I think the problem I'm having with my '03 Bonneville may be kind of exclusive to GM vehicles. My problem is that when the fuel gage gets to a little less than 1/4 it starts to go nuts! It will slowly bounce between empty and full. Sometimes it will stop somewhere in between. At that point I have no idea how much gas I have left. If I fuel up with anywhere from 5 gallons to a fill up, then it works normally until it gets down to a quarter tank again. A friend with a '99 Tahoe has the same problem. What......is....going.... on here?
Anyone? Anyone?

the tahoe for sure has an updated sending unit (delphi fg0089 amazon has the best price) that has a different fuel sensor that doesnt bounce when it wears out. if you look at the old one you can see what happens. the connectors also go bad and it comes with that too. there is a ground you can see front of the driver wheel well that needs to be cleaned as well.

the bonnie not as sure about but still sounds like the sender, at certain places on the float sensor it maybe able to come apart and open= full tank on gms. so that being said an open in the connector on the tank or dash connector would do that too.

its more than likely the fuel sending unit. my car does this too, i generally go by the "fuel used" thing in the drivers info center. but if you do decide to change it, you need to pull the trunk carpet and there is a panel in the front passenger side of the trunk where you can take the fuel pump/sender assembly out without dropping the tank.

the part itself is about $40 on amazon.

here is a video tutorial.

with the amazon part, you dont need to jerry rig the part like this guy did, its premade. the rest of the video should be exactly what your going to have to do though.

I agree with Jason, it sounds like a faulty fuel sender. Pretty easy to change. If you do it, make sure you get a new O ring where the pump seals to the tank. Its about 3" in diameter.

Moved to 2000-2005 Bonneville Mechanical/Maintenance.

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I have seen alot about the senders on the Bonnevilles and other GM and non-GM cars reading erratic. I just wanted you to know a good solution to try before the sender change out.

I first worked at GM dealer in the 90'* when we were having sender and fuel injector warranty issues in GM cars. GM worked with Chevron to develop a fix for what they found on the senders as corrosion. Also the injector design had changed to a piped system and smaller injector spray nozzles that were getting plugged. Chevron had redesigned the Techron to help GM with these problems and installing the Techron was the first FIX under warranty per TSB, Technical Service Bulletins.


You can always try to run about 3 tanks of gas while using CHevron Techron in the tank. If you already use Chevron gas thats great but the bottle is alot mpre concentrated

Techron is the only real fuel additive that I have seen that works. It cleans up the corrosion that is causing the problem then coats the contacts to keep it from corroding again.

Techron really works and I have seen it. Worse case is that it does not fix your sender (might be too worn or corroded) but at least the injection system will be cleaner and probably run better.

" Techron to help GM with these problems and installing the Techron was the first FIX under warranty per TSB"

Interesting, thanks for posting the alternate fix. I am going to test this method today, will report back.

I have had pretty much the same problem with my 2000 Blazer. 1/2 to full tank and the gauge would behave normally. Anything less and it would go spastic. This is the cause right here. It'* the electrical contact fingers. They wear out. This is from either a 2000 or 2001 SSEi.




No amount of Techron is going to fix this.

Here is the link to the whole writeup.

https://www.gmforum.com/mechanical-134/fix-your-gas-gauge-broken-step-step-guide-289937/

thats the same as was in my yukon, those things wear out and so do the bushings so the float arm can pull away from the resistor part causing sporadic opens. delphi had an updated design that even as it wears cant separate like that. also has a few other updates for new harness that is less likely to loosen.

I have installed the updated DELPHI fuel pump in my Bravada and S10- the cause of failing was often identified as a connector that was to small to allow full current, causing premature failure of components. On a Blazer/ Bravada/ S10 replacement of the fuel pump is mandatory as a preventative measure, the OEM pump will prematurely fail. That is not the case with the Bonneville fuel pump.

On the Bonny, the fuel pumps seem much more reliable, and I was hoping the sensing failure was a different issue than the fuel pump and/or sensing failure of the Blazer/Bravada etc.