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My check engine light turned on. I used my OBDII scanner and got back the codes P0441 and P0455, which is sometimes caused by a loose gas cap. I checked my gas cap and it was indeed loose. I tightened it and the light went off.

However, when I use my OBDII scanner now, it still pulls up those codes.

What should I take this to mean? Is the code persisting even though the problem is fixed, and I just need to clear it? Or, does this mean that I need to replace the gas cap or do something else, and the light turning off was not meant to indicate the problem was solved?

Should I clear the code and wait to see if the light comes back? Should I buy a new cap and then scan to see if the code persists?

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  • Welcome to Motor Vehicle Maintenance & Repair! Oct 5, 2023 at 20:32

2 Answers 2

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Did you try erasing the codes? Most codes are not persistent, meaning they will not remain after the ECM is reset. Even though they are non-persistent, you still have to get rid of them.

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If close to state required emissions inspection, DO NOT RESET ANY ERROR CODE by battery disconnect or reader reset button. All this does is erase stored emissions parameters that keep the check engine light off as self test emissions are performed on every engine startup and drive. Any error related to emissions is automatically generated along with the CEL indicator. Resetting before state required emissions inspection will automatically fail because a drive cycle is needed to restore erased parameters, taking as much as 50 miles of varied local and highway traffic/speeds. If emissions inspection isn't part of your state inspection or won't occur for a few months, resetting may help but not if the error wasn't corrected. And then there are pending codes, correcting the error, turning off the cel indicator but pending for several drive cycles. A drive cycle is starting, driving, and shutdown. After several drive cycles and the error doesn't reappear, the code disappears automatically. Many readers do not differentiate between live and pending errors. Yours may be a pending error and won't go away until two more drive cycles.

Resetting, manual battery disconnect or reader reset, erases learned emissions parameters back to factory defaults. Coolant temps, intake air temp, map/maf/evap/O2 sensors are monitored and must output data within a range to meet emissions requirements. Each sensor outputs right from ignition on time, thru a driving cycle and memorized. This doesn't occur immediately, hence up to 50 miles of driving needed whether all done in one drive or several daily drives. Better readers display data as readiness monitors and can display which ones passed and which ones haven't until all pass with a reader indicating READY or NOT READY; telling the diyer the vehicle is ready for emissions inspection.

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