HELP! 1997 E-420 P0455 EVAP Leak
 

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

I had same problem with 99 ML430. It was a wire to the charcoal canister shut-off valve.
See this thread:
http://www.peachparts.com/shopforum/ml-gl-g-wagen-r-class-unimog-sprinter/80290-check-engine-light-codes-diagnostic.html
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.

Not sure where yours is located but mine was under bonnet and it took me all of 5 minutes to change it. There were no bolts just a bracket that the valve slides over and the vacuum lines were pulled off by hand. That simple....

Tommy
You replaced the wrong part, I believe you replaced the purge valve, different part than what I discussed. It is somewhat related to the problem, but not to that particular code.
Fast Neutron, Tommy had already had his fuel cap replaced. You have to be sure the cap id good, and that it's tight and that the car wasn't driven with a loose cap or refuelled with the engine running (cap off).
I am trying to remember which side the canister is on a W202, it's in the rear wheelwell area, I think the LEFT on a 202, could be wrong. It's a "moderate" job, not easy as an oil change but way easier than.....a headgasket, does that help? Helps if you can prop up the car and remove the wheel. Need to remove the charcoal canister to get to it, and need some spare clamps for putting the hoses back on, right around 1" worm-gear clamps.

The charcoal canister SHUT OFF valve is what commonly causes this code. The purge valve itself (the part you replaced) commonly causes a code for "incorrect flow" in the purge system. Replaced LOTS of these purge valves too, but not for this evap LEAK code. Leaks codes are commonly caused by the charcoal canister shut-off valve (#1 reason), also bad fuel caps and charcoal canisters.
Gilly

It was actually Steve Brotherton that made the recommendation.

"If you just want to throw a part at it I would advise the purge valve as it is the most common cause, rather cheap and easy to change. Remember the purge valve is not tested in the vacuum test, but the tank is!"

If I didn't change the right part I hope it continues to relieve the CEL issue.

I hope it does too.......

Gilly

Have the same problem for my 97 E420. Reset the ce lights to try to get it through CT emissions. The guy said my car's computer wasn't ready to be tested. I gather they hook up their computer to my car's computer which said it was "not ready." I changed the gas cap. I guess I have to drive it a few miles to see if the ce light comes on again before I take it to CT emmissions again.