[G.M.Landscaping]

2004 Silverado 3500 with dual tanks. Fuel gauge reading empty and low level light on.
Go to gas station and try filling rear tank. Wouldn't take anymore. Was filled up already. Front tank took 18 gallons. Light still on and reading empty.
So what ive been reading is a bad front level sender, bad balance module, bad rear pump, etc.
Where to start. Its a dump so I can lift bed to get to stuff easily.
I've read fuel level sensor is in front tank only. Also that rear should be filling front as front goes down.

 

[SilverPine]

Transfer pump.

 

[m_ice]

Theres a relay under the dash on the driver side that it could be.

 

[G.M.Landscaping]

So I had a look today. I decided to tap on both tanks on top where the lines go in to see if that would maybe make either sender or pump work. Only made the rear tank lines start leaking from rust. So it needs replaced definitely now. I removed the rear pump assembly and tested pump. It worked fine. I tested continuity/resistence on fuel level sender and it seemed to be working correctly also. It gave different resistance reading through out sweep range.
Tested from all wires on pump assembly and all tested good.
So I ordered a complete rear pump assembly. Be a couple days.
I believe when its installed it will not solve anything except for the lines that were rusting.
I unplugged front pump wiring and plugged it into the rear assembly to see if gauge worked, and it was still on empty with light on.

 

[G.M.Landscaping]

Theres a relay under the dash on the driver side that it could be.

I still need to look for this.

 

[G.M.Landscaping]

Also, how do I know if I have EEC(evaporative emission control).
I think I ordered the wrong one.
They ordered one for no sec

 

[zlssefi]

I had this same problem with a 2001 3500. The front sender and pump went bad so i replaced it. A new problem arose in which the guage would read half full, yet the truck would run out of gas. putting 5 gallons in the front tank the truck would run again. I had the sender replaced under warranty. Same problem so i dug into it myself. The new sender module arm was getting hung up on the side of the tank so it would get stuck at half tank, hence not telling the rear tank it needed fuel. Chances are replacing the front sender module would cure your problem, but check the float arm clearance when you install.