I already posted this in this thread https://mbworld.org/forums/newreply....te=1&p=5827533 , but this probably should have its own thread:

I just got done fixing the P0455 "everything seems to be working" EVAP problem. There are a lot of "guesses" on the net to what the actual issue is that lights the CEL around the net. You're looking to diagnose a "gross" leak, meaning:

a) the cap is off,
b) the EVAP purge solenoid is not sealing (under the hood),
c) the lines are broke or disconnected
d) the canister is cracked, or,
e) the EVAP canister vent valve (behind the rear passenger wheel, in the canister) is not working properly.

It is really simple to diagnose on a GL. You don't have to smoke the system either:

0) get a vacuum kit at Harbor Freight.

1) connect the vacuum to the vent hose and pull a vacuum

2) if vacuum DOESN'T hold, then:

3) go to your EVAP purge solenoid under the hood and pull vacuum from the fuel tank side. if you can't get vacuum...then that is most likely the problem.

4) If the EVAP purge solenoid holds vacuum, then it is either the line or canister (which are both the least likely to be the problem), OR,

5) the gas cap (which the code, message center and blinking fuel light say it is). This is a cheap $10-$15 part at your LAPS, but most likely won't fix the problem.

6) if vacuum DOES hold, then it is your EVAP canister vent valve.

Let me tell you why I know this issue is most likely the canister vent valve. The valve closes when the car performs the EVAP test. There is a little rubber seal, probably the size of a nickel, that the solenoid plunges forward, closing off the vent to the atmosphere, thus allowing a vacuum to be pulled. What happens is that the rubber seal loses its sealing capability over time or if liquid gas gets to it, i.e., over filling your tank...sound familiar?

What I did was to let the valve soak in AT-205 solvent for an hour to soften the seal back up. I tested the valve w/ 12 volts off the battery to see if it would actuate freely, then reinstalled and cleared the code. My wife drove it to take my kid to softball practice (about a 80 mile round trip). Got a green light on the OBDII!

So a 5 cent rubber seal will cost you hundreds if not thousands of dollars...if you have to take it to the shop, get it diagnosed and then replaced.

Part #: 1644703193 ~$100 on eBay.

 

2007 GL450 75k
I used to have the Gas cap open message that would lead to Check Engine light.
I added an extra O ring to the gas cap and press it hard to shut each time I filled gas.
Escaped the the Gas cap open message for about a year.
Now the check engine came on by itself.
I pulled the code with an OBD scanner.
Came out with P0455.
Trying to check the EVAP canister vent valve behind the Rear Passenger wheel.

Here is what I found. I will try it this weekend.
Hope this helps the rest of us who has the same issues.

http://workshop-manuals.com/mercedes...ion/page_6024/

http://workshop-manuals.com/mercedes...ion/page_6025/

 

Where is the vent hose (step 1), evap purge solenoid (step 3) located on a 2010 GL450? I just got a P0455 code and want to start diagnosing it. Thanks.

 

How do you get the canister vent valve off? I’m trying to tackle this and I’m not familiar with how to get it off. Does it just pull straight out or does it twist out? Thanks in advance!

 

This is part # for purge solenoid under hood

EVAP Canister vent valve is 000 470 86 93

 

Quarter turn