Erratic gas gauge/electrical issue?

Hey guys, I ran a search and saw multiple responses related to the sending unit needing replaced for an erratic gas gauge on a 2003 Pontiac Grand Prix GT 3800 series engine, but is it possible that the issue is electrical? Or is there a way to check? I don't want to spend all day replacing the sending unit on the fuel pump just to find out that wasn't the problem to start with (one person said it took 30 minutes and another guy said he spent 6 hours).

My local shop is telling me the problem could be caused by something other then the sending unit. Also, if it is the sending unit they want to drop my gas tank to replace it even though I have an access panel in my trunk behind my back seats (they said they have never used an access panel and it would take just as long for one of their guys to figure it out that way as it would to drop the tank since that is the way they know how to do it). They did offer to do a diagnostic for $90 to figure out what it is before they do anything else, but I'm hoping to save the $90!

I do not have a check engine light on, the car starts fine, it runs fine as well. For now I am just keeping track of my miles driven between fill ups. :dunno:

Any advice and help is appreciated! Thanks.

Dropping the tank on your car to change the fuel pump sending unit is like pulling the engine to change the oil. It's obvious that this shop is either not very smart, or they want to soak you for the extra labor to drop the tank. The rear seat back has a total of 4 bolts holding it in (the lower cushion has two pull tabs at the front that unlock it), and the cover in the trunk has 7 nuts that hold it down. REmove the seat and covev, and the fuel module is right there. You'll need a brass or wood dowel to tap the lock ring out (you don't want to create sparks around an open container of volitile liquid) and the 2 fuel lines and vapor hose have squeeze release clips. I did the fuel level sensor on my mom's Monte Carlo (very similar to the Grand Prix) in less than an hour. If I had to do it again, I could do it in about half that, as it took me a while to figure out how to get the back seat out (hers is different than my Grand Prix). As far as testing, the fuel module harness has 4 pins, two power the pump, the other are for the guage. The guage is essentially an ohm meter, and the level sensor is a varying resistor (range is 50-250 ohms or somewhere close to that). These are a fairly common issue on GM cars, and is most likely your problem.

To add what Rich stated, I just changed out my whole pump/sending unit assembly and was very easy to access the pump by just folding down the rear seat armrest and opening the pass threw door (if you car has one). Then peel back the carped.

If you need a new sending unit. I have one out of a 2000 GTP that works 100%. Just the fuel pump is bad. You would have to swap in your current pump into my sending unit and put it back in your car.

Send me a PM if you interested in my sending unit.