2005 Chevy Malibu gas cap tightened, chk eng still on.

Hard to say. The gas cap might have been loose. That will turn the Chk Eng light on. When you filled the gas tank you made the cap tight again.

Get the codes read again if the light comes on again.

did you try to reset.

if you have auto daytime lights and they don't work then your radio will not work either. trust me on that. you have one lead to 12v source and acc lead that is wired to auto daytime lights which when you open your door radio shuts off.

not sure how that could be the cause, but check to see if vent valve is stuck closed. Otherwise, see my notes at link below.
Do It Yourself Diagnosis and Repair

Could be any number of problems
Take the car to AutoZone nd ask them to check the computer code. They will do it for free and give you an idea of what may be wrong.

Did you recently get gas? If the gas cap is not put back on and tightened it will set the the light.

hey the reason your gas gauge is going from full to empty is that your fuel pump which is in the gas tank has a sensor that relays how much gas the tank has in it, the sensor is gone bad and will have to be replaced. And your engine light problem is probley due to putting gas in the car while it is running, my wife has a 2005 malibu and we have had the same problems with her car hope this was helpful

I had check engine light and TRAC OFF. OBD-II MIL code was P1133 which is Air Fuel Ratio Sensor Response Malfunction and scanned by AutoZone. After disconnecting the battery for 10-15 minutes, the lights went off. I cleaned the gas cap and tightened it firmly. For the last 400 miles, the lights have not come back. When scanning using Snap-on one, no code was detected. I think gas cap was the reason for the lights.

There is a couple ways to do this, either clear it with a scanner(if you own one) or disconnect the battery negative side of terminal and wait thirty seconds then reattach.Be sure to write down your radio code just in case if you still have the stock radio and it has theftlock...HOPE I HELPED!!!

This could be a number of things causing this ...most common is that after you fill up the gas cap is not fully tightened...make sure it "clicks" 3 times while turning.The other common problem is that the gasket on the gas cap is old and thus does not seal the tank/fuel filler area...check with replacing the cap.If neither correct then you will need to bring to a service center or dealer to run a code check...maybe a bad O2 sensor or a code for the transmission.

I doubt the gas cap is related to the light, though hopefully you can get a replacement for it because it can be dangerous. As for the check engine light I'm not sure what it could be. Is the car running making noises, does it stall?? If there are no obvious symptoms, you might need to take it to a mechanic so they can read the error message from the cars computer and determine where th eproblem is.