Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
2021 Subaru Ascent BaseFACTORY OEM SERVICE PROCEDURE
Exterior Lights System DTCS
EXTERIOR LIGHTS SYSTEM DIAGNOSTIC TROUBLE CODE (DTC) IDENTIFICATION
| Code | Reference |
|---|---|
| B2900 | Ref. to HEADLIGHT/FOGLIGHT (DIAGNOSTICS)>Diagnostic Procedure with Diagnostic Trouble Code (DTC)>DTC B2900 AHL CONTROL . |
| B2904 | Ref. to HEADLIGHT/FOGLIGHT (DIAGNOSTICS)>Diagnostic Procedure with Diagnostic Trouble Code (DTC)>DTC B2904 LED HEADLIGHT CIRCUIT RH . |
| B2905 | Ref. to HEADLIGHT/FOGLIGHT (DIAGNOSTICS)>Diagnostic Procedure with Diagnostic Trouble Code (DTC)>DTC B2905 LED HEAD LIGHT CIRCUIT LH . |
| B2908 | Ref. to HEADLIGHT/FOGLIGHT (DIAGNOSTICS)>Diagnostic Procedure with Diagnostic Trouble Code (DTC)>DTC B2908 STEERING RESPONSIVE HEADLIGHT ACTUATOR RH . |
| B2909 | Ref. to HEADLIGHT/FOGLIGHT (DIAGNOSTICS)>Diagnostic Procedure with Diagnostic Trouble Code (DTC)>DTC B2909 STEERING RESPONSIVE HEADLIGHT ACTUATOR LH . |
| B2910 | Ref. to HEADLIGHT/FOGLIGHT (DIAGNOSTICS)>Diagnostic Procedure with Diagnostic Trouble Code (DTC)>DTC B2910 STEERING RESPONSIVE HEADLIGHT COMMUNICATION RH . |
| B2911 | Ref. to HEADLIGHT/FOGLIGHT (DIAGNOSTICS)>Diagnostic Procedure with Diagnostic Trouble Code (DTC)>DTC B2911 STEERING RESPONSIVE HEADLIGHT COMMUNICATION LH . |
| U0074 | Ref. to HEADLIGHT/FOGLIGHT (DIAGNOSTICS)>Diagnostic Procedure with Diagnostic Trouble Code (DTC)>DTC U0074 CONTROL MODULE COMMUNICATION BUS "BODY-CAN" OFF . |
| U0101 | Ref. to HEADLIGHT/FOGLIGHT (DIAGNOSTICS)>Diagnostic Procedure with Diagnostic Trouble Code (DTC)>DTC U0101 LOST COMMUNICATION WITH TCM . |
| U0122 | Ref. to HEADLIGHT/FOGLIGHT (DIAGNOSTICS)>Diagnostic Procedure with Diagnostic Trouble Code (DTC)>DTC U0122 LOST COMMUNICATION WITH VEHICLE DYNAMICS CONTROL MODULE . |
| U0402 | Ref. to HEADLIGHT/FOGLIGHT (DIAGNOSTICS)>Diagnostic Procedure with Diagnostic Trouble Code (DTC)>DTC U0402 INVALID DATA RECEIVED FROM TCM . |
| U0416 | Ref. to HEADLIGHT/FOGLIGHT (DIAGNOSTICS)>Diagnostic Procedure with Diagnostic Trouble Code (DTC)>DTC U0416 INVALID DATA RECEIVED FROM VEHICLE DYNAMICS CONTROL MODULE . |
| U1140 | Ref. to HEADLIGHT/FOGLIGHT (DIAGNOSTICS)>Diagnostic Procedure with Diagnostic Trouble Code (DTC)>DTC U1140 LOST COMMUNICATION WITH BODY CONTROL MODULE BODY-CAN . |
| U1422 | Ref. to HEADLIGHT/FOGLIGHT (DIAGNOSTICS)>Diagnostic Procedure with Diagnostic Trouble Code (DTC)>DTC U1422 INVALID DATA RECEIVED FROM BODY CONTROL MODULE BODY-CAN . |
Factory Service Tools
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.