I bought a 2000 Volvo s40 with 85,0000 2 months ago and it's had a lot of problems. I took the car to a mechanic because the passenger headlight didn't turn on, and the car doesn't turn off if the parking lights are on. The mechanic told me it was a bad CEM. I sent my CEM to Xemodex for diagnostics a couple weeks ago and they said that repairing the CEM would only fix the headlight problem.
The car turns off normally if the headlight switch is turned to "off" or "automatic". The dashboard flickers if the parking light switch is on.

I posted a video of the problem.

Has anyone else had a problem like this? Any suggestions?

 

when you say "parking light switch" do you mean the headlight switch being set to the parking lights position? Also does your car have fog lights?

If the CEM has been replaced/rebuilt that will cover the low beam relays (high beams are on a separate path external to the CEM) so the next thing to consider is the switch in the dash. I may actually have a spare dash switch for a 2000 S40 - PM me if interested. It's pretty easy to replace... If you have factory fog lights then there may be some additional points to check out.

 

The dial on the driverside dashboard where the light control settings are. The dashboard flickers whenever I turn the dial to the "parking lights" setting. The dashboard flickers even if the car is off and the key is out of the ignition. The car doesn't have fog lights. Which switch in the dashboard are you referring to?

 

It's a little confusing, because the video shows the headlight switch in the off position (not the parking light position), and the flickering occurs there.

That's an "interesting problem", and it's clear that there are some crossed circuits there somehow. I don't have any diagrams / info for your model S40, but often when there's a really strange "multi-system" problem, it ends up being a bad ground (since lack of a proper ground can cause voltage to "leak backwards" through multiple sources instead of finding its normal path to ground through the activated circuits, like the headlights.

I'd put the car in "flicker mode", and then use a voltmeter to check for ANY voltage between the battery's negative terminal and the engine block and the body. If you're reading more than a couple hundredths of a volt, look for the bad ground.

 

Thanks for the suggestion. I'll try this. Hopefully it works.

 

If the problem is the CEM and they order a new one from Volvo, what are the odds this will be the only issue electronically? I recently got one for my son and this is the issue, and the guy is having this taken care of, but I want to know My son will not be stranded somewhere due to electrical failure. Went with the volvo BECAUSE it had such high safety ratings, thanks for your input ahead of time

 

The CEM is where several relays are located and those like any relay can burn out. On the 2000 S40, they are not paired to the car so you can go and buy one used and drop it in yourself. The CEM is the gray box under the dash over by the hood release and it has a couple of thick cables that snap in. When I replaced mine, I paid $65 for a used one and it has worked ever since. That said, you could also have a bad headlight switch, again easy enough to find a used one on eBay or in a yard - there should be a YouTube vid on how to install the switch. Beyond those two parts, if you have something flickering then you will need some more diagnostics - ie is there a solid ground (as Habbyguy noted? - time to probe with a light pen/multimeter. Can you make the flickering go away/appear by tapping things?

You may be able to find a PDF of the Haynes manual online or similar with a wiring diagram. I'd also inspect things like the connectors to the headlights and bulbs etc as they have a lot of heat to put up with which can crack the sockets.