'14 GL450 EVAP leak detection assembly - where?!
Thread Starter
Junior Member
Joined: Feb 2022
Posts: 23
Likes: 7
From: Philadelphia, PA
'14 MB GL450, '14 Audi Allroad
'14 GL450 EVAP leak detection assembly - where?!
This weekend the check engine light popped up, with the dreaded P0442 and P0456 codes (Very small leak and small leak detected). The P0442 (very small leak) also included "An internal fault exists", and I am unable to clear both codes. I realize I need to do the approximate EPA drive pattern enough times for the computer to register any repair and turn the light off.
I have started troubleshooting the problem, here's where I'm at so far.
1) I pulled the purge valve off the car and tested it mechanically and electrically. It is good.
2) I pulled the charcoal canister vent shutoff valve and double checked the o-ring sealing it to the charcoal canister. Unable to very actuation off the car. The wiring diagram is a little dodgy on this one and I don't want to fry something applying current to the wrong side.
3) I did a smoke test. From the purge valve to the intake, no leaks. From the purge valve to the gas tank, only place I could find smoke coming out was the charcoal canister shutoff valve (It it made in such a way that it appears to be designed to bleed off air, and since its at rest position is open, I believe this is an acceptable result, and I have also effectively eliminated an actual air leak.
My next step is to take a look at the EVAP leak detection assembly and the pressure sensor. I know the pressure sensor is on top of the gas tank, but where is the leak detection assembly?! I have checked WIS with no luck yet. I don't understand why they bury things, but I can't find it under Group 47 which is where it should be I believe.
Off to check every section of WIS until I can find it. I'm all ears if anybody has found it.
I have started troubleshooting the problem, here's where I'm at so far.
1) I pulled the purge valve off the car and tested it mechanically and electrically. It is good.
2) I pulled the charcoal canister vent shutoff valve and double checked the o-ring sealing it to the charcoal canister. Unable to very actuation off the car. The wiring diagram is a little dodgy on this one and I don't want to fry something applying current to the wrong side.
3) I did a smoke test. From the purge valve to the intake, no leaks. From the purge valve to the gas tank, only place I could find smoke coming out was the charcoal canister shutoff valve (It it made in such a way that it appears to be designed to bleed off air, and since its at rest position is open, I believe this is an acceptable result, and I have also effectively eliminated an actual air leak.
My next step is to take a look at the EVAP leak detection assembly and the pressure sensor. I know the pressure sensor is on top of the gas tank, but where is the leak detection assembly?! I have checked WIS with no luck yet. I don't understand why they bury things, but I can't find it under Group 47 which is where it should be I believe.
Off to check every section of WIS until I can find it. I'm all ears if anybody has found it.
Senior Member
Joined: Jan 2015
Posts: 306
Likes: 78
gl450
Sorry if I state the obvious - but did you check the gas cap? I had this code on my 2013 gl450 last year, and in my case it was the gas cap - apparently they deteriorate after about 10 years. Replaced it and haven't seen these codes since.
Thread Starter
Junior Member
Joined: Feb 2022
Posts: 23
Likes: 7
From: Philadelphia, PA
'14 MB GL450, '14 Audi Allroad
Sorry I neglected to mention the gas cap. I did check it during the smoke test and it was doing it's job fine. I pulled the cap to verify smoke was in the tank, put the cap back on and no smoke was escaping. Obviously that doesn't tell me if the cap is holding "enough" pressure, but it's a start.
I was able to clear the codes finally a little bit ago, so I'm going to roll with it and see if it returns. Could have been a fluke I guess. I'll know soon enough.
I was able to clear the codes finally a little bit ago, so I'm going to roll with it and see if it returns. Could have been a fluke I guess. I'll know soon enough.
