Hi all,
I have a 2004 XC70 that I have spent the last two years trying to diagnose, after having a couple of dealers claim they can't find the problem. Symptoms: every once in a while most dashboard gauges, lights, and the shift indicator stop working. The cruise control and AC don't work either. The car will run and drive (sometimes with a message "reduced engine performance") until you turn it off, but then it will not start for a while. After just sitting a few hours or days the car will start and run normally, sometimes with "check engine lit", sometimes with "Transmission Service Required", sometimes with "Brake failure stop safely". I got the iCarSoft Volvo diagnostic unit and have consistently checked the codes when this problem happens. I always find for the CEM, ECM, TCM. and BCM the trouble code "communications failiure". Sometimes there are other random codes such as "Brake pedal position sensor" or "immobilizer". I replaced the pedal sensor and immobilizer antenna but it didn't help. I have had the ECM, TCM, and BCM all checked by Xemodex, and they found no problem. On the off-chance it was heat related I had the CEM upgraded to their heat-tolerant version in spite of it checking out fine. That didn't fix it either. If you connect the diagnostic tool while the problem is happening, it can't communicate with any of the high-speed CAN bus modules -- it doesn't detect them if you let the tool auto-configure, and it says it can't communicate with them if you manually select a model and year. It finds all the low-speed CAN bus stuff just fine, all the other modules. The one thing that I have found that helps is jiggling the ECM in its socket, or worst-case removing the ECM and re-seating it with the special Volvo tool for doing that. My bet is that the connection between the ECM and its socket is iffy, particularly the socket is the iffy part. Given that that socket and wiring harness appears to be near-impossible to replace because it has a million wires that seem to go everywhere, does anyone have any suggestions how to improve the contact between the ECM and its socket, or another diagnosis consistent with all this info? Thanks! I love this car, but I am getting very weary of repeatedly temporarily fixing this. I already don't trust the car on anything longer than a cross-town trip.