Rear fuel pump not working on my '02?

[John_McFly]

So the gas gauge on my '02 Yukon XL 2500 6.0L has been acting a bit funky lately, once I get below ~9/16 of a tank the needle starts to drop like a rock. The last time I went below 1/2 tank it went from ~7/16 of a tank to ~1/4 of a tank in <15 miles, when I hit the gas station it only took on 22 gallons of fuel instead of the expected 30 gallons.

 

I looked all over the left rear frame rail for the rear pump relay and connection to see if I could test the resistance of the pump or jumper it to see if I could get it to cycle, but I couldn't find the connection or the relay. Am I looking in the right spot, or does anyone have a picture of what it should look like?

 

Both my work's scan tool and the mechanic's only read the gas gauge's reading from the dash, they can't seem to pull individual tank values, is that only available on later vehicles?

 

Is there any other way to test it other than bring along a bunch of gas cans and drive it until it stalls?

[slj2008]

So the gas gauge on my '02 Yukon XL 2500 6.0L has been acting a bit funky lately, once I get below ~9/16 of a tank the needle starts to drop like a rock. The last time I went below 1/2 tank it went from ~7/16 of a tank to ~1/4 of a tank in <15 miles, when I hit the gas station it only took on 22 gallons of fuel instead of the expected 30 gallons.

 

I looked all over the left rear frame rail for the rear pump relay and connection to see if I could test the resistance of the pump or jumper it to see if I could get it to cycle, but I couldn't find the connection or the relay. Am I looking in the right spot, or does anyone have a picture of what it should look like?

 

Both my work's scan tool and the mechanic's only read the gas gauge's reading from the dash, they can't seem to pull individual tank values, is that only available on later vehicles?

 

Is there any other way to test it other than bring along a bunch of gas cans and drive it until it stalls?

 

I think the only connection is on top of tank ( fuel pump/filter in tank ) old age ???????

[John_McFly]

My understanding of the wiring is the relay under the hood powers the front pump and provides power to a second relay (located towards the rear of the vehicle) controlled by the computer. The rear pump should have a relay somewhere since the computer can't provide enough power to make the pump run.

[Formulabruce]

Simplest thing first. Get a new stepper motor in the dash, They are cheap and much easier than fooling with the rest. Fill your tank up, get new motor installed ( or do it yourself if you can solder and de solder) and then sync it to full with key on, and give it a try. this is a common problem with the gauge motors

[John_McFly]

If the stepper was bad, wouldn't I see a difference between the scan tool's output and the gauge? The gauge appeared to move to the proper positions when I commanded them (0, 100, etc).

[Formulabruce]

If the stepper was bad, wouldn't I see a difference between the scan tool's output and the gauge? The gauge appeared to move to the proper positions when I commanded them (0, 100, etc).

If your motor has never been updated, its the cheapest and easiest thing to try first . When they mess up, they dont always mess up