GMC TWO GAS TANKS WHY NO SELECTOR SWITCH. HOWS IT WORK?

My 02 GMC 3500 Dump fuel gauge is broken. The gas gauge shows E and the fuel message board says low fuel. It has two gas tanks but no selector switch, and it seems to pull gas from both sending units at the same time, while keeping track of the total fuel amount. I tried installing a new sending unit in each tank, but that didn't solve the issue. Does anyone know how this system works--or know how to repair this problem
Thanks for any help you might be able to offer.

Trucks of that "era" had a problem with the gauge cluster that would make the fuel gauge (and/or other gauges) not work.

Quick google search says that onboard computer monitors the fuel level in both tanks and averages the fuel remaining to show on your gauge.

The primary fuel pump is in the front tank. When the level in the front tank drops, it sends a signal via a fuel pump relay to trigger the rear fuel pump to send fuel to the front tank.

And supposedly the only way to really get into the diagnostics is with a newer model full blown scan tool. Generic OBD II readers don't work.



Hope this helps.


Probably is it was me, I'd try to do away with the automatic crap and put in manual activated switches and pumps.


Rick

Excellence in the electrical engineering dept of GM!!!! I have a '00' 3500 with the same scenario. Rear tank pump is seemly always on, can't tell about the front tank. It could be 'magic', but I would not think that we are that lucky. I can assure you of this: It will cost a small fortune to repair the damned thing when it leaves you stranded on the GW Bridge in Rush Hour! The KISS philosophy seems to be sooooooooo absent in any thing we have available today!!!!
My OBD won't deal with it! Computer controlled and that is all you need to know.


Thanks Rich! That sounds like a grand to tell you the fuel computer is having a bad day, along with the rear tank fuel pump. 2500 will probably REPAIR it........BOHICA!!!!

Decided to give the cluster a try. I have a 02 2500hd, I'll pull the cluster out and try it in the 3500 next weekend.
Thanks for the help.

I started the dump today in preparation to swap out the cluster and found the fuel gauge is now working again. I'll keep you all updated if things change.

Nice. It's always good when ya can scare things into workin right. Worked with my kids for years.

Yep - stepper motors in those clusters are notorious piles of *censored*. Usually you can replace them individually without shitcanning the entire cluster. You'll find hundreds of them on eBay, if that tells you anything.