Fuel gage reads empty all the time put on new sending unit that did not help

The sending unit on the fuel pump is bad. It sends a signal to the gage to tell the fuel level. The reason the mileage is moving is because the sending unit is miss reading the fuel level. The sending unit for the fuel level is in the fuel tank.

Most likely it is either the fuel level sending unit attached to the fuel pump or the stand alone unit (there are two sending units, both located in the tank), or, as counter-intuitive as it seems, it could be the speedometer assembly. Personally, I lean toward the latter.

generic sending unit? sending unit needs to be compatible with Isuzu's gage ohm-range requirements.

Only thing I can tell, with all you've checked, is the power to the gage isn't there. If the tank sending unit ground to frame is not connected, the gage will go past the full mark. No power to the gage it will stay at empty side. Power goes from fuse to gage, gage to sending unit and back to gage. Make sure the fuse is good on both sides of it. The gage just isn't getting power from the fuse.

One of two things: either the gage itself is malfuntioning or the float/sending unit in the gas tank is failing. Disconnect the plug at the tank for the sending unit, pick up a new sending unit and attach it to the plug without taking the old unit out of the tank. Then operate the float up and down on the new sending unit. If the gas gage reads correctly when the float is all the way up (full) and all the way down (empty) the old sending unit is probably bad and should be replaced. If there is no difference when you connect the new sending unit, the gage is probably bad. Then you can return the new sending unit (as long as the auto parts store allows returns of electrical parts) and buy a new gage. Install the new gage and...happy motoring.

Do you know if they also replaced the sending unit in the tank ?
It could also be a problem with the gauge on the dash.

Coulb be a bad fuel sending unit or a bad fuel gauge.

p0463 is a self diagnostic code that is for the fuel gage sending unit located inside the fuel tank if your fuel gage is reading empty just after you filled it then that verify's the code is correct you have a bad sending unit

Is......the problem--"the gas gage reads empty when there is fuel in the tank. OR, The gage moves when the key to turned off ?

If it's the first,
You will need to test the gage and through process of elimination, determin if the Sending unit inside the fuel tank has gone Bad.

If its the second ? - Electrical gauges will move when powered down. Normal

Testing the gauge may not be easy - just depends on your ability.
It is a simple 2-wire gauge circuit, when disconnect (usually need the fuel tank) the gage reads in one direction (either full or empty)
then when shorted-the gage reads in oppisite direction.

Of course you must select the correct wires or you may short out the wrong circuits!! Most GM vehicles use a purple wire & black wire.

A quick method I have used to check the in-take part of the gauge is this.
1st. know there is gas - 1/2 tank works best.
2nd driver's door open, key in run position, engine not running.
3rd gently lift up on the door then let if come back down, gently.
just enough to cause the gas to slosh around.
4th - keep an eye on the gas gage, a bad sending unit in the take will show up as a "twitchy" needle.

Of course, if the gage never leaves empty - sloshing won't work.
I have a known good sending unit I can plug into the vehicle and simulate different levels of fuel - if the gas gage works, I know the problem is in the tank.

Let us know.

Dave

sometimes beleive it or not its the gas cap is not sealing right