I've got an 04 Bonneville SE. The gas gauge has been all over the place for over a year now. I had been going by the trip oddometer, until I ran out of gas on the way to work one day with only 46mi on it. So one of the kids must have hit the damn button. Money has been tight so my father ordered the part for me as per the Tech Info article on said problem. I replaced the little wiper as instructed. The old one was worn down alot. Anyway I filled it up and the needle kinda jerked a bit and stopped at 5/8 tank when it should read full. I tore it apart again (this time on a full tank so it was a lot messier) and checked the movement of the float. Everything seemed to be moving fine. The other thing I noticed was that it stays at 5/8 of a tank- even when the car is off. I don't recall, but I know all the other gauges zero out, max out, then go to where they need to be when you go to start the car. I assume the gas gauge should be doing the same thing? Please let me know and any ideas would be great. Thanks

To check the sensor, pull the pump and check resistance across the two wires as you move the float arm all the way from one end of travel to the other. I am not sure which end of the travel has high resistance and which has low, but you will know right away. You are lookihg for a steady change from high to low, or from low to high as you cycle the arm. If it gets to the 5/8 point and the resistance does not change from there up, the sender is defective.

The only other thing I can think of is the pump is slightly out of position, and the float is hitting something. Try seeing if there is any play in the location and see if you can't change the position relative to the tank. Try a couple of positions if there is a large range of motion. That will be easier than pulling the pump.

Let us know if this helps. https://www.gmforum.com/t281507/