I just bought a 2008 3.2 to replace my totaled 2005 2.5T. I realized on the way home with the vehicle that the brake and tail lights don't work. Oops.
Observations:
- No brake lights work (including 3rd brake light)
- Tail lights do not come on with the headlights
- Tail/brake bulbs are good
- Turn signals and reverse lights DO work
- Smaller wedge bulbs in the taillight assemblies don't seem to turn on, nor do license plate bulbs (can't confirm any of those are good)
- Fuse #2 in rear fuse box is good
- Fuse #9 in fuse box under steering wheel is good
- Disconnecting battery for 20 minutes had no affect
- I get a position bulb warning (probably unrelated as one of the front ones seems to be out)
- I CAN put the truck in gear from park while running without pressing the brake pedal
- I get a gear selector service warning

That last bit makes me wonder if someone disconnected the gear selector lockout to drive the vehicle, because the brake light switch or something may be bad, which was locking in Park? That's a crazy "fix" but I've seen worse.
However, I don't understand why the tail lights wouldn't work. I've found diagrams describing the brake circuits but they don't also include anything about their function as tail lights.

 

OK, some red herrings. Those small wedge bulbs are in fact the tail lights, the brake lights are just brake lights. I replaced those bulbs, so now the tail lights work. I also replaced the license plate bulbs, and those work. My rear fog/marker lights are just dummy reflectors in this one, not sure why they have wires running that direction from the taillights but that cavity is empty and the bulb hole is plugged.

I disconnected the brake light switch, and the brake lights didn't come on. I even put a new switch in it, but no brake lights still.

So: No brake lights (neither side nor center) function. Brake light switch is good, brake light switch fuse in CEM is good. Gear selector lockout not working (probably disconnected, not sure where to look for that however).

What's left? CEM? Pretty annoyed at this point, not gonna lie.

 

A wiring diagram can be found at volvodiag.com

Do you have 12v (with your $8 test light) on the red wire at the brake light switch? Or on the Yellow wire going to the tail lamp assembly?

 

I do not have 12V at the switch. I didn't specifically test the yellow wire.

Edit: Hmm, but I DO have 12V at fuse 9. And the fuse is good, I checked that yesterday. So, either I screwed up measuring from the switch connector or I have a bad wire??

Shouldn't any of this cause an error code? I don't get any warnings about brakes on the dash display.

 

On some Volvos if all the brake lights are out you don't get a bulb failure warning. A good next step would be to scan the car with a compatible scanner that can talk to all the control units. Below is a screen shot from Vida - showing how you can activate the brake lights with the scan tool.

 

My current OBD2 reader sadly does not support all of this. I want to get Vida going but still figuring that out. In the meantime, I have an appointment at an independent Volvo specialist for tomorrow, in case I can't figure it out today.

 

Crap. I'm just sitting here thinking about this problem, and realized if the issue were not getting 12V at the switch, the brake lights would be stuck on, not off. So I probably measured the wrong contacts on that connector, given that there is 12V at the fuse.

 

no, the switch sends 12v (eventually) to the bulbs - so is there 12v on the red wire at the switch? and the other wire (y-r) when the pedal is pushed?

 

I think the switch is open when the brake pedal is pushed? The 12V loops around to an input on the CEM so breaking the signal should cause the lights to come on. At least, that's the way I read the diagram, and it squares with what I've observed.

 

The diagram shows the switch open - or the wire leaving it would be red. And I've never seen a (Volvo) brake light switch that opens when released - they always close when released to send power to the bulbs.

 

I ended up giving up and taking it to a shop. The problem was one or more broken wires in the wiring harness connected to the CEM. Got that fixed and now it's working as expected.

I still have no gear selector (from park, no need to press the brake pedal) and a Gear Selector Service Required warning. I can't manually shift either, not that I ever would in this thing. Other than that it drives perfectly.

 

...and now the gearshift errors are gone. There was no fuse at all in slot 21, for the TCM. Put one in there and voila, all gearshift problems have vanished. I'm guessing that was someone's solution to getting out of park with the brake sensor circuit issue.