CEM fault
 

Can anybody help with this, please?
I have a year 2007 C30. She has an annoying & intermittent fault with the instrument cluster.
First thing: The engine management warning light is on. My garage says that it is an EGR valve fault. But they also said that my car does not have an EGR valve.
Second thing: Occasionally all the instruments & warning lights go out. And stay out until I turn the engine off & back on.
One garage has failed to fix the problem, & two others have decided not to help. Apparently the CEM module is suspect, & replacements are hard to find.
Has anybody else had this?
Are CEM unit repairs a viable option?
Are secondhand units worth looking at?
Any help or advice will be appreciated.
Many thanks,
Andrew

This is a case where the dealers are the only experts that have been dealing with this kind of problem for 15 years now . So know what to do.
There are 3 pairs of network terminals in 3 different plugs in the cem , volvo do a repair wire with a terminal attached ( x 6 ) . That is the first thing to get done cleaning doesn't do much long term , The new terminals have a stronger grip.

The CEM is known for connection problems. You can sometimes clear the faults by cleaning the terminals, but this is often only a short term fix (if it fixes it at all).

It's worth removing the smaller rectangular connectors (blue,green,brown) on the CEM and checking inside for any signs of water ingress, or corrosion (white or green powdery deposits),

Clan is correct that the long term fix for communication issues is replacing the connector terminals. It's a fiddly job in an awkward position, but it's not much more complicated than soldering two wires together (for each of the 6 terminals that need to be replaced).

CEMs can fail, but the replacement needs to be programmed to your car, or the immobiliser will not allow the engine to start (among other things). This can be done with a brand new CEM by a volvo dealer, or your original CEM can be cloned into a second hand unit.

Most garages are useless when faced with this fault on these cars, as they only go on what their fault code reader says, and communication errors will trigger random unconnected faults to be stored, so it's not uncommon to hear of cars with many parts replaced and the original fault still present. When all it needs are half a dozen connector contacts that cost a few quid each.