Ready to go on vacation and the &$#% check engine light comes on!

[RProsser]

Hey all. We are about to head for Lake Powell for some water skiing and the damn check engine light has come on our '97 C280 (silver/dark leather w/65K mi). Hoping you can shed some light.

I suspect the light means the mass airflow sensor or one of the (rear?) 02 sensor, but would like to confirm first. The nearest dealer wants $100+ to read the codes AND I have to drop it off. I called a few of my local San Diego County Peb Boy shops. Only a few do it, and those have to make an appointment because the tech that does it is not always in. Oh, and it'll be $85 bucks. Still no way to get a fast diagnosis. I can't wait three days.

FYI: For good measure, I checked the gas cap, the throttle position sensor and then pulled the MAS and sprayed some carb cleaner on the hot wire, then I climbed under the car to inspect the two 02 sensors. Everything is intact. I fired up the car, and took it out for a romp. It runs great! In fact, it hauls ass for a 2.8! The light is still on, but it idles and shifts fine and I can't find a damn thing wrong with it.

So what's this about an "onboard diagnostics" -- is there some kind of DIY utility on the car that I don't know about? I know tons about Porsche, but not near enough about MBZ. Guess that's about to change.

Deductive reasoning: all the parts guys I spoke to today say the MAS is a regular sales item. It's a 3-minute replacement part. That's the upside. The downside is that the friggin' thing costs $250±! The same parts people I polled do not stock the front 02 sensor -- only the rear, so that tells me the fronts do not go out often. The upside is that the normally stocked 02 sensor costs $125±. The downside is that it looks like a total pain in the @$$ to remove! It's in the middle of the "Y" at the back of the catalytic converter. How the heck are you supposed to get a wrench on THAT!?

Ready for a family vacation, so any ideas would be very much appreciated!