New here & new to volvo. I just picked up a nice 2007 S40 T5. I'm having a weird electrical issue that I can't seem to pinpoint. Occasionally the cluster will quit working, no gauges, no lights besides the brake light pops up. At the same time the hvac blower will come on, the radio, windows, turn signals are all unresponsive. If I shut the car off, sometimes it will not start back up but if I wait a few seconds it will crank back up & all is normal again. Until it happens again. Sometimes it will come back on its own when driving, sometimes it doesn't. I checked the CEM connections. All looks good there. I was thinking possibly the ignition switch because the 1 fob I have it messed up but not sure because it seems to start & work properly 95% of the time. I did notice that if I unplug the radio screen, the dash quits & the brake light will come on until I plug it back in. The blower also comes on as well & the wipers turn on. I was hoping someone here had some advice for me. I am mechanically inclined but electrical is my enemy. I'd hate to start throwing parts at it

 

Unfortunately you have found out why the car was for sale.

If electrical is your enemy - you may have a hard time solving your problems - by throwing parts at it. It's going to take someone who understands modern CANBUS electrical systems and can find the common thread. If you want to tackle a wiring diagram yourself - yours can be found at volvodiag.com under the EWD tab at the top.

A good first step (I trust you have checked basics like battery connections) would be a scan with a compatible scan tool, one that can talk to and activate all the control units. The best choice for that is VIDA either with a subscription or the hacked 2014d easily found free on the internet. You might have a problem with the CEM - you would need specific Volvo codes if you end up sending it off to xemodex. Common symptoms courtesy of xemodex

 

moving the thread to the S40 forum page for more eyes. "Forum issues" is for issues with the web site :-)

 

It would terrify me that the brake lights come on and the dash goes dark when you unplug the radio display (and I was a pretty good technician in a couple previous lives). Something definitely not right. I'd suggest doing some basic high-level checks to make sure your basic electrical system is good (look for 12 volts on the battery with the car off, 14 volts with it running, and little or no voltage drop from the negative battery post to the body or engine block).

Other than that, it's going to be "interesting" to test, troubleshoot and fix.

 

If electrical is your enemy - you may have a hard time solving your problems - by throwing parts at it. It's going to take someone who understands modern CANBUS electrical systems and can find the common thread. If you want to tackle a wiring diagram yourself - yours can be found at volvodiag.com under the EWD tab at the top.