XC 7O brake failure/abs/loss of cluster/limp mode

Nick3501 · Post by **Nick3501** » 10 Feb 2019, 18:59

I've done some searching and I've read about the same problem from Volvos over many decades but I can't really narrow down what I should be looking at.

basically my gauges go dead and I get a brake failure warning and if this happens while I'm driving I also get a nice thump from my transmission presumably going into limp mode. I know this is a problem with one of the electronic modules taking down the rest of them due to bad connection at least that's what my research suggests. problem is is I don't know which one it is and I don't even know where they're located. are any of them known to be problematic if so which ones and where are they. obviously I'm going to try cleaning and looking for a corrosion water ingress etc.

this is been going on for a couple months but recently the car will start and then die a couple times and then it will refuse to start at all and it smells very rich as if it's flooding itself out. any tips are greatly appreciated.

Post by **abscate** » 10 Feb 2019, 19:13

You've got multiple issues, so you will need VIDA to reset bricked modules and start your troubleshooting.

On a CANBUS car, one module failure can interfere with other things but you can't diagnose by symptom or traditional troubleshooting

Nick3501 · Post by **Nick3501** » 10 Feb 2019, 19:15

I read about 04 having a CEM issue with heat.

Nick3501 · Post by **Nick3501** » 10 Feb 2019, 20:18

so things I've noticed that might differ. my transmission is in limp mode because it shifts very harsh into reverse and drive I believe that's a Fail-Safe sort of high pressure thing. the little lights beside my shifter that change from park to reverse neutral drive etc don't moveit always stays in park also on the dash it always says it's in park even when it's in drive or reverse or whatever. sometimes the car doesn't want to start it just cranks but doesn't start. I get brake failure message transmission service required message engine service required message. when I restart the car I can get maybe 10 or 15 seconds of all my gauges working until they all fall to zero and all the errors come back.

Free2drive! · Post by **Free2drive!** » 11 Feb 2019, 03:01

I know your issues, I've got an 04 v70. I'm on my third CEM. I spent hundreds on reading codes. Nothing definite was ever diagnosed and I was often left unable to drive car away from garage.
It has been completely random, hot weather cold weather long trip short trip, we never solved it.

But it hasn't done it for months now, and is running fine.

See if Vida highlights anything
Check battery
Check alternator is charging
Clean all grounds
Clean contact on TCM module and ECM module
Check CEM for water damage and/or burning.

Keep posting on this site as the information, advice and encouragement stopped me going mad.

Matt

Nick3501 · Post by **Nick3501** » 11 Feb 2019, 11:22

thanks for the info. battery is new and charged in fact I left the key on for probably five minutes with the headlights on today and it still started the car so I think the batteries okay. voltage is about 14.

just so I have this right the TCM and ECM are under the hood in a plastic box right? and the cem is under the dash behind the fuse panel on the driver side?

Nick3501 · Post by **Nick3501** » 11 Feb 2019, 12:43

the only specific code set was P0571 cruise/brake switch circuit. the rest were U codes dealing with serial communication link problems

Post by **precopster** » 11 Feb 2019, 15:52

Looks more like CEM than any other module. In my experience after swapping out about 6 of these there will be no physical evidence on the CEM of failure.

You can send the CEM to XeModex for checking. Look on their website for removal instructions.

Nick3501 · Post by **Nick3501** » 11 Feb 2019, 15:57

yeah i took apart and everything looks good. no burns no obvious bad solder. no moisture evidence. The error went away for 10 minutes and came back. Now the car wont start and the only code is U0002 network/communication

Nick3501 · Post by **Nick3501** » 11 Feb 2019, 20:24

after a few hours of research on this site and swedespeed and Volvo XC. Com... on a whim I climbed under and disconnected the DEM on the differential. to my surprise it started right up and all are codes were gone. obviously I have to wait and see if the problems going to come back so I don't know if this was the cause or not.

I read a few instances of the d e m bringing down the whole canbus network and causing very similar problems and one user in particular said that pulling the fuse did not fix the problem but physically disconnecting the harness did. only time will tell I got to put it all back together now.