( TF09E00K763000Y1278FAAT00 )
DTC Troubleshooting: B1278
DTC B1278:
 Headlight ON Position Circuit Malfunction
  1. Clear the DTCs with the HDS.
  1. Turn the ignition switch to LOCK (0), and then back to ON (II).
  1. Operate each combination light switch position, then turn the combination light switch OFF.
  1. Check for DTCs with the HDS.
Is DTC B1278 indicated?
YES -
Go to Step 5 .
NO -
Intermittent failure, the system is OK at this time. Check for loose or poor connections.■
  1. Select LIGHTING from the BODY ELECTRICAL system select menu.
  1. Check each combination light switch position value with the DATA LIST menu.

    When the combination light switch turns OFF:

    Data List
    Value
    Headlight Switch (OFF)
    ON
    Headlight Switch (PARKING)
    OFF
    Headlight Switch (HEADLIGHT)
    OFF


    When the combination light switch turns SMALL:

    Data List
    Value
    Headlight Switch (OFF)
    OFF
    Headlight Switch (PARKING)
    ON
    Headlight Switch (HEADLIGHT)
    OFF


    When the combination light switch turns ON (headlight):

    Data List
    Value
    Headlight Switch (OFF)
    OFF
    Headlight Switch (PARKING)
    ON
    Headlight Switch (HEADLIGHT)
    ON

Are all data list values correct?
YES -
NO -
Go to Step 7 .
  1. Turn the ignition switch to LOCK (0).
  1. Disconnect the combination light switch 12P connector.
  1. Turn the ignition switch to ON (II).
  1. Select LIGHTING from the BODY ELECTRICAL system select menu.
  1. Check each combination light switch position value with the DATA LIST menu.

    When the combination light switch is OFF:

    Data List
    Value
    Headlight Switch (OFF)
    OFF
    Headlight Switch (PARKING)
    OFF
    Headlight Switch (HEADLIGHT)
    OFF

Are all data list values indicated OFF?
YES -
Go to Step 15 .
NO -
Go to Step 12 .
  1. Turn the ignition switch to LOCK (0).
  1. Disconnect under-dash fuse/relay box connector M (34P).
  1. Check for continuity between under-dash fuse/relay box connector M (34P) No. 5, No. 7, and No. 8 terminals and body ground individually.
Is there continuity?
YES -
Repair a short to ground in the wire.■
NO -
  1. Turn the ignition switch to LOCK (0).
Is the combination light switch OK?
YES -
Go to Step 17 .
NO -
Replace the combination light switch.■
  1. Disconnect under-dash fuse/relay box connector M (34P).
  1. Check for continuity between under-dash fuse/relay box connector M (34P) terminals and the combination light switch 12P connector terminals as shown:
    Under-dash fuse/relay box connector M (34P)
    Combination light switch 12P connector
    5
    9 [10]
    7
    8 [11]
    8
    10[9]
    33
    7[12]

    [ ]:
    LHD model

Is there continuity?
YES -
NO -
Repair an open in the wire.■
RHD model
LHD model