A4 B7 Curve Light Failure: Repair & Fix

Dear diesel mechanics,

"In my Audi A4 B7, manufactured in 2006, the cornering light is defective, as indicated by the corresponding error message in the FIS (multifunction display). However, the headlights and headlight range adjustment are working perfectly. Also, the self-test during engine start (lights up/down/left/right) runs normally."
It started happening last week when I was refilling the windshield washer fluid and then slammed the hood shut quite forcefully.

I read the following error code using VCDS (control unit 55, headlight range control):

02233 - Headlight module, left (J667)
014 - Defective - Warning light ON.


What has already been tried:
- Error cleared, but reappears immediately.
- Replacing the entire headlight assembly on the left/right side. The issue remains on the left side.
- Sichtprüfung des Steckers am Scheinwerfer. Seems okay.
- Removed the control unit located behind the glove compartment. No error codes were found, but the cornering lights are currently not functioning.

Part number for the headlight power module: 8E0 941 329.
Part number for AFS control unit: 4F0 907 357 E.


What could be the cause here? Is there another "power module" in the engine compartment that is not attached to the headlight?
I have already found a reasonably priced used part for the AFS control unit, but the part number is 4F0 907 357 F. Is this part compatible?

I'm not familiar with the A4, and my knowledge of the Passat 3C, which is of a similar vintage, is limited. It also has two control units in the headlight assembly (AFS + power module).

I believe they are connected via a common bus on the control unit for the lighting system (part number 55). If the "right/left" error doesn't follow the change, then the headlight itself must know that it's supposed to be on the "right" side. If you plug the right headlight into the left socket and leave the actual left headlight disconnected, the system should show an error indicating that the left headlight is missing (or something similar). With your test, you've only proven that there is no wiring fault on the vehicle side.

To differentiate between the left and right sides, only one component on the control unit (STG) might be different, it could be differently coded, or there might be completely different STGs (with different part numbers) installed on the left and right sides. In the case of the Passat, it's the latter, if I recall correctly. Therefore, swapping left and right is not possible.

However, if the engine control unit (ECU) itself indicates a fault, you will likely need to replace it.

PS: You are referring to the part number of a replacement AFS control unit. However, the error memory indicates the power control unit, not the AFS control unit!

Greetings.
Guste.

Thank you for the tip about the shared wiring harness! The control units are the same on the left and right, so I simply swapped them. The problem moved along with it, which makes it clear that the originally left control unit is defective.
Apparently, the side is determined by a bridge located within the headlight housing.

Thank you again!