Q: gas light loose and check engine light comes on I replaced gas cap and the issue still happens

asked by on October 27, 2016

It says gas cap loose and check engine light comes on I replaced gas cap and it still is the same what could it be.

My car has 167000 miles.
My car has an automatic transmission.

The gas cap is the most common source of evaporative emissions, which would be a reason the check engine light would come on. The evaporative emissions system is designed to limit the evaporation of fumes from the fuel in your fuel tank. We all know how easy it is to forget our gas caps at the gas station or simply not tighten it tight enough. This is the reason for the gas cap loose illumination. It often saves customers an unneeded trip to a shop for a gas cap.

Your evaporative emissions system consists of the fuel tank, vapor canister, several pressure sensors, valves and many feet of hoses running from the motor to the fuel tank. If there is a leak in any part of this system, the check engine light will turn on. At this point you need to read the code with a scanner and follow the diagnostic flow chart for that code.

It is often necessary to connect a smoke machine to the emissions system to locate the leak. Smoke machines are not cheap, so most people won’t be investing in one to diagnose their vehicle. There really isn’t another good technique to find a leak in an evap. system. You can do a visual inspection, but this will only reveal a problem if the leak is very large. The code will let you know if it is a large or small evaporative emissions leak.

If you wish to have an experienced technician to help you diagnose this, a certified YourMechanic technician can be dispatched to your location to inspect your vehicle’s check engine light and diagnose any repairs necessary.

Good luck!

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