I don't think I have the codes written down anywhere and if I have to get them I might as well have the mechanic that gets me the code fix it, shouldn't I? I just thought that maybe a new gas cap would solve the problem since it happens when I fill the tank. Thanks anyway.
If you want to take it back to them, find out the codes and make sure they write it down so if the light does come back on, and it sets the same code then they should not be charging you again for the repair. If you have some paper work for the repairs thay have made already, then the codes should be written down as part of there stroy for the repair.
If the gas cap was bad, the light should stay on all the time and not go off when you put in gas. You might just want to replace the cap and see what happens, the caps are cheap and you can get them at any auto store, just stay away from the locking caps, they cause more problems with check engine lights. It may be a fuel level sensor that is going bad inside of the tank, this will set a p0463 code and may clear up when fuel is added.
Let me know if you find ou any code information.
The fuel level sensor is inside of the fuel tank, this is the sensor that tells your fuel gage how much fuel is in the tank. If you are having fuel gage problems then the sensor is bad. If not, there maybe something else wrong. The fuel level sensorneeds to be replaced by someone that has at least light car repair skills since the fuel tank needs to be removed.
Disconecting the battery will not clear the codes on most cars, if you go to a auto parts store, they can clear the codes for you for free, I would have them write the codes down before they clear them, this way you know what codes are setting if the light comes back on.
If there is a bad spot on the sensor, lets say when the fuel level gets to 1/4 full, the snesor may have a open circuit, when you fill the tank, the sensor moves due to the float in the tank, this then makes the sensor read correctly again. The reason this will set off a check engine light is due to the engine computer performs a evap leak test for the fuel system (the computer checks for leaks in the fuel tank such as the fuel cap). The computer can only run this test when the fuel level is between 3/4 and 1/4 full. If the fuel level sensor is going bad, then te engine computer does not know how much fuel is really in te tank which can affect the test results.
This is only a possiblity and unless the code P0463 is set, then this is only a guess.
DTC P0463 Fuel Level Sensor Circuit High Voltage Circuit Description
The vehicle control module (VCM) requires an accurate indication of fuel level for evaporative emission (EVAP) system diagnosis. The fuel level in the fuel tank changes the rate of vacuum decay for the EVAP system leak DTCs.
The fuel level sensor changes resistance based on fuel level. The fuel level sensor has a signal circuit and a ground circuit. The VCM applies a voltage of about 5 volts on the signal circuit to the sensor. The VCM monitors changes in this voltage caused by changes in the resistance of the sensor to determine fuel level.
When the fuel tank is full, the sensor resistance is high, and the VCMs signal voltage is only pulled down a small amount through the sensor to ground. Therefore, the VCM will sense a high signal voltage (fuel tank full). When the fuel tank is empty, the sensor resistance is low, and the signal voltage is pulled down a greater amount. This causes the VCM to sense a low signal voltage (fuel tank empty).
The VCM uses the input from the fuel level sensor to calculate the fuel level in the fuel tank. This information is then sent to the IPC through Serial Data.
The diagnostic will not run when the tank is more than 85 percent or less than 15 percent full. (This sensor signal disables the misfire when the fuel levels are less than 15 percent).
If there were oxygen sensor codes, then the fuel level sensor is most likely not the problem. Oxygen sensor codes can be caused by many things, from a leak in the exhaust system, bad wire, blown fuse, improper fuel, engine that runs rich or lean just to name a few.
I have seen oxygen sensor problems that are set by a bad oxygen sensor and was replaced with a aftermarket sensor, only to reset the code. Aftermarket oxygen sensors are a unviresal fit, not a direct replacement. Only GM has the direct replacement sensor and should be used for best performace. They cost a little more but for a good reason.
Let me know if you need more info, I'am here to help.