2002, 2500 Chevy Diesel guage reads empty when not, new sending unit in forunt tank.

Check the supply voltage and connectoins between the guage and tank sender.

The problem you explain usually has something to do with the sending unit float. Floats can absorb gas to the point where they just sink to the bottom of the tank. This can happen with both brass and plastic floats. The second thing is the sending unit you installed in your tank. Check to see if when you placed the unit in the tank , the float arm may have hung up on a baffle or some other obstruction in the tank. This would keep the sending unit from showing correctly. Good Luck Friend.

Sending unit is inside the tank. First, check that if you ground the signal wire near the tank then the gauge rises. If so, you must pull the unit from the tank.

check the sending wire to see if you have a bare spot
if you don't know where the sending wire is we don't know either
as what year
model
etc

sounds like you need to change sending unit in the gas tank

David Johnson is wrong about that. The Chevy HD dual tank has two sending units, one in each tank , one fuel pump, a fuel pump relay switch and a equalizing pump. If the truck stalls out at 1/2 tank, it is the equalizing pump. That pump, pumps fuel from the rear tank to the front. If the pump is out, the front tank empties, the truck shuts down, the guage reads half tank because the back tank is still full, but the equalizing pump won't pump the rear fuel tank load to the front. Hence the problem you listed above, not a sending unit.

Thanks for choosing FixYa and welcome. You may have a bad sending unit. It could also be a defective dash voltage regulator, lost ground at sending unit, break in the wire at the dash harness too. It can be anyone of these to be honest.

A loose connection on the sending unit could cause the problem but also moisture in the tank in cold weather could also be a factor in which i would add fuel line antifreeze to a full tank of fuel..........Hope this helps you out.

If gas guage is pegged either full or empty, it is most likely a broken wire to sending unit on the top of the tank. If guage reads wrong, like too much or too little is either bad sending unit in tank or bad guage in dash.

Your sending unit inside of the fuel tank is probably faulty. Unfortunately you have to drop the tank to change it.