ENVOY FUEL GUAGE PROBLEMS--- GAS GAUGE DOES NOT REGISTER ON FILL UP--- CHECK ENGINE LIGHT COMES ON WHEN YOU FILL UP -----THEN GOES OUT AFTER 1ST. 20 TO 40 MILES. BEN GOING ON FOR LONG TIME ONLY WORRY WHEN ENGINE LIGHT COMES ON

It is most likely your fuel level sending unit has gone bad. It sits inside your fuel tank to tell the fuel guage how much gas you have in the tank.

The sending unit for the gas gauge is in the fuel tank and part of the fuel pump module, it is not sold seperately. Price is around $350.00, 2 hours labor to install the part.

You can just replace the gas cap...However about the fuel guage fluctuates back and forth...thats due to the sending unit, which is located on the fuel pump itself

This is a safety feature that the vehicle brings. You need to reset the E.C.U on dealership or it will keep doing it to you. It was probably caused by one single time that you did not closed the fuel cap correctly. Good luck

GM had a problem with the fuel sending unit cards inside the fuel tank,If you replace that you should be good to go.

Also, be sure to not over-fill the gas tank. When filling the tank, when it sounds full (you can hear gas gush up the filler neck) and when the filler clicks off the first time...don't be tempted to keep clicking more gas into the tank because over-filling can cause a variety of problems (including setting the light) and can eventually saturate/ruin the fuel vapor canisters.

Common problem on the 03-06 Envoy instrument clusters for the fuel gauge to go out. It's usually caused by one of two main problems, either the stepper motor on the cluster's circuit board is going out or the sending unit on the fuel pump is going out. Check out this blog post about the problem - Envoy fuel gauge problems

The sending unit in your tank is bad replace it.

this is caused by one thing only, the gas guage sending unit is defective, this fuel gauge sending unit is part of the gas tank mounted fuel pump module, cost $360.00. see photo.

Sending unit. Its all one unit including fuel pump, float, ect. The check engine light is because of the high or low resistance in the unit. Let me know if you have already fixed.. You have to drop the tank to get to it also.

Mine did this too... Bought a new fuel sensor for 50 bucks and it's perfect now... if you don't want to spend the cash take your tank off take out you gage and check the floater and all the connections... could have just gummed up or disconnected