fuel gauge not workinng on 2005 GMC Envoy

About 4 months ago my fuel gauge quit working. I had fuel sensor and pump(for good measure) replaced. Now the gauge quit workinmg again, but this time it sits pointing straight down - is it the dashboard gauge? Also, check engine light has been on lately.

Asked by for the 2005 GMC Envoy
Start with the code for the Check Engine Light just to eliminate that as a possibility. A good way to check a gauge is with a gauge sweep tester. See if you can borrow one from a parts store.
As a Pro, I would read the instrument cluster data stream and see if that agrees with the fuel level sensor reading. Then I know and don't have to guess.
2 answers
My 2006 Envoy had the same problem. Before you go to GM dealer for $400 repair, check and re-ground fuel system wiring harness. On the driver's side frame, just below pasenger door, there is a ground lug bolted to the frame. Remove it and sand down both the lug and frame around the hole. If you can, put a internal-external tooth lock washer between the car and lug. After tightening it down, apply silicone grease over it. Check to see if it fixes the problem. I was into replacing the sensor by dropping the tank when I found the connection, and it was very rusty. here is a link to a source for that washer-