Check Engine light off and on
 

The previous oil change left my engine about a quarter guart over full and we left it for the duration. Corrected during the last change, I still fear some damage to the oxygen sensors. Now my check engine light comes on for a day or so then goes out for several more days. Just annoying. It seems to come for no particular reason. I have disconnected the battery for a minute or two to reset the computer and that always turns the light out, again for several days to a week. Then its back again. The gas cap is always wet, and fits correctly.

2001 SLK 320. Vehical has a new fuel filter (and was doing this before and since), clean K & N air filter elements, 81000 miles, runs great. My gas mileage has been good as I drive a lot (125-200miles/day).

Any ideas without heading to the shop? Charcoal filter? I have a new set of Bosch plugs ready to go in.

RE: Check Engine light off and on
 

it's not often for the 112 engine to have the "check engine" lamp on unless the engine is running rough.

it can be an O2 sensor too. it's something that can make the mixture lean or rich.

the basic setting for maximum/minimum deviation before the CEL to come on is 0.2 milliseconds. too sensitive. i always replace those to 1.5 to give more allowance just in case the gasoline quality is not so good.

RE: Check Engine light off and on
 

The car runs smooth. At a traffic light, I get a little lag or hesitation upon first hit of the gas. It acts like it is thinking about which gear to start in, but always begins in first and accelerates smoothly. My ford (also fuel injected) never hesitates, it just responds. A bad fuel mixture would cause this hesitation. Perhaps it is time to pull codes and due a minor tune up.

RE: Check Engine light off and on
 

I was just going to say it's probably your O2 sensor...but...sleepwalker beat me to it! When was the last time you actually had a tune up done?