Check Headlight System

WARNING: This page is about a different car, the 2021 Subaru Ascent. However, it is still accessible from the selected car via links, so may be relevant.

Trouble symptom:

Headlight does not illuminate, or headlight is weak.

CHECK HEADLIGHT AND TAIL LIGHT ILLUMINATION .
1. Turn the ignition switch to ON.
2. Set the lighting switch to the switch 1 (TAIL/PARKING), switch 2 (HEAD) and switch UP.
Do the headlight (low beam), tail light and headlight (high beam) illuminate?

Yes : The headlight system is normal.

No : Go to 2.
CHECK CURRENT DATA .
Display the data of [LED HEADLAMP (RH) error Signal] and [LED HEADLAMP (LH) error Signal] using Subaru Select Monitor. Ref. to HEADLIGHT/FOGLIGHT (DIAGNOSTICS)>DATA MONITOR .

Is [Turn_ON] displayed?

Yes : Go to 3.

No : Replace the headlight assembly.
CHECK CONNECTOR CONNECTION .
Check that the headlight connector is connected.

Is the connector connected?

Yes : Go to 4.

No : Connect the connector.

When it does not illuminate even though the switch is turned to ON: Go to 4.
CHECK FUSE .
1. Turn the ignition switch to OFF.
2. Check the M/B fuses No. 6 and No. 7.
Is the check result OK?

Yes : Go to 5.

No : Replace the defective fuse.
CHECK HARNESS .
1. Disconnect the body integrated unit connector.
2. Using the tester, measure the voltage between terminals.
  Connector & terminal
  
  (B280) No. 3 (+) - Chassis ground (-):
  
  (B287) No. 3 (+) - Chassis ground (-):
Is the voltage 8.5 - 16.5 V?

Yes : Go to 6.

No : Repair the harness between body integrated unit and fuse.
CHECK HARNESS .
1. Disconnect the headlight connector.
2. Turn the ignition switch to ON.
3. Measure the voltage between the headlight connector and chassis ground.
  Connector & terminal
  
  RH side
  
  (B487) No. 1 (+) - Chassis ground (-):
  
  (B487) No. 2 (+) - Chassis ground (-):
  
  LH side
  
  (B477) No. 1 (+) - Chassis ground (-):
  
  (B477) No. 2 (+) - Chassis ground (-):
Is the voltage 10 - 13.5 V?

Yes : Go to 7.

No : Go to 8.
CHECK HEADLIGHT .
Apply battery voltage between headlight unit connector terminals.

Terminals

Low beam

No. 1 (+) - No. 4 (-):

High beam

No. 2 (+) - No. 4 (-):

Does the headlight (low beam and high beam) come on at normal brightness?

Yes : Go to 8.

No : Replace the headlight. Ref. to LIGHTING SYSTEM>HEADLIGHT ASSEMBLY .

Perform inspection for the malfunction signal line if the [LED HEADLAMP (RH) error Signal] and [LED HEADLAMP (LH) error Signal] do not illuminate in step 2). If short circuit to power supply occurs, repair or replace the harness.
CHECK CURRENT DATA .
1. Turn the ignition switch to ON.
2. Display the data of [Lighting I Switch Input], [Lighting II Switch Input] and [Dimmer Hi Switch Input] using Subaru Select Monitor.
  Ref. to BODY CONTROL (DIAGNOSTICS)>DATA MONITOR .
  - Do the displays of [Lighting I Switch Input] and [Lighting II Switch Input] switch between [OFF] <-> [ON] when the lighting switch is moved from OFF position to switch 1 (TAIL) and switch 2 (HEAD) positions?
  - Does the display of [Dimmer Hi Switch Input] switch between [OFF] <-> [ON] when the dimmer & passing switch is moved to the switch UP position?
Yes : Go to 11.

No : Go to 9.
CHECK COMBINATION SWITCH (LIGHT) .
1. Turn the ignition switch to OFF.
2. Check the combination switch (light).
  Ref. to LIGHTING SYSTEM>Combination Switch (Light)>INSPECTION .
Is the combination switch (light) normal?

Yes : Go to 10.

No : Replace the combination switch (light). Ref. to LIGHTING SYSTEM>Combination Switch (Light) .
CHECK HARNESS .
1. Disconnect the connector of body integrated unit.
2. Check the harness between body integrated unit and combination switch (light).
  Connector & terminal
  
  (i171) No. 35 - (i73) No. 18:
  
  (i171) No. 19 - (i73) No. 20:
  
  (i81) No. 28 - (i73) No. 20:
  
  (i171) No. 26 - (i73) No. 11:
Is harness normal?

Yes : Check the body integrated unit and replace it if defective.
- Inspection: Ref. to BODY CONTROL (DIAGNOSTICS)>BASIC DIAGNOSTIC PROCEDURE .
- Replacement: Ref. to SECURITY AND LOCKS>BODY INTEGRATED UNIT .
No : Repair or replace the harness.
CHECK CURRENT DATA .
1. Turn the ignition switch to ON.
2. Display the data of [Lighting I Lamp Output], [Lighting II Lamp Output] and [Lighting Hi Lamp Output] using Subaru Select Monitor.
  Ref. to BODY CONTROL (DIAGNOSTICS)>DATA MONITOR .
Do the displays of [Lighting I Lamp Output] and [Lighting II Lamp Output] switch between [OFF] <-> [ON] when the lighting switch is moved from OFF position to switch 1 (TAIL/PARKING) and switch 2 (HEAD) positions?

In addition, does the display of [Lighting Hi Lamp Output] switch between [OFF] <-> [ON] when the lighting switch is moved to the switch 2 (HEAD) position and the dimmer & passing switch to the switch UP position?

Yes : Go to 12.

No : Check the body integrated unit and replace it if defective.
- Inspection: Ref. to BODY CONTROL (DIAGNOSTICS)>BASIC DIAGNOSTIC PROCEDURE .
- Replacement: Ref. to SECURITY AND LOCKS>BODY INTEGRATED UNIT .
CHECK HARNESS .
1. Turn the ignition switch to OFF.
2. Disconnect the body integrated unit connector and the headlight and tail light connectors.
3. Check the harness between body integrated unit and headlight, tail light, and relay.
  Connector & terminal
  
  Headlight RH
  
  (B280) No. 9 - (B487) No. 2:
  
  Headlight LH
  
  (B287) No. 7 - (B477) No. 2:
  
  Tail light RH
  
  (B280) No. 10 - (R266) No. 1:
  
  Tail light LH
  
  (B280) No. 10 - (R208) No. 1:
  
  Relay
  
  H/L LO relay No. 2 - (B287) No. 6:
  
  H/L LO relay No. 2 - (i171) No. 23:
  
  H/L LO relay No. 4 - (B281) No. 20:
  
  H/L LO relay No. 4 - (i171) No. 18:
Is harness normal?

Yes : Check the body integrated unit and replace it if defective.
- Inspection: Ref. to BODY CONTROL (DIAGNOSTICS)>BASIC DIAGNOSTIC PROCEDURE .
- Replacement: Ref. to SECURITY AND LOCKS>BODY INTEGRATED UNIT .
No : Repair or replace the harness.