I have a 05 gmc 1500 and yesterday my message board said that my gas cap was not tight. So a few miles down the road the check engine light comes on. I got home and sure enough it was loose. How do you get the check engine light off?
Check Engine
- Thread starter wernerjd
- Start date
Molson02536
New member
Your Check Engine light will go off after three start up, unless there is an issue with your EVAP.
On 1996 and newer vehicles, the OBD2 system monitors the fuel system for fuel vapor leaks to make sure no hydrocarbons are escaping into the atmosphere. The EVAP monitor does two things: it verifies there is airflow from the EVAP canister to the engine, and that there are no leaks in the fuel tank, EVAP canister or fuel system vapor lines.
The OBD2 EVAP monitor runs once per drive cycle and only when the fuel tank is 15 to 85% full. The EVAP monitor uses a "purge flow sensor" to detect leaks as small as .040 inches in diameter on 1996-99 models, and as small as .020 inches on most 2000 and newer vehicles.
If OBD2 detects a leak when it runs the EVAP leak check, it will set a fault code in the P0440 to P0457 range.
If you find a P0440 fault code (large fuel vapor leak), remove the gas cap, inspect the seal on the filler tank inlet and the underside of the gas cap for any nicks, debris or damage. Then screw the gas cap back on and make sure it clicks at least once to assure a tight seal. If a fuel vapor leak at the gas cap set the P0440 code, the fault should clear and the Check Engine light go out the next time the EVAP monitor runs. If the light stays on, the problem is either a bad gas cap or a large vapor leak somewhere in the EVAP system (most likely a leaky or loose vapor hose).
