Car of year 1998, when tank is full or medium from fuel, guage shows empty. When tank is completely empty, the guage shows full. Guage is of digital type with the bars. What can I do ? Any tests I can do ? Where is the location of the sending unit ?

It sounds as if the fuel tank sending unit is faulty. This is a small float connected to a variable resistor on the fuel pump/sending unit assembly. Unfortunately this assembly is fairly expensive (over $300) and the fuel tank may need to be removed to replace it.

This problem is causes by a defective fuel level sending unit, The sending unit is located inside the gas tank and the gas tank must be removed from the car and the fuel pump module (contains level sensor) replaced to correct the problem. This job requires a hydraulic floor jack, safety stands to hold the car in the air safely and a very good set of common hand tools plus a special tool to remove the fuel lines from the tank. Time to complete is about 4 hours on the ground.

To confirm if the fault is with the Rheostat float within the fuel tank or the fuel guage in the dashbboard, you can remove the wiring to the fuel tank float. If the guage reading changes- to full- then the guage is good and the fault can be a jammed rheostat which can be removed from the tank and replaced after draining the tank. The guage can be tested on the outside with a ground wiring to the plate of the fittings and as the float is moved the guage must show a change in reading. if not the voltage must be measured to confirm the working of the guage.

Sounds as if the SENDING UNIT in the tank is faulty. They work by RESISTANCE, so when the contacts on the fuel guage sending unit in the tank get worn, it will send incorrect data. Typically it will say full when the actually IS full, then, when the tank is 3/4 full, it will say EMPTY, and then, as you use more fuel from the tank, the guage will go from what is REALLY in the tank, to empty, at different times.

Only solution is to remove the fuel tank, and replace the sending unit guage assembly.

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.

should be a grey wire going to the top of fuel tank connects to fuel guage / when the guage in the tank reads grounded it shows full , no ground it shows empty. if you ground that grey wire and the guage jumps to full then faulty guage if nothing maybe bad ground on the tank itself. the guages are a reostat like a tyco race car gun the more it moves the more it grounds .. good luck

Hi
We have the same truck that does the same thing.
The fuel sender in tank is faulty. It is in your gas tank. Common chevrolet problem.

Hello: Thanks for the follow up. Yes I did fix it. Somehow the needle had slipped over the rest pin
on the guage face, so it rested down in the bottom of the guage. When power was applied it came
up but was now stuck UNDER the rest pin at the EMPTY mark. I got a suitable piece of wire, and
manouvered it through the Odometer reset shaft hole, and carefully worked the needle back on TOP
of the rest pin......Problem solved. I have leared that this happens quite frequently to these Malibus.

Thanks again,
Bill.

REMEMBER>>Artificial intelligence is no match for natural stupidity.

Your needle moving from empty to full and then back to empty indicates that it is trying to set itself (most cars do this each time they are started). So, yes, there seems to be a problem with the sending unit that feeds information to your gas guage. Prior to cracking open your fuel tank, you might try tracking the wires from the back of your guage as far as you can towards the tank. Then track the wires from your tank as far as you can toward the guage. Watch for damaged wires and/or loose connections as you go.

This is not a calibration issue, the sender in the fuel tank is the problem, this is a common symtom for senders when they fail