My 01 jetta has check engine light on.?

i took it the mechanic and he replaced the mass air flow and the fuel filter because the scanner it was too lean I think it said low bound exceeded . the light came back on after a day. I took it back and this time he read on the scanner that it was too rich this time. can you tell anybody what really the problem is?

1 year ago
i forgot to add that its driving slower than before and taking up too much gas I have lost about 100 miles in gas mileage, and he replaced the fuel regulator, I think that what its called.

1 year ago
but it is still the same

What engine do you have? The TDI's have a glow plug harness and glow plug problem that has that same effect. Mass airflows are a part of crap so it may still be the problem and the fuel pump on all vw's are crap also they like to short out. I could have your car scanned at the vw dealership because the don't just scan they hook the computer up to volkswagen directly and a man over in germany runs to codes and gets an correct answer. that's why they charge so much for service over there. But at least you'll know the problem from the right people.

six Years at VW

you will have a flawed sensor in your engine best bet is get it on the diagnostis machine at a VW dealer,it is more than probably an intermittent fault so may need some tests.

Check engine light is a computer generated light it so you go to the dealer or a shop and the run the diagnostics on it and see if and codes were set most shops just reset the light and charge you, the check engine light is a emission control something with the smog control need serviced, however you may be able to still drive the car its going to run the same usually unless there's a real failure of a part, NOW if the light is on and you take to get a smog test they'll fail the car because its smog related and you'll have to get it fixed, your best bet because VW need a special kind of mechanic familiar with your car to do a honest fix but get it in writing for diagnoses 1st then have them give you a price and they must guaranty it'll cure it it can get out of hand easy, and the law says it must Be someone certified in emission fix so you're better off taking to a dealer but if you can not now you may be able to still drive it, but if an oil light or charging light, or over heating light comes on you have to take imitate action to prevent damage to you car hope I assist you take care

Mine did that and it was bad spark plug wires.. It could go off some times for a while then back on. Have them put it on a computer at a VW dealership. Save yourself some $$$

oops that is what I get for now reading the whole question. But you never know someone may be taken you on a $$$$ sucking trip.

90% of the time it comes on because your gas cap isn't on tight enough. My mom had the same problem in her 02 tdi jetta, dealer also said it was the gas cap, tightin it really well after fillin up and it should go off.