I had a random issue where my central electronics module (CEM) would lock up, resulting in nothing on the low-speed canbus working. No instrument panel other than check engine light, no sunroof, windows, central locking, A/C, trans stuck in limp mode, etc. But it would start and run fine, other than limp mode meaning only 3rd and reverse. Pulling the CEM fuse would reset it and it would be fine until it did it again.

Sent it off to Xemodex to be rebuilt. Got it back, put it back in being (I thought) careful to get all the relays and shunts back in the same place (I took pictures) and now I have a VERY consistent new problem. If the car sits long enough for it to "slleep" (not sure of the exact amount of time 5-10 mins), the low speed bus will be dead again. No central locking is the first obvious symptom, and it will crank but not start (that is different than before). Same symptoms as before when the key is turned to position II - panel dead but for the CEL, no windows, sunroof, A/C, etc. BUT all I have to do is turn the key back to off, then position II again and it will light up everything and then start right up. If I shut the car off and restart before the timeout for it going to sleep, it's fine, no issue. 100% consistent behavior except the very first time after I put the CEM back in - then it just started right up. I was up against a deadline for a trip so thinking it was fine I jumped in the car and headed from Florida to New England (I'm stupid like that). Imagine my surprise when it did the above at the first gas stop. But it has been 100% consistent, and along the way I figured out the sleep aspect. For example, if I JUST stop for gas, no problem, everything is fine when I get back in. If I get lunch, that is long enough for it to go dead. Dead every morning. Come back to the car and no remote unlock, and two key twists to wake it up. But other than the clock now being wrong and the initial time setting an SRS message (the original issue did that too - I can clear it with VIDA/DICE), it;s like nothing is amiss.

Since I didn't want to strand myself somewhere, I have not touched *anything*, as I am not quite at my destination yet. But I figure at a minimum I am going to pull the CEM back down and make sure all the relays are well-seated, maybe swap around a couple that seem relevant to the issue. Unfortunately, tomorrow is a holiday in Canada so I can't call Xemodex and see what they think. I also brought my VIDA setup with me so I will scan for codes, though I don't expect I will see anything but bus communication errors, just like before.

The Xemodex trouble report just said that the CEM had heat-related issues. I did not see any obvious issues like corrosion or burned contacts. So maybe chicken and egg problem? What ever is causing this was causing the faulty CEM to lock up, but now that it's "fixed" it no longer locks up and the real problem is now evident?

Anyone have any ideas or seen this before? Does the CEM control that timeout when everything geos to sleep? And does anyone have a good copy of the CEM relay chart? I have VIDA with me, but not the electrical diagrams it references, and the only one I found online is not very legible.

Many thanks!

Kevin Rhodes
'04 V70 2.4 141K

 

A bit of an update - discovered that it WILL actually start with the first turn of the key, but the fuel pump isn't turning on so it only runs for about 5 seconds and stalls. Then won't restart until the key is turn back to off, at which point everything lights up and it is all good until it sits long enough to go to "sleep" again. Super wierd. But it made the 1700 miles to Maine with no problems. Will be calling Xemodex tomorrow, sure seems like the rebuilt CEM has issues. Has to happen once in a while.

-Kevin Rhodes

 

don't know if you still need your wire diagrams, but heres a link, you can download them once the pdf loads in your browser.
or you can pay $2 there for a copy loadable into VIDA, though i cant speak to the efficacy of that
https://volvodiag.com/ewd-online-eng/

 

Thanks for the reply! It was the CEM - Xemodex rebuilt it again and all was well. Car is now on to its new keeper.

Kevin