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Rear fog lamps not working

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I have 2012 CTS4 Sport Wagon (export model). Rear fog lights stopped to work after car battery was failed (worked fine before that). I can see via Tech2 (BCM ext. module) that there is a switch and lights for rear fogs, but I cannot turn those on from Tech2 nor the real switch. No error codes found from BCM. Fuse (in rear compartment box number 18) is ok. Any ideas where to start to solve this issue?


Marko from Finland
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I checked every fuse what I found from the car (front and back) and all are ok. I also opened and closed all of the connectors near battery. Then I connected Tech2. This time I was standing in back of the car and noticed that when I set lights on (or off) via tech2 I hear a relay click sound, so something is happening but still no lights. That relay sound comes from the drivers side (opposite to battery which is located in passenger side). This is all what I have now tested without any need to open any extra panels. Next step could be panel removal and check that wiring is ok (which should be..).

First thing what I suspected after I noticed this issue was this "system reset" back to US configuration while car was out of power. But that information is stored in to BCM code and it should never lose that information. If I have understood correctly this rear fog option is only in export models (+ Canada)?. Can someone check via tech2 or similar if you can see rear fogs from the BCM aux module? Only way to be sure that I have correct options selected in BCM etc systems is to re-flash all modules (didn't see any enable disable options in tech2 tool)?

- Marko
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Hi All!

Here is an update for this issue. It took some time to get this problem solved. First, I hooked up MDI in to the car and re-flashed software to BCM. That did not help. Next I acquired wiring diagrams and checked all the cables and connections which were ok. Next I tested the relay in the rear compartment (which controls the fogs) and it worked fine. Last thing was to get new multifunction switch. After I changed that I got the rear fogs back to work again.

Hope this resolution helps someone else who has the same problem to fix the issue :)


Marko from Finland
Yes. I'm referring to that very same turn signal arm. I assumed that it is located in the same place in USA models too, that's why I said just multifunction switch.
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