Check engine light on due to Tank Cap Loose - Page 3 - Mercedes-Benz Forum

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post #21 of 22 (permalink) Old 07-27-2007, 05:50 AM
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I had this same problem and it turned out to have nothing to do with the gas cap. All the warning means is that there is a pressure loss somewhere in the fuel system. In my case it was charcoal cannister valve.
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post #22 of 22 (permalink) Old 07-27-2007, 11:19 AM
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These other replies (and Mike's in particular) make clear that code diagnosis is often an ART, not a science, which explains the spreading of general misinformation that "the codes are wrong" (example of tomfoolery as requested).

For example, the code that started this thread can mean several things, such as the evap canister, the bank leak, etc., but in these cars it is *most often* a failing gas cap seal/vent. Thus, typically when that code is seen the first response is to replace the gas cap. On other makes that might not be the case, perhaps their canisters are undersized, etc., so they fail more often.

In any event, at this stage of the game it's not practical to put a sensor EVERYWHERE you'd like one and then have codes that are that specific (as are the 02 sensors, for example). So you have to have the experience person to tell you what a more general code is more likely to mean.

Take care and enjoy the ride,

Socialism is a philosophy of failure, the creed of ignorance, and the gospel of envy; its inherent virtue is the equal sharing of misery. (Winston Churchill)
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