Check Gas Cap warning
Thread Starter
Newbie
Joined: Mar 2021
Posts: 3
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From: Greenville, SC
2002 Mercedes g500
Check Gas Cap warning
I have a 2002 Mercedes g500 and continue to get the "Check Gas Cap!" Warning light with flashing reserve light. This warning goes away after I turn car off but then the Check Engine light comes on. I have replaced the gas cap, the purge (solenoid) valve and the vent canister valve. 2 different body shops have checked for codes and get nothing.
MBWorld Fanatic!
Joined: Oct 2019
Posts: 5,156
Likes: 1,770
From: Colorado
G550
Gas caps are the usual suspects inasmuch as failure to securely seat them can occur after any fillup. The gas cap code can be caused by any fuel system pressure loss. The purge valve is another potential point of failure. Another forum member was having this problem on a brand new G63, and it was eventually traced to a pinhole somewhere in the gas tank. Highly unusual, but an example of what can go wrong. The only way to find the point of failure is to take the vehicle to a shop that can do a smoke test. A visible gas is pumped into the fuel system and the mechanic searches for where visible gas is escaping. Probably not cheap to diagnose or repair, but the only solution other than to yank out the check engine light bulb.
MBWorld Fanatic!
Joined: Nov 2002
Posts: 1,028
Likes: 133
From: Massachusetts
2018 GLE350, 2014 G550, 2000 SL500, 1980 TR8, 1995 E320 Cabriolet
Yes, a faulty pressure sensor is a diagnosis of exclusion - rule out all of the other causes via a scan/smoke test and that is the only thing left. BTW, I have a new one for sale at a discount if I can find it.
