SL/R129: Check Engine due to bad gas cap?
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Joined: Feb 2006
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From: New England
1992 500SL, 1990 Jag XJS V-12 Conv't, 1976 Jag XJ12C, another '76 XJ12C!
Check Engine due to bad gas cap?
When I first got my '92 500 SL I had to go through state emissions inspections. Part of the test is a bench check of the gas cap ability to seal properly. While, my cap failed, and later that day my check engine light came on. The inspector was running the car for a few minutes without the cap on. When I went to buy a generic cap at the auto parts store and I mentioned not beleiving that the OEM cap had actually failed, the first thing the guy at the counter said was "Didn't your check engine light come on?" While, sure enough, I changed the cap, reset the code (by disconnecting the battery) and the light has been off since. Has anybody else experienced this? I noticed in this and some other forums people complaining about intermittent and persistent Check Engine lights, some folks spending a ton of money chasing parts and never resolving the problem. They never mentioned changing gas caps though.
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Joined: Jul 2005
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From: Toronto
1998 E320, 1994 320 SL,2000 Ford F 150.1997 Gixxer 1100
Yep, really common. Doesn't have to be a Mercedes either. We had a Pontiac Montana with the same problems. Was not really a bad gas cap. The guy at the full serve gas station did not bother to lock it past the required number of clicks.
My 944 turbo had a bad gas cap which caused a failed emissions test.
My 944 turbo had a bad gas cap which caused a failed emissions test.
Thread Starter
Almost a Member!
Joined: Feb 2006
Posts: 57
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From: New England
1992 500SL, 1990 Jag XJS V-12 Conv't, 1976 Jag XJ12C, another '76 XJ12C!
Well, I gotta learn to keep my big mouth shut! Check Engine light came on today about 3 hours after I posted this thread! Oh well, maybe I can get a new gas cap and make the $#@*! light go out on my '98 Deville instead!
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Joined: Nov 2002
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From: Massachusetts
2018 GLE350, 2014 G550, 2000 SL500, 1980 TR8, 1995 E320 Cabriolet
OBDII (On Board Diagnostics, Level II) regulations require that cars check the integrity of the evaporative control system on a regular basis. Usually this is tied to a certain number of start/engine warm-up/stop cycles. The gas cap is part of the evap system, so if it is not on or not sealing, the next time the cycle is completed you get a check engine light (this is true of all OBDII cares, not just MB). You need to get or find someone with an OBDII reader to read the P codes and locate the exact source of the evap failure.
- FD
- FD
Thread Starter
Almost a Member!
Joined: Feb 2006
Posts: 57
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From: New England
1992 500SL, 1990 Jag XJS V-12 Conv't, 1976 Jag XJ12C, another '76 XJ12C!
I've seen posts here and there that indicate it is possible to pull the codes with a simple resistor/LED device. Anyone know the process for doing this or if it is even feasible on a '92 500 SL?
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From: So. Cal.
SL500 2001 Formula 1 Edition;
This used to happen on my 1999 Olds very often. Especially if I ran the gas tank to almost dry before filling up. I would have to drive for a while and then reseat the filler cap. Then it would go away until the next time.
