2005 Chevy trailblazer

It is likely the fuel sending unit in the tank. You can get that replaced at pretty much any repair facility. It shouldn't be very expensive, but I recommend letting a shop do it as you'll need to have a lift in order to pull the tank.

These models are notorious for the gage motors on the instrument cluster to go bad. To find out if it's the sending unit or gage disconnect the wires going to the sending unit (hopefully it's not that hard to get to) . When you disconnect it the gage should still read empty, jumper the disconnected end going to the gage then it should read full. If it does nothing more than likely it's a bad gage motor on the instrument cluster. Hope this helps

The sending unit is part of the fuel pump assembly. I just priced a fuel pump for mine and it costs $300 for a new one. The fuel pump is inside the fuel tank. That means the tank has to be removed from the vehicle to do the repair. It can take several hours to do the repair.

Well guys, I just replaced my fuel pump inn a 2004 trailblazer. As in you tube video's, it can be done on the ground, but you have to raise the front end, on ramps, and jack the back axle up. remove the left tire and spare if the cable unit still works, mine didn't. Then it is three bolts, wire connections and hose connection. Buy new plastic U clips, you'll break the one's in there. After that take a jack and lower the tank, replace the pump, and wa la, problems solved. Oh make sure you're tank is empty, makes it a lot easier to drop the tank down. Two or three people makes the job a lot easier. Also, if you take it to a garage, expect to spend several hundred dollars( likely close to $1,000 ) that will be for the pump and labor. I bought mine from rockauto for about 50.00. I also missed an electrical connection at the rear of the tank, another $50.00, so be very careful and check everything. The you tube's video's sometimes miss things, like that. Anyway, have fun and if you are 75, like me, it will take a day or three to get it done.