I have a 2004 Saturn VUE with 83,000 miles, 2.2-4 cyl, 5 speed manual. Just recently unknowingly lost the fuel cap and ran without it for 1/2 tank of fuel. Found the cap was missing on next visit to the fuel station and quickly purchased a replacement and reinstalled. About 100 miles later the check engine light came on and stays on. Manual indicates the light should reset and go out after a few trips but I traveled more than a few trips and the light is still on. There is no perceptible difference in performance or gas mileage. What sensor is causing this and how can I correct? Thanks
All diagnostic trouble codes have different parameters for ignition cycles before the malfunction indicator light will turn off.
In your case, it may very well be a trouble code which must be cleared manually with a scan tool.
If the light stays on, have the code confirmed to be an evaporative emissions system leak (missing gas cap), and have the code cleared.
A lot of auto parts stores can do that for you free of charge.