Hello, i have this 2005 2.5T XC90, and i have one hell of a problem, well for me it is.

Driving it yesterday, all of a sudden it showed brake failure stop safely, the ABS light lit, check engine, oil logo lit as well, odometer going all to dashes ---- and then, the RPM and speed gauge not working. The car still worked, but in kind of a limp mode where it felt with no kick. It was raining here yesterday and there was a lot of watter 'puddles' ? im french.. in the street, so lots of water going under the xc90.

Anyhow, i came here and searched online, some references to the CEM, some to the TCM, DCM or DEM.. But i couldn't find a clear answer, i still don't know what happened. My xc90 had the redesigned plenum installed 2 years ago all sealed with sillicon, and the CEM cleaned, connectors greased, corrosion cleaned and everything. I checked, no water came in there yesterday. it's all dry.

What i did yesterday night, is to remove the car's negative side of the battery. Somehow, after resting for the night, all started OK this morning. Did something dry up ? IDK. But what i know, is that i have another problem now, the 3 back brake lights are always on. Each sides, and the middle one, all lit.

I tought after a bit of research it could be the REM, which seems to control the back lights. So i pulled that off, tested the relays with a small 12VDC power supply, BAD IDEA. I burned some small SMD diodes, which i just ordered from digikey, lucky enough that i have some microscope here, and i hope it didn't fry much more on it. I'm in a middle in a nightmare, well for me it is.

So the car is pretty much undrivable because no brake lights right now, and it's my wife's daily driver. I ordered a Dice from china right away to be able to find out a bit more about the problem, found some wiring diagrams.. Hell, i got not much time to figure that one out, but i need to !!!

Any help or input would be really appreciated, i can pay if someone can give me a few tips even to walk me through this. I'll fix the REM hope i didn't break more stuff tomorrow, but still need to find out that 3 brake lights issue, and what the hell happened with the xc90 yesterday. thanks !!!

 

Um, i just replaced the 2 burned out smt diodes on the board (that i burned myself with incorrect testing), and put everything back in place.. everything works now, i don't get it. i hope vida with dice will shed some light on the actual issue that happened, because now everything seems to work fine. I have a bad feeling issue is just intermittent and not fixed now, so i still need to figure out what happened.

 

volvo cem module in under the dash and can typically get issues with solderings going bad. it can cause the symptoms you had. other possibility is the instrument panel going bad - again same symptoms, but it shouldn't affect engine performance. google "volvo cem xemodex"