Erratic fuel gauge : bad float/sender or stepper motor?


Active Member
Not sure which the cause of an issue is more likely the case, so figured to check here and then ask for opinions..

2004 Envoy XL
175k on odometer
Recommended service done since 36k
Drive 80 miles round trip each day for work mostly highway

Few weeks ago I noticed the gas gauge was not moving below 1/4 even when park on hills. Good thing I always reset the trip as some quick math told me I was low. So I stopped for gas and sure enough she took 23.5 gals.

Gauge seemed to work / reset normally when I start the truck as in it would go from far left when off, to full right, to rest at half tank. A few days like this not going below 1/4, then I noticed while driving, the needle slowly went all the way to empty, then all the way to full.

It stayed that way for a few days. Then I noticed a few days ago it would slowly move between full and 3/4. It is back to staying at full. Yet this entire time it still does the normal full sweep when I start the truck?

So .. Bad float / sender unit or bad gauge temper motor?. (on a side note .. The dash light that illuminates the right half of the speedometer is out)

Any thoughts would be appriciated


Founding Member
Probably not a bad stepper, but a decent scan tool or if you have an Android phone, the Torque app, can look at the sensor data and see what the truth is. Whenever you have two competing theories, you need a third data point to break the tie.


Active Member
Thread Starter
Thanks for the reply Roadie .. gives me something to consider .. like buying a new scan tool :smile:


Active Member
Seconding the sender diagnosis. When my stepper motors flaked, they failed to do the calibration step properly at startup.

Good Luck!


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