drivers Under-Dash Fuse/Relay Box (Drivers MICU) Removal And Installation (USA Model), Canada models Drivers Under-Dash Fuse/Relay Box (Drivers MICU) Removal And Installation (Canada Model).