Brake lights not working 🚨
 

The two side brake lights have been intermittent the past month, on Wednesday coming back from Millport the check brake light message came on the dash and I cannot figure out what's up.... the 3rd brake light works fine, all fuses and wires are good to my knowledge.
What can it be before I take a feed from the 3rd brake light 🤔



The car is a 07 xc90

Hi, I understand that for safety reasons the high level stop lights and the low are on separate circuits for failsafe reasons. If you short them you could start causing further problems.

I also understand that, on some models, part of the stop light circuits are on the cem rather than the rem.

However, on tracing problems on an earlier v70, I discovered my problem was with the relays, in my case the lower port and starboard lights.

I found the problem by swapping relays for those with the same part number.

You need to check the wiring diagrams to see if the relays are on the rem or cem.

My own xc90 is an earlier model so cannot compare.

I hope this helps..

John l

The relays are a part of the cem and not changeable. You can change but need to solder ect.. I'm not getting a signal from the yellow signal wire from the rem but getting a signal when it's going in. I've put a fused bridge on there for the now until I figure out what needs done

Just another thought..

Can you get the part number off the rem?

If you can and then look on the 'bay' you will probably be able to get the same part number unit for < £20. Not sure if it would need programming but I suspect it does not.

Hopefully others could confirm?

Again, I hope this helps.

It needs the brake light input signal for the REM checking on the network with VIDA
Vida will also send that signal manually so checking the REM itself , have you measured the outer brake light feeds from the REM ?

It just needs some simple diagnostics ..

As mentioned by Clan look at the REM relays https://volvos60xc70xc90buyersguide.home.blog/

The yellow signal wire going into the rem is getting a feed but the yellow signal wire coming out has nothing. No fault on the dash when I've bridged the two wires with a 5amp fuse.
I've not had a chance to get visa on it yet but will later this week but my autel points to a short on the circuit so I presume the internal relay is shot?

Well that is a clue .. so you bridged the Green/yellow * (A18) input wire from the CEM to the two Yellow output wires (B3) with the pedal pressed and nothing happens , no voltage ?

There is a direct link through in the REM for these terminals , switching is done in the CEM .

(* = the input signal to the REM from the CEM is a Green wire with a yellow stripe ) .

The yellow wire coming from the cem and the yellow wire from the rem is the ones I've bridged. Never touched a green wire? So if it is a direct link you think just leave the bridge in place?

The diagram I looked at was a 2007 and the one from the CEM is green with a yellow stripe .

Yes the diagram indicates a solid internal REM connection between the two wires .