2004 V70 2.4 baffiing canbus issue after "sleep" timeout

[krhodes1]

I gave my Mom my '04 V70 (base 2.4 automatic) after Hurricane Ian drowned her car. Hoped to get her by until the new car market is a tad less insane. Haha, Volvos do NOT like my mother... I get the dreaded phone call, again, "there is something wrong with the car". Go over to have a look, find that everything on the low-speed canbus is dead. Car starts and runs fine, but no lights, A/C, windows, trans in limp mode, nothing on the dash but the CEL, etc. Pulling the fuse for the CEM and reseating it puts all back to normal, SRS message and CEL clear with VIDA. Codes are all "no communication" to this and that as expected. Car is fine for a couple weeks, does it again. Send the CEM out to Xemodex for testing and a "rebuild" if needed, sure enough they come back saying it's the usual overheating problem. Get the CEM back, plug it all back in, car starts right up and seems fine.

Now to add spice, Mom has bought a new car, and I have sold the Volvo. I need to deliver it to it's new owner in MA - I live in FL. So thinking everything is fine, I jump in the car and head north. Get to my first stop, Jacksonville, 400 miles away, and get gas, go to the bathroom and grab some snacks. Car starts, runs for a few seconds, and stalls. Oh crap. Cranks, doesn't start, dash is dead, all the same symptoms (other than the no start, that's new and exciting). Except I happen to turn the key back to off, then try to start it again - and it starts right up and everything is fine. Only remaining symptom, the SRS warning message. No CEL this time. What I figured out over the 1700 mile trek to New England is that it will ONLY do this if the car is off for more than about five minutes. Less than five minutes, will restart and everything is fine. More than that, and you have to do the key to on, back to off dance, then it will start and run and everything works just fine. And to be clear - it's turning the key back to OFF that seems to wake it up. At that point, everything works that should work with the key off. Central locking, lights, etc. Since it was working now that I knew the trick, I did not touch ANYTHING until I got home to New England. Instead of leaving the car with the buyer in MA, I head for my summer place in ME where I can work on it and get it sorted out, he's happy to come get it once sorted out. I did have a nice lunch with him along the way so he could see the car at least.

So I think "Xemodex must have not gotten things quite right". Contacted them, described what is going on, and they said "send it back". Which I did. Today, they let me know that on their test bench they could not find any issues! They are still transferring my software to another rebuilt one and sending it back though.

I feel like the answer has to be in the fact that it is fine until that timeout period passes. Does the CEM control that, or does some other module? What is supposed to stay awake? Obviously, at a minimum the central locking has to be listening for the remote. When it goes dead, that does too. Again, within the about 5 minute window, everything works just fine - you can get out of the car, lock it with the remote, unlock it, get in, starts first turn of the key, etc. After that - nothing until the two-step key dance. Leaving it unlocked makes no difference. The big difference compared to before is that the fuel pump is not getting turned on when it's dead - that was NOT an issue originally - the car would start and run fine -.In fact, the first time it happened, Mom was out running errands and she drove it home like that.

Is this controlled by one of the relays on the CEM? How does that timeout actually work? I am pretty sure I put the relays back the way they were, but I have done dumber things than that with cars.

Hopefully one of the folk here knowledgeable in the mysteries of the Volvo electrical system can point me in the right direction. I won't be back in ME to deal with it for another week and a half, so I have some time to make a plan of attack. Thankfully the buyer REALLY wants the car and is not in a hurry. Completely rust-free never-seen-salt FL car in very, very nice condition other than this!

Kevin Rhodes
'04 V70 (slightly possessed by demons)

[jonesg]

videos on youtube show how to track this down.
I think it was on pine hollow channel.
where in Maine ?

[vtl]

Post all errors read out with VIDA, even inactive ones, once it freaks out again.