I've been struggling with this issue for some time (posted back in April, but I have more information now), and I'd appreciate any help anyone can offer. Occasionally, like once every few months, everything on the high-speed CAN bus fails to communicate for a while. If it happens while the car is stopped, it won't crank. Using the iCarSoft tool, it says it cannot communicate with the ECM, CEM (high speed side), BCM, and TCM. If it happens while the car is running, all the gauges go dead, AC and cruise don't work, but the car will drive until you turn it off. Same deal with the iCarSoft tool -- it can't talk to the high-speed CAN bus stuff, doesn't even detect it is there. Then, if I let it sit a few hours or days, it would work like normal after that. The modules reported "communication failure" trouble codes, and sometimes random other codes that don't seem to be actual problems, like brake pedal sensor or immobilizer antenna (replaced both of those, no effect). I took it to several dealers but somehow the problem had always gone away by the time they got to it. I replaced the BCM and had the ECM and TCM checked by Xemodex, who said they were fine. I had the CEM upgraded by Xemodex to their heat-resistant version (I live in Alabama), but they said they could find nothing wrong with it. One thing that has worked recently to get it going when this happens is to either jiggle the ECM (in the box beside the power steering reservoir) or remove and re-seat the ECM with the special Volvo tool. Then it will generally start, again just reporting communication failures if you read trouble codes from the modules. My current hypothesis is that the socket for the ECM is the culprit. This seems very difficult to replace given that the wiring goes everywhere from that socket. Any ideas on how to improve the socket-module connection? Or any other suggestions for a diagnosis that matches these symptoms? Thanks!