The self-test has to be performed under very strict conditions, such as after eight hours “soak time” with the temperature within a certain range and the fuel level between 15 percent and 85 percent. Therefore, if the fuel level is too high or too low, the self-test will not occur and the light will remain on.
You can ask your technician to turn off the warning light using a scan tool but be prepared to pay for this service. If the light comes back on, have a technician check the cap for leakage. If the cap is not leaking, this means that there is likely a leak in the evaporative emission control system. Testing this system usually requires that a special machine be used, so while a replacement gas cap will often take care of this concern, be prepared for further diagnostic charges and repair expense if the leak is not caused by the gas cap.
Have an automotive question? Write to Jim at jim@jameshalderman.com.
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