Is there anything else besides a bad gas cap that could trigger this light? If I buy a new gas cap, do you think it will make it go off and how long might that take? The car has about 150,000 miles on it.”
Halderman: The check gas cap message comes on if the system detects a leak in the fuel system. If the cap looks normal and seems to be okay, then try driving the vehicle for a week or so and see if the message goes away. It will not go away until the system does another self-test. The self-test has to be performed under very strict conditions such as after 8 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 the warning light off using a scan tool but be prepared to pay for this service. If the light comes back, have a technician check the cap for leakage and 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.
James D. Halderman is an ASE-certified master technician, a member of the Society of Automotive Engineers and the author of 12 textbooks. Submit questions to jim@jameshalderman.com or follow him on Twitter @jameshalderman, or write him in care of: Wheels, Marketing Publications Department, Dayton Daily News, 1611 S. Main St., Dayton OH 45409.
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