Volvo S40 Forum : “Check Engine Fuction”

Lets you know if your emissions system or electronic engine controls are not operating properly.

I've had several mechanics tell me it could be a whole mess of reasons, and that Volvos are famous for their check engine lights that come on for little to no reason, and then can't be taken off without very expensive equipment. Most of the time if it's on it's not a big problem, unless you want to pass emissions.