Auto Headlight System Check

WARNING: This page is about a different car, the 2023 Subaru Ascent. However, it is still accessible from the selected car via links, so may be relevant.

Wiring diagram:

Headlight system and daytime running light system Ref. to WIRING SYSTEM>HEADLIGHT SYSTEM AND DAYTIME RUNNING LIGHT SYSTEM>WIRING DIAGRAM .

Courtesy of SUBARU OF AMERICA, INC.

NOTE: Check the headlight system before checking the auto headlight system. Ref. to LIGHTING SYSTEM>HEADLIGHT SYSTEM>INSPECTION>CHECK HEADLIGHT SYSTEM .

CHECK HEADLIGHT AND TAIL LIGHT ILLUMINATION .
1. Turn the ignition switch to ON.
2. Make the light control sensor vicinity dark.
3. Set the lighting switch to AUTO position.
4. Make the light control sensor vicinity bright.
5. Turn the lighting switch to the OFF position and turn to the AUTO position again. (U4 model)
6. Operate the lighting switch from AUTO position to OFF position twice. (Except for U4 model)
Do the parking light, headlight and tail light illuminate?

Yes: The auto headlight system is normal.

No: Go to 2.
CHECK CURRENT DATA .
1. Display the [Illumination Sensor Output] data using Subaru Select Monitor. Ref. to BODY CONTROL (DIAGNOSTICS)>DATA MONITOR .
2. Measure the voltage when the area around the light control sensor, which was dark, becomes bright.
Illumination sensor output

Dark condition: Approx. 0.6 V or less

Bright condition: Approx. 3 V or more

Is the voltage output according to the brightness?

Yes: Go to 5.

No: Go to 3.
CHECK LIGHT CONTROL SENSOR .
Check the light control sensor. Ref. to LIGHTING SYSTEM>LIGHT CONTROL SENSOR>INSPECTION .

Is the light control sensor normal?

Yes: Go to 4.

No: Replace the light control sensor.
CHECK HARNESS .
1. Disconnect the connectors from body integrated unit and light control sensor.
2. Check the harness between body integrated unit and light control sensor.
  Connector & terminal
  
  (i171) No. 8 - (i89) No. 1:
  
  (i171) No. 28 - (i89) No. 2:
  
  (i171) No. 34 - (i89) No. 3:
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 .
- U4 model: Display the [Lighting AUTO input] data using Subaru Select Monitor. Ref. to BODY CONTROL (DIAGNOSTICS)>DATA MONITOR .
- Except for U4 model: Display the [Lighting OFF Switch Input] data using Subaru Select Monitor. Ref. to BODY CONTROL (DIAGNOSTICS)>DATA MONITOR .
- U4 model: Does the display switch between [OFF] ←→ [ON] when the lighting switch is moved from the OFF position to the AUTO position?
- Except for U4 model: Does the display change as [OFF] ←→ [ON] when the lighting switch is moved from the AUTO position to the OFF position?
Yes: Go to 6.

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 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 7.

No: Replace the combination switch (light).
CHECK HARNESS .
1. Disconnect the connectors of body integrated unit and combination switch (light).
2. Check the harness between body integrated unit and combination switch (light).
  Connector & terminal
  
  U4 model
  
  (i73) No. 19 - (i81) No. 20:
  
  Except for U4 model
  
  (i73) No. 18 - (i81) No. 20:
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.