Hi everyone. I have a 2001 325i with 38,000 miles on it. Last week, the "Service Engine Soon" light came on, even though the engine seems to be running as fine as it ever did, and gas mileage hasn't changed.

I know there are a bunch of reasons this light can come on, but wondered if you guys have experienced this and if so, what the cause was and how much you had to pay to get it fixed.

Seems a little early for an oxygen sensor replacement. . .

One reason is not having the gas cap fully tightened. Check that first. The light may or may not go out by itself if that is the problem.

 

Do a search NOOB!
Car should still be under warranty, no?

I have to assume that you DID know about the gas cap and have tightened it. If so there are a hundred other possible triggers for the check engine light that does not affect drive-ability (or doesn't rear it's ugly head until later).

Assuming you are correct that the engine runs just as fine as ever, that rules out the ignition coils, which is a common cause for the CEL and is a very common failure item on this particular vintage. There are two other causes that I know of that does not affect drive-ability. First is the Camshaft Position sensor. When this fails it'll either cause an intermitten check engine light (if the CEL goes off by itself in a couple of days but returns later with no provacation) or if both sensors fail the CEL will remain lit. Another is the throttle potentiometer, this will cause the CEL to come on permanently but does not affect drive-ability at all.

Those are the only two causes that I am aware of that does set off the CEL but does not affect drivability. There are probably hundreds of other problems that may potentially cause the same problem/symptoms you described, and there is no way to diagnose them unless the car is hooked up to a GT1 or equivalent diagnostic machine.

 

Thanks for your advice Hack. I did check the gas cap and that wasn't it. I know I'm going to have to take it to a dealer to get checked, but wanted some education on the subject before I do. Appreciate your help.

 

I posted in another SES thread that my problem had to do with conflicting codes. IIRC they just reprogrammed the DME. So far so good ... knock on wood ...for the last couple thousand miles. I was getting hesitation between 2.5k and 3k and was especially noticable in 4th or 5th gear (step).

 

325i

service engine soon light come on every morning and only when its cold only. the car is little shaking and sometime the car die. the light never come on in the summer time. any suggestion would be greatly appreciate.

 

Anytime the engine light comes on, there is a code associated with it. Places like Autozone can read the code for free. Without the code is almost impossible to tell what the problem may be.