OBDII Scanner showing code after the light is gone

Question

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?

Answer 1

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.

Answer 2

Some code are stored as history codes and can not be removed. When reading the code, the scanner will indicate its status. Pending, History, Confirmed(Active-Sets light), Permanent(Can not erase, no light). Pending codes will not turn the light on until the problem is detected more than once(or what ever the codes condition is).

P0445 is a circuit problem with the purge value. Could be a bad valve or circuit problem. Key on the valve should have 12v on one wire. When the value is activated, the other wire is a ground controlled by the PCM. Of course this is without knowing what car your working on.

P0441 is because the purge is not happing when the computer expects. The PCM looks for the pressure to change in the tank by opening the purge and closing the tank vent, when it tests the evap system for leaks.

Answer 3

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.

Answer 4

It’s normal for the codes to still appear on the scanner. The check engine light turns off when the system detects that the issue is resolved, but the codes remain stored in the ECU (Engine Control Unit) as a record of recent problems. If you’ve tightened the gas cap and the light is off, the issue is likely fixed, and you just need to clear the codes. If the codes don’t reappear after clearing them and the light stays off, there’s no need to replace the gas cap.

However, if the codes reappear after clearing or the light comes back on, the gas cap might be faulty and require replacement, or there could be an issue with the EVAP (Evaporative Emission Control) system. Start by clearing the codes and waiting to see if the problem returns. If it does, try replacing the gas cap. If the issue persists even after replacing the cap, you should have the EVAP system inspected by a mechanic.