2004 XC90 NO brake lights

Leesplus14 · Post by **Leesplus14** » 19 Feb 2022, 16:52

Good evening everyone. I just purchased an 04 XC90 with 168k miles. Recently replaced battery before we purchased it, has no brake lights at all. We have replaced the relay, third brake light, all bulbs are good, all fuses are good. Any other ideas?

Post by **Krons** » 19 Feb 2022, 16:59

I'd chase the voltage...any power at the relay? Possible replacement relay is bad.

Post by **Krons** » 19 Feb 2022, 17:02

Worth reading this:
viewtopic.php?t=99455

Leesplus14 · Post by **Leesplus14** » 19 Feb 2022, 17:04

Krons wrote: ↑19 Feb 2022, 16:59 I'd chase the voltage...any power at the relay? Possible replacement relay is bad.

We have power at the relay and have replaced the relay with two separate new relays, still nothing. Brake switch has been replaced as well.

MARCUSBUTZIN · Post by **MARCUSBUTZIN** » 16 Apr 2022, 18:37

2011 XC90 I have third brake light (upper center ) working but not either side. Is the relay on the left corner interior? Does anyone know if there is a brake light relay under the hood? Advise please!

Post by **ggleavitt** » 21 Apr 2022, 08:57

See the attached. Center brake light (10/19) is powered via REM and it's an LED light bar of sorts with a transistor on the input for switching. F2 is the fuse on the REM, manages more than just this light (see owners manual https://volvo.custhelp.com/app/manuals/ ... model/XC90 for detail).

The REM is in the left rear of the cargo compartment, you'll need to remove the rear corner floor triangle shaped insert and pull the fascia panel to see it.

: Brake Lights XC90_2010.JPG (51.3 KiB) Viewed 1162 times

chitownV · Post by **chitownV** » 21 Apr 2022, 15:14

Leesplus14 wrote: ↑19 Feb 2022, 17:04
Krons wrote: ↑19 Feb 2022, 16:59 I'd chase the voltage...any power at the relay? Possible replacement relay is bad.
We have power at the relay and have replaced the relay with two separate new relays, still nothing. Brake switch has been replaced as well.

Wonder if the original poster got this diagnosed or resolved seeing it’s all brake lights.

Do the parking lights work or are they also out? What about reverse lights?

MARCUSBUTZIN · Post by **MARCUSBUTZIN** » 21 Apr 2022, 15:54

Krons wrote: ↑19 Feb 2022, 16:59 I'd chase the voltage...any power at the relay? Possible replacement relay is bad.

Location of the relay please, I have a 2011 with only the center section up working (3 rd brake light ) is the relay under the hood? I looked at the small circuit board in the left rear corner ( the baggage area, trunk if you will ).

Post by **ggleavitt** » 21 Apr 2022, 17:24

My bad, got it reversed, the center light works but not sides. The block assembly in the left rear corner is your Rear Electronics Module (REM) as noted in the drawing above.

You'll want what's likely the Field Effect Transistor (FET) responsible for triggering voltage to REM B:3 in the diagram above. I won't have a component layout for the REM that gets to a component level and I'm not sure who else will.

Why not try to see if you get voltage on fuse 30 in the REM block. If you do then trace from the light socket center pins to the REM pin B:3 with an ohmmeter and a dead vehicle all the way to the light sockets, see if it's wiring. I understand the relay thing but there have not been wholesale relays on these modules since MY05 as I am aware (original poster had a MY04).

I might keep the troubleshooting basic for a start, see how far you get with voltage and fuse/wiring continuity. No way to read your vehicle with something that understands Volvo codes?

Post by **ggleavitt** » 21 Apr 2022, 18:20

Going to add to this, it's maybe not so simple as I described earlier now that I've had a closer look at VIDA (and the drawing that I posted). The Central Electronic Module (CEM) controls the side lights via the brake switch and passes 12V directly to the REM where the output to the side brake lights occurs. It's the Green/Yellow (GN-Y) single wire that connects from A:15 on the CEM to A:18 on the REM in the drawing.

I would still do basic troubleshooting of the brake switch, the REM fuse, and the Solid Yellow (Y) conductor wire path from the REM to the lights themselves but if your issue is the CEM not triggering the REM or an internal REM thing, you'll need to get something connected to your vehicle to really troubleshoot it.