My wife drives a 1998 C230 we bought a year ago. Its got about 65k miles on it. About 5 months ago the CEL light came on for a day. Recently it has come on and stayed on for a month then went off. Its back. The Autozone pulled the P0170 code. the car runs fine. It even passed Massachusetts emissions with the CEL on. The Autozone guy cleared the code. If the car runs fine and it comes back, do i really have to do anything if it runs fine, or it is it possibly a matter of time when it will start running lousy.

Not sure on your question, but I've got one for you. Out of curiosity, did the CEL come on after you changed the engine air filter?

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Michael

1988 300 SL (5 Speed)
1994 E320 Wagon
1997 C230

My question is if the car is running fine do I really have to be concerned with this CEL. If it is a situation that will get worse then yes I will need to do something about it. I have seen posts where peole replace the MAF even if the car runs fine. Why bother. Just looking for some guidance. I put in a new filter when I bought the car exactly 12 months ago. I put a new one in this month while the CEL was on hoping it might be the problem.

It is usually an indicator that worse will be coming. It also may exist at the moment but you just haven't noticed. It might show its ugly head one day as you are trying to pass a car at 60mph. I have noticed that most of the cars I see with that code and a AMM problem have flat spots in their acceleration, eventually up to the point that the car falls on its face with a sudden full throttle acceleration.

There also is a more technical/economical reason. Your car reaches that code when its ability to center the mixture control range is reached. This at first doesn't matter to anything. Whether it has more ability to correct lean than rich doesn't matter as long as it doesn't need that extra correction (the sudden passing of a car might find one of those times). Eventually it is likely that the lack of ability to center will mean that it doesn't have the ability to maintain closed loop control. This still probably won't be felt except in those special conditions, BUT, your catalytic convertor will know. It is absolutely imparative that a modern cat see an exact average mixture that equals the precise chemical portions to effect the burning process with nothiong left over. Excess hydrocarbons, which happen anytime control isn't maintained, will ruin a cat in a short hiway trip.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician