04 TB, fuel gauge not working.

mbrugh

Original poster
Member
Mar 26, 2013
7
I have a 2004 TB with fuel gauge reading empty. I removed the dash cluster and had it completely rebuilt with all stepper motors. The board was cleaned. Fuel gauge still reads empty. Next replace fuel pump assembly and before I installed pump into the tank, I plugged sending unit into to harness to check operation and the gauge reads the opposite of what it should read. When the float is down it reads full and as I raise the float up it move towards empty. The pump turns on for about two seconds and cuts off. Is there a ground issue? All the wires appear to be connected correctly. Any help please.
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
If you turn the ignition on without starting the engine, the fuel pump just gets a short blip like that to pressurize the fuel lines. I'm guessing here, since I don't recall anybody ever doing that test with the pump in mid-air. But if the pump runs at all, I wouldn't suspect the ground.

Also never read about a reversed sender unit. Do you have a voltmeter and want to trace the voltages in the harness? If you hadn't already worked on the gauge cluster, I would have recommended using a scan tool that can read data (usually $100-150 sort of units, not the $50 cheapies) to read the sensor data to confirm it was the gauge versus the flakier sending unit.
 

CaptainXL

Member
Dec 4, 2011
2,445
mbrugh said:
All the wires appear to be connected correctly. Any help please.

I think you got an incorrectly wired sending unit/pump. You can check from the harness to the gauge with schematics, a little electrical skill and a few resistors. If that checks out I recommend you take it back and get an Airtex unit. Or just reverse the wiring at the sending unit.
 

mbrugh

Original poster
Member
Mar 26, 2013
7
the roadie said:
If you turn the ignition on without starting the engine, the fuel pump just gets a short blip like that to pressurize the fuel lines. I'm guessing here, since I don't recall anybody ever doing that test with the pump in mid-air. But if the pump runs at all, I wouldn't suspect the ground.

Also never read about a reversed sender unit. Do you have a voltmeter and want to trace the voltages in the harness? If you hadn't already worked on the gauge cluster, I would have recommended using a scan tool that can read data (usually $100-150 sort of units, not the $50 cheapies) to read the sensor data to confirm it was the gauge versus the flakier sending unit.

I did check the pump for the 2 sec operation and it did cycle. I checked the wiring with Gm wiring diagram and its correct. I installed the pump and sending unit and it works but the tank gauge reads empty when its full. The gauge cycles through when I first turn the ignition on as other TB that I have compared too. It just works opposite for some odd reason. I been told to use a tech 2 scanner to check the system for errors. I been told that the PCM controls the instrument cluster. I also been told that my system may need to be flashed. If thats what it needs I am ok with that. I have installed many fuel pumps and never had this happen. Oh I forgot to mention that after I checked out 2 pump asmy, they all did the same operation. Even the OEM AC Delco. It also was a direct plug in fit on the harnest.
I am confused on this one.
 

mbrugh

Original poster
Member
Mar 26, 2013
7
CaptainXL said:
I think you got an incorrectly wired sending unit/pump. You can check from the harness to the gauge with schematics, a little electrical skill and a few resistors. If that checks out I recommend you take it back and get an Airtex unit. Or just reverse the wiring at the sending unit.

I checked the wiring schematics and all the wiring matches up. I also switched the two wires that lead to the gauge and it did nothing at all, no movement in y
the gauge at all. I installed the new pump asmy and the pump work as it should but the fuel gauge reads the opposite. I never seen this before and I have installed many fuel pump units. I been told that I may have to have my TB system re flashed by the dealer.
 

christo829

Member
Dec 7, 2011
499
Fairfax, Virginia
You might also pull the instrument panel and make sure the correct stepper motor was installed when it was rebuilt.
Not only is it possible to get a bad one off the shelf, some have the same form factor but are internally different, so
make sure the motor part numbers are the same. Check to make sure it was installed correctly, needle was pushed
back to the stop, etc.

Do you get the calibration "twitch" from the gauge when you initially start up (nevermind...read that you do). Does the "Low fuel" light come on?
I'd be more likely to suspect wiring/circuit problem before PCM. I don't have the wiring diagram in front of me, but
I think the low fuel light gets triggered from the PCM. If it doesn't come on, the PCM thinks you *have* fuel, so the
gauge and circuit to the pump assembly is more likely where the problem still exists.

The sender is pretty much just a variable resistor, not directional, so it's not polarized. I'm assuming you checked the
signal from the sender?

Know anyone that you can swap instrument panels with temporarily?

Good Luck!

Chris
 

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