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Discussion Starter · #1 ·
The DMV recently discovered a brake light issue with my 2008 Volvo s40, which needs to be fixed somewhat quickly. This is the first time that I've had to do any real investigation into electrical issues on a Volvo, but I've faced similar things with Volkswagens in the past, and I'm pretty sure that there will be a relatively simple, inexpensive fix, but that dealerships and repair shops will usually present you with the most expensive option. So, hopefully someone here could point me in the right direction, or at least help me go into a repair shop with some degree of knowledge.

The issue is this: although the top brake light situated on the rear window is working properly, the lower brake lights (both right and left) in the tail light housings are not. When I hit the brake, the lower brake lights flash for a split second and then go out, even if my foot is still on the brake. The bulbs are fine, and the fuse below the glove compartment that corresponds to brake lights (according to the driver's manual) is fine. One repair shop took a look but said that there was likely some sort of problem surrounding the CEM but the shop was unable to do anything because they don't have the correct software to fully diagnose the situation. The shop was able read some faulty codes related to lower brake light signals (8D05, 8D06, 8D07, 8D08) and two others (DDOA and DDOC, I believe); they also said the lower brake lights were getting voltage in a resting state when they shouldn't be, and then that there is a brief spike when the brake is pressed. However, they could do nothing more than read those codes.

I have read things elsewhere suggesting that a faulty relay may be the culprit, and it sounds like this would be an inexpensive fix. However, I have not found anything directly on point to a 2008 s40, and I don't know where the CEM or potentially faulty relay is actually located.

Any guidance would be greatly appreciated!
 

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I would search out the wiring diagram for your car. It will show the corcuits down to the relay level. I've seen headlight relay problems fixed by relay replacement.
 

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Check the grounds at the tail lights. I had a bad ground on my left rear cluster give me the bulb failure light all the time... annoying.
 

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Discussion Starter · #5 ·
Thank you all for the help. I haven't been able to do anything about the problem myself, but the car is in the shop and at least I can be prepared for whatever they throw my way. Fingers crossed.
 
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