drb930

Are you re-setting the light each time with a scanner?
The purge valve could be checked by re-moving the valve and putting power and ground to the terminals and it should click, like solenoid.
You might want to put a resistor in line with the power to check the valve at less than 12 volts.

Thanks,
Dave

Glyn M Ruck

What codes are you getting?

c240classic

Yes i am resetting the light everytime. Can someone please check something for me so that i can be sure i am on the right track. After driving the car for 10 minutes or more, when you open your gas cap up to put in fuel, do you guys/gals hear an audible vaccumm whoosh?
I am pretty sure i used to hear it before this problem started happening. If that is the case then i have three possible options

1) the vaccum line from the fuel filler to the EVAP canister is leaking or the fuel filler itself is leaking air.

2) the evap canister cannot hold a vaccum or the shut off valve to the canister is not opening to let anything pass through from the tank to the canister.

3) the purge valve is not pulling anything from the canister either because it is not opening or there is a leak in the vaccum line between the canister to the valve or from the valve to the intake manifold.

Here is another one of my stupid ideas, please let me know why this will not work.
If i bypass the shut off solenoid valve on the evap canister. What i mean is connect a vaccum line from the fuel filler neck to the purge valve, leave the shut off solenoid electronically plugged in. Let the engine run for 10 minutes. If i open up the gas cap after that, if i get a whoosh, means my shut off solenoid is bad.
If i still dont get a whoosh,

If i leave the purge valve plugged in so that the ecu does not detect its un-plugged. Connect a vaccum line straight from the bottom of the evap canister to the intake manifold (essentially bypassing the purge, so i am purging all the time). If i do this for 10 minutes, open up my gas tank and hear a whooosh, it means my purge is not working right.

c240classic

P0442, Small Evap Leak.

It takes 2-3 days for it to come back but it does come back! Feel like putting my fist through the dash when the check engine light comes on :P

Glyn M Ruck

These are a real swine to locate. Can be something as simple as a new gas cap to the inlet tube (LILBENZ's problem), to the charcoal canister to any joint or pipe in the EECS. We have been trying to track one on nlpamg, one of our moderator's car for over a year & no luck. The best way is to smoke test the system to find the leak. On no account pressurise the system with compressed air. This is extremely dangerous with gasoline present. I've posted all the diagrams previously. If you can't find them let me know.

Good luck

mblkout23

(I dont have a coupe.)
Can you remove the fuel filler neck on the sedan with the same procedure?
I fuc*en hate my check engine light.
I just wasted $350 dollars, so that the dealership can change my stupid purge valve.
Im sure it only took them 5 min to change. The light came back on the day after.
I hate the dealership.
Well now they are telling me its the fuel filler neck.
I would do the work on my car, but I have never worked on mercedes vehicles.
I dont want to mess something up and regret it. Its not a dodge or Chevy.
Well this sucks.... I dont know what to do?

mleskovar

It's not 'almost' or they would have repaired it properly.

Guess what, Mercedes is built with the same fasteners (for the most part) as all cars. If you search, start by really reading this whole post, you'll find....it's been covered several times and even with pictures.

mblkout23

thank you!

drb930

Try taking off your passenger rear wheel and the plastic nuts and remove the cardboard inner fender and see if you can see the fuel filler neck there, if so it's easy to take out.

Dave

mblkout23

I will attempt this weekend. Thank you sir.

LILBENZ230

This doesn't surprise me. When my car threw this code at 35000ish miles, the dealership replaced the purge valve and a few other parts before replacing the fuel filler neck (which actually fixed it). Maybe you should demand a refund since the purge valve was not bad? I would.

Glyn M Ruck

Has a TSB ever been put out in the US for this darn leaking filler neck?

power-fade

I've had a long story on my CEL problem (small evap leak), and this is what the dealer did...

replaced purge valve - 4X
replaced MOT valve
replaced fuel tank
replaced updated fuel sending units
replaced ECU or ME
replaced activated charcoal canister
and finally...
replaced fuel filler neck with expansion tank

Good thing, it was all done under warranty!!!!!

Glyn M Ruck

Wow - I would have replaced filler neck or charcoal filter first! Thank heavens for warranty.

c240classic

For the guys who have had the filler tube leak, where exactly was it leaking? I am wondering if a gob of epoxy will do the trick, since it is just a small air leak. I still have this problem and have just learnt to ignore the check engine light!

fookoo303

I recently installed a new fuel pump and am now getting a p0422 CEL. During siphoning I may have damaged my filler tube. Is there any good way to check this and is this repair DIYable?

drtyjrzy

I have had this same problem for two months since I bought my car and the cel came on the next morning. needless to say I was a little upset. it is at the dealership right now, third time, first was smoke test to find out charcoal canister was bad, wait two weeks for part, second was replace charcoal canister, light came back on a day later, had to wait a week plus to get back in, another round of smoke test, just spoke with sa, replacing filler neck now. I hope this is the answer. I guess I know why the last guy traded it in. if I end up with anything else to try when they eventually get this fixed I'll post again.