It all started when my wife was going to run errands. She started our ‘07 XC-90 3.2L and immediately came and got me. ABS, anti-skid, brake, and the red triangle of doom were all lit along with the “Brake failure stop safely” message. I’ve never had this message appear before, so my first thought was that it lost fluid or something. I couldn’t see anything physically wrong, the pedal had good feel and it stopped ok in the driveway, so I took it for a test drive. I didn’t do a panic stop to see if the ABS would activate but the brakes were fine. I did discover that the trip meter was not displaying, the odometer froze, the cruise control was inoperative, no avg speed, gas mileage etc. You can drive the car in this condition but outside of getting it home or to a garage you shouldn’t. The transmission was having difficulty engaging smoothly, and I got two more messages, “Engine system service required,” and “Engine system service urgent.” Seemingly unrelated, the heated seats also stopped working.
A scan revealed the following codes,
ECM
U012200 - lost communication with BCM
P050087 - vehicle speed sensor A bus signal/ message failure
C004082 - brake pedal switch A bus signal message failure
CEM
1A5F - communication with BCM signal missing
TCM
P179900 - CAN TCM ABS circuit malfunction
CCM
DD12 - LH seat heater no communication
DD30 - RH seat heater no communication
At first glance it appears that the BCM ( Brake Control Module) is the bad guy. Following VIDA’s fault tracing, I checked all the connectors (BCM,ECM,CEM) no corrosion or obvious damage. I don’t have a breakout box but I was able to establish that the power and ground wires to the BCM were good. I threw a junkyard BCM in it just to see if anything would change but nothing did. At this point I thought either I had a dead BCM or an open or shorted wire. So I wandered into the dark Forrest that is the XC90 wiring diagrams, and discovered that the heated seat fuses were directly above the BCM fuse on the CEM’s fuse block. The fuses were good, but there was no power going through them. I jumped power from another 5A circuit to the BCM fuse and all the warning lights went off and the brake failure message went away. I removed the CEM and opened it up expecting to find some crusty circuits but everything inside looked shiny and new. However when I traced the circuits from the BCM and heated seat fuses they both terminated at the same relay. There are two Tyco V23134-00J52-X455 relays. I retrieved my multi meter and HarborFreight jumper box and tested the relay. The resistance across the control coil should be 75-90ohms. The suspect relay was 0.4ohm. Just for the halibut I put power to it with the booster and got nothing. Tyco no longer produces this relay but there is a ‘discontinued replacement’ available. I forget the manufacturer but they were priced at $10.00US and you had to buy a minimum of 5 at the site where I found them. I decided to go cheap and went to the junkyard and pulled a CEM for $22.00. I learned that the solder they use to mount these has a very high melting point so I had to use a butane torch to swap them out. You have to be careful not to overheat your circuit board! I used a high quality silver solder to install the relay. So far no issues. If I ever do this again I’ll check with some local electronic repair shops to see if they can properly and neatly install the new relay. In VIDA’s possible causes lists in the codes, only the ECM U012100 mentions an internal fault in “another module” as a possible cause.None of the DTCs call out the CEM specifically. So if you get the brake failure message and at the same time you lose your heated seats, most likely a $10 relay brought your Volvo to its knees. Before you ship your modules off for rebuilding for hundreds of dollars if you are reasonably handy you can fix it for less than a hundred bucks

 

Wow, that is some quality troubleshooting. Impressive.

 

Thanks! The most important part of it was looking at the wiring diagrams and discovering the BCM fuse directly below the heated seat fuses. I thought for sure I was going to find some crusty corroded connections in there. I’m thankful I’m blessed with a little bit of mechanical inclination. I’m sure if I took it to a garage I’d be shelling out a pile of money for a new module. Or three. 😁

 

Brake failure is a bad thing.

 

I'm having the same problem all my lights came on in the same order. Hardly no power to make it back home, the key light even came on and key wouldn't come out it took a few times. Can you help me with this please? My husband has a code scanner

 

JUST CHECKING IN. It is now January 2026 and i have had no issues with the CEM.