Troubleshooting Your Chevy Truck Gas Gauge Failure

Jake Mayock

Meet Jake

Jake is a founder of 8020 Media and has been creating automotive content online since 2017. He has been the lead writer for Chevy Trucks and has transformed it from the old and outdated site it was into what it is today. Jake creates a ton of GM related content for the 8020 Media YouTube channel and specializes in Duramax and Vortec information but has a wealth of knowledge across all GM cars and engines. Jake believes the L5P is the best diesel on the market today.

Replacement Parts:
Tank Sending Unit
Sending Unit Float (only if not replacing the full unit)
Voltage Regulator

Most gas tank units consist of two parts, the gas gauge mounted in the dash and a tank sender mounted in the tank.

The following trouble-shooting instructions apply to the AC-type fuel gauge, which is one of the most common type of units. Your service manual will give you any added instructions necessary for your specific type of fuel gauge.

The gas gauge, often located in the instrument cluster, consists of two small coils spaced 90 degrees apart with an armature and a needle placed at the intersection of the two coils. A dampener is also located on the armature to prevent excessive needle movement on rough roads.

The tank sender unit is mounted to the outside of the gas tank (with a float on the inside, of course) and is made up of a metal housing that contains a rheostat (which is simply a resistance unit), and a brush that comes in contact with the resistance unit. The opposite end of brush unit is attached to the float arm located inside of the gas tank. The movement of the float arm is controlled by the amount of fuel in the gas tank. The variations in the amount of fuel in the tank cause the arm to move. This changes the resistance of the tank unit, changing the amount of current at the gauge unit coils, which in turn moves the needle located between the coils.

Beginning around 1950, some vehicles have a small voltage regulator behind the dash that supplies a stable voltage supply for the instruments – something less than the battery voltage of six (or 12) volts. This isolates the instruments from the effects of varying battery and generator voltage. So if you are checking voltage at the dash gauges on these cars and you read something less than battery voltage, it may be normal. Follow the power wires from the instruments and you’ll probably find the regulator.

The most common cause of gas gauge trouble is a poor ground, especially at the tank sender unit. It is important that all wiring connections are clean and tight, and free of dirt and corrosion. A poor ground or loose connection to a gas gauge is just as likely to cause problems as loose or dirty battery cables assuredly will with your starting system.

For example, if the gas gauge needle remains on empty when the ignition key is turned to the “on” position and you are sure the gas tank is partially full, battery current may not be reaching the gauge. To check further, connect a jumper wire between the ignition switch and the dash gauge. If the gauge now works, replace the defective wiring between the gauge and the ignition switch.

If the gauge needle remains stuck in one place, try turning the ignition switch off and on several times in succession. This will allow you to determine if it is the dash gauge or the tank sending unit that is defective. If turning the ignition switch off and on (a half-dozen times is a good test) does not seem to help, and you’ve verified that the dash gauge is receiving power, try the following troubleshooting steps:

A functioning sending unit will have a high resistance when the tank is full and a low resistance when the tank is empty. If the gauge reads higher than it should, make sure the wire attached to the electrical terminal on the tank sending unit is making a good ground connection. If necessary, clean the connection and reinstall the wire to the terminal, then check the gauge operation. If that didn’t fix the problem, use a jumper wire to ground the electrical terminal on the tank sending unit to the tank unit housing (leave the wire to the gauge connected to the tank unit). Turn the ignition switch on. If the gauge reads empty or below empty, the sending unit is defective.

If the gauge still reads high, try grounding the tank unit electrical terminal to a clean portion of the frame. If this brings the gauge to empty or below, the tank unit is OK, but there is a bad ground between the gas tank and the body or chassis (or less likely, between the tank unit and the gas tank). Either way, find and correct the bad connection or merely run a permanent jumper wire from the frame to one of the screws holding the tank sending unit to the tank.

If the gauge still reads incorrectly, the wire from the tank unit to the gauge may be faulty. Check by using a jumper wire to ground the tank unit terminal on the gauge (the one not connected to the ignition). If the gauge now reads empty or below, the problem is in the wire leading to the tank (or its connection to the gauge). If grounding the tank terminal still doesn’t cause the gauge reading to drop to empty or below, the gauge is faulty.

When the gauge reads lower than it should, check at the gauge by disconnecting the wiring from the tank unit. Turn the ignition on and if the needle reads full or above, the gauge unit is probably good and the tank unit or the wiring leading to it are probably the problem. Reconnect the tank unit wire to the gauge before proceeding.

The next trouble-shooting task begins by disconnecting the wire to the tank sending unit. If the gauge still reads full, there is likely a short to ground somewhere between the sending unit and the gauge. Look for worn insulation allowing the wire to contact the body or frame. If the gauge reads full or above with the wire disconnected, the problem is in the tank unit rather than the wiring. It could be an electrical fault, or the float may be stuck or may have sunk because of a hole caused by corrosion. Remove the tank sending unit and check it. If the float is bad, you’ll likely hear gas sloshing around in it or see gas dripping out. If the float is OK and the float arm seems to be swinging freely through its full range, replace the tank unit.

Ground the gas tank terminal post of the tank sending unit using a jumper wire. If the dash gauge now reeds empty, the gas tank unit is defective. If the dash gauge needle fails t move, the dash gauge is defective.

If the gas gauge works, but reads lower than it should, check for defective wiring between the gas gauge and the tank sending unit. Also check for a poor ground at dash gauge and the sending unit by using a jumper wire.

If the dash gauge reads empty when the tank is actually half full or greater, the wiring between the dash gauge and the tank sending unit is defective. Disconnect the wire at the gas tank sending unit terminal. If the gas gauge reads still reads empty, the dash gauge unit is defective.

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    Replace spider fuel injector and fuel pump 4 years ago,
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  2. well come to think of it I changed out the whole entire gauge cluster from another instrument panel and I barely got movement out of the other gauges awesome I changed out the lamps in the dash lights and I don’t know if it’s just a dimmer switch or what but Dad lights don’t Brighton nor do even dim and gas gauge full all time till bout 1/2. Tank and then its close to empty ideas

  3. In my GMC 2500 6.0 v8 the low fuel light no longer works and it runs out of gas with about 100-120 miles left on mileage range indicator. Gas gage still shows quarter of a tank left. Thoughts?

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  5. I have a 78 Chevy 1 ton dually that has sat for a few years. I got it back on the road and my gas gauge worked perfect for both gas tanks as usual then all of a sudden I started it up to leave and now my gas gauge is pegged as far as it can go above full and I have an 1/8 of a tank in one and a 1/2 a tank in the other tank but the gauge stays pegged on both tanks no matter what now.
    Does Anyone have any ideas what the problem could be ?

  6. I got a 92 chevy 3500 the gas gauge read full even when sending unit is unpluged from harness it has been changed over to a carburated 454 out of a motorhome and i think they pit engine and transmission from it in the truck how can i fix the fule gauge and i will have to do something with the speedometer too other than that every thing works

  7. I have a 2002 gmc diesel 3500 with dual tanks all of sudden while idle the tank reads empty when it’s three quarters full

  8. I have a 2006 chevy truck. The fuel gage is not working correctly. Was thanking it was the sender in the tank. Put the Mileage to empty is correct on my LED sup display So it is my gauge I’m assuming there’s an issue with thanks for any info

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