2001 v70 xc - help with brake light switch.

[StoningtonCT]

Hello, I've been sponging info off this site for years but this is my first post after registering.

I just replaced the brake booster and master cylinder on one of the 2001, V70 XC's with 203,000 miles. All is well except the brake light switch. I have adjusted the switch many times and the problem that remains is this. The high center light always work when the brake pedal is depressed. The side brake lights come on less than 20% of the time. Is that indicative of an internal switch failure or something else?

[chrism]

I believe the brake light switch is a single contact that powers all brake light bulbs simultaneously. My guess is that your problem lies somewhere in the rear wiring.

[abscate]

If we can get our hands on a wiring diagram we can confirm this.

[mikealder]

First the diagram which I have colour coded to make it easier to follow in the text below:



Lets start at top right with the fuse 11B/12 this feeds battery voltage to the brake pedal switch, with the pedal switch depressed the 12V travels through the yellow wire going through connector 54/3LG pin 12 before going to the CEM arriving on pin B4. The CEM then inverts this signal prior to feeding out a discrete signal to the REM on the green and yellow wire routing through connector 54/43 pin 13 which is under the left hand side of the rear seat base.

The REM now does two things with the 0V switched signal going in on A4, firstly it provides a +12V output on D4 which is a yellow and red wire this passes through the tailgate connector 54/78 pin 3 where it changes to a yellow wire routing to the center brake light, we know the circuit up to this point is OK because the high level brake light is working. The other thing the REM does is to energise the brake light relay, can you hear/ feel the relays click when you (or a helper) presses the brake pedal)

+12V is fed through fuse 11D/3 which goes to the brake light relay, when this relay is energised it feeds power out on the yellow wires to the trailer socket 54/51 pin 4 and to the Shunt RSH6 which provides bulb failure detection for the brake light circuit, the yellow wire from the center of RSH6 feeds power to fuse 11D/14 (7,5 Amp rated). You should check that RSH6 Shunt is still fully connected to the REM or did it get disturbed when you popped the relays out or changing fuse?

The output of fuse 11D/14 is a green wire feeding power to splice 53/667 which is in the main wiring look under the REM, the splice is a small black heat-shrink covered metal barrel containing three green wires. The two green wires then connect to the brake light bulbs on both sides of the car.

Try fitting a new 7,5A fuse to 11D/14 then see if the brake lights work, if not take the REM off its mounting structure and have a good look at the rear of where the brake light relay is located, check the two yellow wires are still connected to the relay base and not damaged as in burnt out. - Hope this helps (My money is on the brake light relay starting to fail) consider swapping RMI4 (reverse light relay) with RMI5 (outboard brake light relay) and see if the fault moves to the reverse lights, if this is the case replace the relay - Mike

[StoningtonCT]

This is perfect, first thing in the morning I will get back to it.

[NC2001v70]

I do think there is a service bulletin Recall Campaign No.131 on replacing the relay for the rear brake light relay with 2 relays for each light. It may cover your model 2001-2002 v70 and xc70's. I had some rear brake light issues that would come and go like gremlins until I replaced the rear brake relay with the 2 separate ones I hope this helps. The part number for the new replacements was 8651661. You will need 2 to replace in RMI5 and RMI6 positions in the rear REM module.

[abscate]

+1000 to mike alder for thoroughness...

[StoningtonCT]

REM.jpg (305.14 KiB) Viewed 5622 times

Thanks again for the help, I think we have it isolated down to the relay. The car is number 0153xx and that seems to be outside of recall 131 bulletin. Is there consensus on using two relays in the place of the 9494782 for this car?

[mikealder]

Switching to two relays is a better option, the twin position relay was the subject of a recall so Volvo know it was a suspect part - Mike

[firstnamerichard]

I have lost power to all 3 brake lights in my 2001 v70 T5. No bad fuses, bulbs or relays. No power to brake light switch fuse #12 (5A) under the hood. Replaced brake light switch and still no power to fuse #12. What next? Thanks