Check Stop Lamp message

idainc30 · Post by **idainc30** » 11 Jan 2023, 07:19

Only one of three brake lights is out. Changed bulb which was OK and problems still continues. Checked fuses and all are OK. I've read any number of posts that refer to the relay (s) in the rear but my local mechanic says that would affect all three brake lights and not just one. He is suggesting the socket itself as the wiring schematic has all three on the same circuit.

Would much appreciate and and all ideas.

Post by **ggleavitt** » 11 Jan 2023, 08:36

: XC90 Brake Light Schematic.JPG (55.92 KiB) Viewed 2515 times

idainc30 · Post by **idainc30** » 11 Jan 2023, 10:53

Thank You ! But I'm a mechanical engineer not electrical. Can you interpret this for me ? Thanks !

Post by **ggleavitt** » 12 Jan 2023, 11:51

REM terminal F4 (white wire) provides power to the center high stop lamp.
REM terminal B3 (yellow wire) provides power to both lower stop lamps.
You also have a ground (solid black wire) common to the lower lamp assemblies, this is somewhere in the back of the vehicle under the cosmetic cover and might be between battery and tailgate. Not necessary to check if you have ANY other lights working as the ground wire is common to the entire light assembly.

That you have one lower stop lamp working properly and one not working would intuitively suggest an electrical connection issue and not an REM fault. At least to me it would...

idainc30 · Post by **idainc30** » 12 Jan 2023, 16:24

Thanks. I agree as does my mechanic. I may get a new tail light wiring harness for about $75 or so. It seems to be the likely culprit. Or maybe a shot of WD40 or a contact cleaner although they did look pretty good.

It appears I have to replace the entire harness...

Much appreciate the help 1

Post by **ggleavitt** » 15 Jan 2023, 08:34

My apologies, having seen your post on Swedespeed and recognizing your signature (MY04), I provided an image of an incorrect wiring diagram. There are indeed some wiring and module changes that occur after MY05, my diagram what either 05 or 07. The MY04 wiring diagram on Swedespeed notes the same common connection between left and right light assemblies so I still believe that your issue is wiring and/or socket but I did want to point out the data error in my response. I won't repost that version EWD as it's already on the other thread you created.

idainc30 · Post by **idainc30** » 16 Jan 2023, 07:20

ggleavitt wrote: 15 Jan 2023, 08:34 My apologies, having seen your post on Swedespeed and recognizing your signature (MY04), I provided an image of an incorrect wiring diagram. There are indeed some wiring and module changes that occur after MY05, my diagram what either 05 or 07. The MY04 wiring diagram on Swedespeed notes the same common connection between left and right light assemblies so I still believe that your issue is wiring and/or socket but I did want to point out the data error in my response. I won't repost that version EWD as it's already on the other thread you created.

Thank you for posting this. I sprayed the brake socket with cleaner and ensured there was good contact with three good bulbs and none lit up. Ordering a new harness which apparently is available with and without a fog light which quick connects to the harness.

idainc30 · Post by **idainc30** » 24 Jan 2023, 12:55

I replaced the tail light harness with a new one and a new bulb and the condition still exists. Drivers side brake light still out. Any ideas ? In a quiet garage I can hear the relay go on and off when I step on the brake.

idainc30 · Post by **idainc30** » 08 Feb 2023, 11:06

Solved. $166 for my mechanic to track down a bad ground 31/72. No more message on dash. Add another $85 for the new harness.