by "bwp240" (bwp240)
Published 03/13/2017 at 12:10
by "bwp240" (bwp240)
Published 03/13/2017 at 12:10
Tags: The joys of high mileage car ownership
STARS: 0
Greetings Opponauts, particularly those with more automotive electronics experience. I have a mullings over, and I want to get some input from people smarter on cars than myself. My gf has a 03 Buick Century and recently the fuel gauge failed.
Upon starting the car the gauge pegs at ‘Full” then after about 30 secs or so it dies and goes to “Empty.” It is worth noting that the car had about 1/2 a tank during these tests.
The fuel pump was recently replaced and it lasted about 2 months before this failure. Thinking it may be a faulty part we (my gfs dad and I) replaced the fuel pump under warranty (yay no money), but the problem persists.
We then examined the gauge cluster to see if that was the point of failure. Checked and found continuity between all the points, but no resistance between the ground and fuel pump circuit (forget the technical name). However, I do not think it is the line back to the pump because it would not be getting any signal at all.
The circuit diagram shows an analog signal from the pump, going through the PCM which is converted to digital, then converted back to analog on the logic board for the fuel gauge. All electronic nonsense to me (her dad is an house electrician - so he sort of understands this stuff).
He is thinking that it may be something with the cluster circuit board itself. The main skepticism with that is the fuel gauge is the only faulty gauge. I would think if it were the board, many gauges would fail.
I conducted some research and consulted with friends and the stepper motor seems to be a common failure point. The Buick LaSabre was noted as a unofficial addition to the GM Cluster Recall of 2008. The 03 Century looks to use the same board and similar parts as the LaSabre so I could see it also being affected.
However, there are two more points of interest. The gas light comes on when the gauge fails and chimes. I am fairly certain that the light is tied in with the gauge position, but I know on some GM’s it is not, and could be an indicator of something more serious. Also after the gauge failed a CEL came on with a P0452.
So the gauge failure plus the CEL makes me a bit confused about it being simply the gauge motor. [I should note that we forgot to reset the CEL after changing the pump.]
Anyone out there have any suggestions? I am trying to avoid having to replace the cluster/board and reprogram the mileage (don’t want to do all those state forms and such). I also hope we are not rewiring the entire fuel system. I would much rather do 1 or those three things instead of all 3 of them.
I appreciate any input. Thanks.
"itschrome" (itschrome)
03/13/2017 at 12:21, STARS: 0
these cars have an issue with bad dashboard circuits that cause gages and dash lights to stop working. they used some cheap shit resistors that can fail and need replacing. I had a fairly steady supply of work from these back in the mid aught’s and early teens been a while since i’ve encountered on. not saying this is your issue more of an fyi.
"bwp240" (bwp240)
03/13/2017 at 12:32, STARS: 0
I should have stated that the dashboard resistors were already replaced
"itschrome" (itschrome)
03/13/2017 at 12:38, STARS: 0
oh ok, then I’m of no use to you. Good luck!
"The Stig's former college room mate" (das-stig)
03/13/2017 at 17:01, STARS: 0
I found the sending unit to be the most likely culprit on older GM’s like this. I used to keep a known-good sender out of a fuel pump module i had replaced so i could test them.
"bwp240" (bwp240)
03/13/2017 at 17:25, STARS: 0
we tested the old fuel pump and the sending unit tested fine (saw changing but unwavering resistance when moving the float). The brand new one we didn’t test before putting in, but it is a new Delphi part. So I don’t think it is the issue.
I am really hoping it is not something between the pump to PCM, or PCM to dash. I really only want to do that if we are certain that is the issue.
"The Stig's former college room mate" (das-stig)
03/14/2017 at 11:18, STARS: 0
if you still have the old part you could plug it in and test it easy enough. It wouldn’t be the first time I saw a bad sender right out of the box.
But since you also now have a fuel tank pressure sensor fault, you may have a damaged harness. could it have gotten caught when you put the tank back in?
"bwp240" (bwp240)
03/14/2017 at 12:20, STARS: 0
Thankfully on this car the fuel pump is not secured to the inside of the tank so we didn’t have to drop it out. It has a little access in the trunk. The CEL came on before the pump was replaced and the old pump worked fine. It very well could be the harness, but I am not certain. I think the harness is part of the pump so that should in theory be replaced.
Her dad is making the decisions on what to fix next because it is his car. He is planning on getting the sending unit circuit tested so we will know if it is something from the pump to the dash circuit board. Other than that, I am in the dark to what is being done next.
I am leaning toward doing the steppers, because it sounds like a pain to get the odometer corrected and certified (there are two or three state forms we need to fill out). If that fixes it then we are done. Just thinking about the easy stuff first.
"The Stig's former college room mate" (das-stig)
03/15/2017 at 11:45, STARS: 0
Back when I was a GM tech, there were many vehicles that had TSB’s recommending replacing the (vehicle side) harness when changing the fuel pump module.
Oh, and GM digital odometers store the mileage in the body control module, not the instrument cluster. So if you swap clusters, the odometer should read correctly.