2018-2021 Subaru WRX & STI Headlight Leveling: Module and Sensor Fault Guide

Symptoms of a Failing Headlight Control Module

When the headlight leveling system develops a fault, your vehicle will alert you in several ways. It's important to note that these symptoms can be caused by a failed control module, a faulty rear height sensor, or a wiring issue. Diagnosing the specific cause is key to avoiding unnecessary repairs.

• Headlight Leveling Warning Light: The most common symptom is a warning light on your instrument cluster, often depicted as a headlight icon with up and down arrows. This light indicates a fault has been detected within the auto-leveling system.
• 'SRH OFF' or 'SRH Disabled' Message: On these models, the leveling system is tied to the Steering Responsive Headlights. A fault in the leveling system will often disable the steering-responsive function as well, displaying a message on the multi-function display.
• Headlights Aimed Incorrectly: You may notice your headlights are aimed permanently down, severely limiting nighttime visibility, or aimed too high, causing glare for other drivers.
• No Self-Check at Startup: When you start the car, the headlights should perform a brief "sweep" up and down as a system self-test. If this doesn't happen, it points to a system malfunction.

Common Diagnostic Trouble Codes (DTCs)

A professional scan tool that can read Body Control Module (BCM) codes can pinpoint the issue. Common codes associated with this system include:

• B2900: This code points directly to an internal malfunction within the Headlight Control Module itself.
• B2902: This code indicates an error with the rear vehicle height sensor, which is a very common point of failure.
• U0073 / U0122: These are communication codes, indicating the module is not communicating correctly with other systems in the vehicle.

Diagnosing the Problem: Module vs. Sensor

Before replacing the control module, it is critical to inspect the rear height sensor. This sensor is mounted to the suspension and is exposed to road salt, water, and debris, making it a frequent failure point. Often, the plastic arm connecting the sensor to the control arm can break, or the sensor's internal components can corrode. A visual inspection of the sensor and its wiring harness for damage can often save you from misdiagnosing the problem as a bad control module.

Known Issues, TSBs, and Recalls

While there are no specific recalls for the headlight control module on the 2018-2021 Subaru WRX and WRX STI, owners should be aware of a related Technical Service Bulletin (TSB).

• TSB 07-139-18R: This TSB applies to some 2018 models where the internal plastic of the Steering Responsive Headlight housing could melt from the heat of the bulb. The fix involves replacing the headlight assemblies with a revised design. While this is not a module issue, it is a significant headlight-related problem for this vehicle generation.

Programming and Initialization After Replacement

This is the most critical step after installing a new or used headlight control module. The module does not need to be programmed to your car's VIN, but it must be initialized to learn the new baseline position of the suspension. Failure to perform this procedure will result in the system not working and the warning light remaining on.

You can perform the initialization procedure yourself without any special tools.

1. Ensure the vehicle is on a level surface, tires are properly inflated, and there is no heavy cargo in the trunk.
2. Sit in the driver's seat and make sure the headlight switch is in the 'OFF' position.
3. Turn the ignition switch to the 'ON' position (do not start the engine).
4. Within 20 seconds of turning the ignition on, cycle the headlight switch from 'OFF' to the low beam 'ON' position three times in quick succession.
5. If successful, the headlight leveling warning light on the dash will flash three times and then turn off. You may also see the headlight beams dip down and then return to their original position.

Replacement Information

The Headlight Control Module is located behind the glove box assembly on the passenger side of the dashboard. To access it, the entire glove box and its supporting frame must be removed. While not mechanically complex, it requires careful removal of trim panels and several screws.

• Difficulty: 2 out of 5
• Estimated Time: 0.5 - 1.0 hours
• DIY Feasible: Yes, for those comfortable with removing interior trim panels.

Buying a Used Headlight Control Module

Since new aftermarket modules are not available for this part, a used OEM module is an excellent cost-saving alternative to a new part from the dealer. When purchasing a used module, follow these guidelines:

• Verify the Part Number: Ensure the module is part number 84051VA160. This part is shared between the 2018-2021 WRX and WRX STI models with LED headlights.
• Inspect for Damage: Check the casing for any cracks or signs of physical damage. Ensure the connector pins are straight and free of corrosion.
• Source from a Reputable Seller: Purchase from a seller that offers a warranty and specifies the donor vehicle's year and mileage. Low-mileage parts are always preferable.
• Why Used OEM is a Good Choice: A genuine used Subaru part is guaranteed to have the correct software and hardware for your vehicle. It will fit correctly and respond properly to the initialization procedure, unlike potential aftermarket parts which do not exist for this specific component.

Cost Comparison

The cost savings of choosing a used OEM module are significant.

Frequently Asked Questions (FAQ)