Gas cap and CEL

[stknrdr]

I forgot to fasten gas cap after fueling issue. Drove around with the cap unscrewed until the CEL light came on. The code references Evap emissions system. After refastening the gas cap correctly I figured the CEL would go away after several start/stop sequences. It has been approx. a dozen or so cycles and the light remains. Do I need to have it reset, or will it eventually go out when the situation has not existed for a specific period? Thanks. 2004 996 C4S.

[Loren]

:welcome:

Check the o-ring on the gas cap. Replace it if it has cracks or shows wear.

If the o-ring is fine then it is time to read the fault code(s) and report back here.

[xmac]

Provided there is no other problem, like the gas cap o-ring Loren mentions, it is supposed to clear after "3 trips," but since a "trip" is defined by the car manufacturer, it will take more than just 3 starts (or a dozen cycles) of the car to clear. Just like most laws, the regulation does not give specifics on the 3 trip requirement:

"Misfire and fuel system faults require three trips with “similar conditions” before the MIL [Malfunction Indicator Light] is turned “Off.” These are trips where the engine load, RPM and temperature are similar to the conditions present when the fault was first found."

Since you know the cause, I would just drive it some more and let it clear itself. It will stay in memory as a fault which can be cleared the next time at your shop or with a personal diagnostic tool.

[goldenwarrior1]

Here is a copy of the OBDII drive cycle requirements and the Flags set by each.

[stknrdr]

Thanks all for the posts. I have been away on vacation, or I would have responded earlier. As Loren mentioned, I checked the gas cap o-ring and it was undamaged. I drove the car several more times, but the CEL remained. Went to the local auto parts store and asked to borrow the OBD tool. P0455, Evaporative Emissions System Fault was the code read by the tool. I reset the light and it has remained off. Still, I wonder just how many "trips" I would have had to made in order for the system to reset itself. Thanks again.