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2003 Impala Gas Gauge

I have a 2003 Impala with about 122,000 miles on it. On my recent fill up I by accident put in mid grade over the normal unleaded, now I now that won’t cause any engine issues that I am aware of, but after doing this fill up my gas gauge is not working properly. When I start the car in the morning the gauge will go to where it should given the milage I have driven to this point but as I drive the car the gauge goes up to almost full then down some but never back to where it should be. what might be causing this floating incorrect reading by my gas gauge.

The grade of gas will not affect your gas gauge. Overfilling the tank might have an effect. Do you stop at the first click when gassing up? If not, you may be causing problems with the vapor recovery system which could affect the gas gauge.

A cheap first step would be to change the gas cap and make sure it’s on tight.

You will likely need a skilled mechanic to sort this out.

Well my thought process is if it’s just a gas guage issue I won’t be fixing it anytime soon, as it’s not a big deal as I monitor my miles driven pretty close and well know what I need gas.

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My late mother in law had a 1994 Pontiac Sunbird which she sold at age 92 with only 45,000 miles on it. The only thing wrong was a non functioning gas gauge.

The girl who bought the car never bothered to fix it; she just eyeballed her consumption by reading the miles driven!

I don’t think it’s a gage issue. I think it’s a “sender” issue. The gage responds to a signal sent from a float that’s part of the pump assembly. I think the float is hanging up.

But I’d also like to know the answer to Doc’s question. Do you “top off”{ when you fill up?

I concur that it is probably a sender issue. GM had some problems in certain cars in this time period. I had this exact problem on my 2006 Chevrolet Uplander. Fortunately, it was still under warranty when the problem occurred.

Yep I am guilty of being a Topper, I aways try to seem to get as much gas in the tank as possible.

Yep I am guilty of being a Topper – Well stop doing that before you cost yourself evap repair if it is not to late.

I have been doing all my life and never had an issue, didn’t know it was an issue.

My 2004 GM truck has had all kinds of silly gas gauge issues. Usually caused when the transition occurs between summer and winter gas in the fall. It apparently creates deposits on the sender giving bad readings. A work colleague was actually assigned to fix the problem when he was at working at Delphi and never was able to fix it.

My gas gauge would show inappropriately low fuel levels. It took a bottle of Techron fuel injector cleaner in a tank of gas to fix it until the next fall. Techron worked the best for some reason. Give it a try, couldn’t hurt.


I believe @Mountainbike & @Triedaq have this figured out for you.

I’ve been there, done that on an Impala of the same era as yours. The gauge went funky, caused by a bad fuel gauge sensor (sender) in the gas tank. it’s quite likely the same issue with this Impala, too.

There are very fine little wires on the wiper part of the sensor that “dissolve” due to something in the gas. That was the case with mine when I examined it. I’ve heard people blame sulfur. I’m guessing GM has since changed the composition of the metal of the wipers to revise the sensors.

I replaced the (sender) out in my driveway and the problem was solved. Replacing a gas tank sensor is usually pretty labor intensive because the gas tank needs to be removed or lowered, but not so on these Impalas, fortunately!

Under the trunk carpet on the floor of the trunk near the back seat, on the passenger side is a small oval access plate with 6 or 7 small fasteners holding it in place. The fuel pump module (with sensor attached) can be withdrawn through it.

Repair shops will tell you need an expensive new fuel pump module or complete sending unit and charge to remove the gas tank, but oh, not true! I found a You Tube video showing how to order an inexpensive GM sensor (made for another model under warranty replacement like the one Tridaq referred to), an exact fit part and remove and replace only the sensor wiper!

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It became an issue when car started to be equipped with vapor recovery systems. Our 1976 Ford Granada was the first one we owned, but that system did not send signals on the dashboard.

Later models did. When the vapor recovery filter gets full of raw gas you will have lights flashing and the fix is about $500 for a new vapor canister.

Is repair needed? I mean not having a working gas guage is a pain, but it won’t cause any other harm to my car would it/

No! You just won’t have a working gas gauge.

Try a bottle of Techron in the tank.
Sometimes that works.
worked for me.
Set off for Albuquerque for a doctor visit. 140 miles one way with the Miles To Empty showing 210 mte.
In Albuquerque the mte showed 180 .
do the math.
Since I planned on filling up to go home I clearly knew my next step . . hunted out an Auto Zone ( a pretty simple task in Abq. ) and threw in that bottle of Techron .

    • perfect ever since.
      now , once a year or so , I dump in a bottle just for giggles.

I’ll tell you, this fix is pretty easy on the 2000-2005 Impala compared with most other cars! Mine was easy and cheap DIY. I’m glad I decided to fix it instead of tolerate it. These are great cars and worth maintaining. Start letting things go and soon you’ll be driving a heap.

I’d search for the video I talked about, buy the cheap genuine GM sensor, and find a local mechanic to make it right at a reasonable cost (an hour labor?).

@common_sense_answer. This is interesting. My problem on the Uplander started after I started buying my gas at a different station.

As regards “topping off”, I recommend you discontinue this practice. Release of hydrocarbon molecuules (gasoline vapors) into the air was banned by the EPA decades ago, but gas tanks have to be able to purge their tanks of the gasoline-saturated air in the tank when filled and when the gas is agitated during normal driving (agitated fluids take up more space). To allow this, manufacturers created s system for the tank to breath out through an “activated” charcoal bed (activated charcoal is acid-washed to make it pouorus, dramatically increasing its surface area). The hydrocarbon molecules stick to the charcoal (carbon bonds well to carbon) and the other components of the air (nitrogen, oxygen, and about 1% argon and misc) pass through freely. When you start your engine, the hydrocarbon fumes are drawn into your engine via the “purge valve”. The tank also breaths in through the charcoal bed. In some cars, topping off the tank can allow fluid gasoline to get into and saturate the charcoal bed, preventing the tank from breathing. This can cause premature fuel pump failure, as it struggles against the vacuum that develops in the now-unable-to-breath fuel tank.

As regards the sulpher, there was a class-action lawsuit filed (that resulted I believe in a settlement… if I remember correctly) in about 2004 for massive amounts of sulpher-rich gasoline that was distributed throughout the southeast U.S. The sulpher was forming sulpheric acid and corroding the fuel pump electrical connections. Sulpher levels are now kept low by regulation, and I’ve not heard of a repeat of the problem.

I struggle putting gas in my car, I am not a DIY for anything car related, I would end up either in the hospital or having to buy a new car, if it bothers me enough down the road I will have a professional take care of it.

You’ve probably already saturated the charcoal bed.
I’d NOT top it off anymore and hope the charcoal dries by itself (via the purge system) and the symptoms disappear.
Meanwhile, if you begin losing power going up hills and/or accelerating, especially if it get severe enough to cause stalling, keep the charcoal bed in mind. You may end up replacing both the fuel pump AND the charcoal canister. Consider it the cost of an education.