i have a 01 s40 and the check engine light came on.My mechanic said he cut of the light with a obd2 machine but the light came back on a few days later. How do I know this is true?

hey Mary, My wife's 2000 S40 had the same trouble with the check engine light coming on. They finally fixed the trouble by replacing the ECU computer. The tech saidthis is the main computer for the car. FOR ONCE, I'm glad I bought the extended warrenty when I bought a car. that covered the costof the whole job. I have to trust that they did the work, cause I wouldn't knoe this computer if it jumped out of the trunk and bit me! The lamp hasn't come on again, so they either fixed it, or just removed the lamp from behind the instrument panel ( my wife's idea).

If the lamp comes on before you start the car duing the "lamp test" function, then the connection and lamp are OK.

If the mechanic didn't tell you what the reason was, go to Autozone. They will read the code for free.

Then you will know why yhe CEL came on in the first place.

mormit
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85 245DL 255,000mi V15cam 'Old and Rusted', 02 S40 'New Hotness'

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

If he just turned the CE light off w/o correcting the problem that turned it on, it will come back on. The CE light comes on when the engine computer detects a fault in a number of systems (engine, tranny, ABS etc.) . THe OBD-II code reading machine displays the fault code(s) that points to the defective part/system. You need to have him re-read the system an write down the fault codes.

bls