hi i have a 05' pacifica and the fuel guage would flucuate from 3/4 tank to full after a fill up. i took it to the dealer and 3 days later they told me it was the sending units. so we replaced them. when i got it back it was still doing the same thing. we would fill the tank full, drive it for 68 miles, the gauge would read 3/4 tank. if you let it idle with the a/c on within 5 min the guage would climb back up to almost full tank. if you turned the car off and back on the fuel guage would go back to 3/4, but after idleing for 5 min with a/c on the guage will climb back up to almost full. once you start driving it the guage slowly goes back to 3/4. i have had it back in the dealer 3 times since, but all they have done is reprogrammed the bcm and it still does it. it didn't act like this when i first got it. i should be getting more than 68mi between full and 3/4 right? on the highway i can get 140mi is this right? do i need to replace the cluster or the sending units again? the dealer is helpless.
thanks adrian

 

Sounds like you may be a little uncertain about the gauge accuracy, meaning a 1/4 tank in 68 miles. You can get the fuel tank capacity, average mpg, and divide just to confirm.

Regardless, it should not vary from full, 3/4, and back again.

The sending units supply a variable ground circuit to the BCM. The BCM translates and sends a signal to the instrument panel. A problem could be in the panel, the BCM, and any of the circuits in between. And of course a software issue is always a possibility, but there are no relevant technical service bulletins and they've already reprogrammed with the latest.

Before replacing any more parts, go back to the dealer and politely ask them to locate and check the ground for the senders, and continuity from there to the BCM.

Nothing there? Then they can start swapping parts.

But be nice to them. Trust me, a bad attitude will makes things worse, and the guy working on a warranty problem like this is losing money.

 

i have checked the grounds and they are fine. could it be that the fuel modules and siphon house are going bad? i ran this idea by the dealer and they said it might be. does anyone argee with this? ive read another post where they replaced them all and problem went away.