Mary, I am guessing that this is your ist check engine light issue. How many miles on your S40? Most, but not all of the check engine problems are related to the cars emmissions. What your mechanic did is stupid and illegal!!(If he really did cut the wire) The check engine light can go on if you don't screw your gas cap on correctly or remove it with the engine running. I would take it to a Volvo dealer to get the fault correctly read. My check engine last came on around 55-60k, I have 99,900 now. I don't remember the fault code but what happens a lot is that your check engine system can get a "software download" to fix your problem....kind of like a Windows 95/ME/XP update, only alot easier and safer! Good luck, Bill