The dealer replaced the fuel cap but the problem persists. First the flashing low fuel indicator then the check electronics and CEL light come on. I took it back to the dealer and they now suggest the gas tank is the problem and want to to have it replaced at a whopping $1800.

I have a data logger and can reset the CEL but it's annoying as heck. My gut tells me it's not the tank and if I add some duct tape to the cap and place it on the problem stays away longer.

How can I tell if it's the sensor that's wrong? or, how can I just eliminate this vac test and is that a bad thing?

HELP!

Tommy in New York!

Tommy
There are a few things it could be. I agree it's doubtful it's the tank, I don't know if I've EVER replaced a tank on a 210. Once I replaced one on a 202 because a cell phone installer drilled a hole throught the floor pan and into the tank. (I assume this isn't the case here ).
The few thinks you mainly see: The #1 culprit is called the "charcoal canister shut-off valve". It's located attached to the top of the charcoal canister, which is behind the rear of the wheel well trim in the right rear wheel well. To test this requires a good vacuum pump and a tester which can read the fuel tank pressure/vacuum (such as the MB SDS tester), and also get into system activations. What you do is attach the vac pump to the purge line under the hood, activate the shut off valve, and draw vacuum, while monitoring vacuum readout. You should be able to pull about 25 mbar of vac, then plug off the vacuum, and should hold above 20mbar after 1 minute. If it won't pull ANY vacuum, that's when you use a big crimping pliers or two and start pinching off evap hoses to determine the leak. What you'd want to pinch off first is this charcoal canister shut-off valve itself (the one you "closed" electrically with the "activation" feature), and see if it'll then hold vacuum, usualy that's it. I'd say if you want to "throw a part" at the problem, with about 75% probability the shut-off valve is the problem. OTHERWISE the charcoal canister itself can cause this problem. There are a few other possibilities. I wonder if a proper test has ever been done?
Gilly

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I had same problem with 99 ML430. It was a wire to the charcoal canister shut-off valve.
See this thread:
Check Engine Light / Codes from diagnostic
I don't know if your car has similar connector outside?
Mike

Thanks for all of the responses. I might just go ahead and replace the part to see if that solves the problem.

Cheers!

I replaced the Canister Purge Control Valve and reset the computer with my OBDII datalogger and the problem has yet to recur after 40 miles of driving. If this actually fixes it, I will have solved the problem for less than $60.

Thanks again for the super technical support on this thread.

I'm having the same problem on my 1998 c230. Does anyone know if my canister purge valve is also behind the right rear wheel? Also, how big a job is replacing it?

Thanks.