hey everyone. I'm new here so bear with me. I just bought a 2003 C5500 and tried and tried to fill the truck up and fuel kept spilling out. The gauge reads empty so I thought there was something in the line. I pulled the inlet off the fuel tank and diesel poured out. Tanks are full. So whats the problem. When I turn the ignition on the gauge jumps up to "E". so the gauge works. Anyone know how to correct this problem and how to avoid it in the future?

Matt

If the PCM detects a problem in the system such as the transfer pump going out, sending unit malfunction, etc., it will set a code and shut off the pump and gauge. On the 03's and early 04's GM originally programmed the PCM to disable the system if it detected the fuel levels changing in the tanks, but the change in fuel level wasn't accounted for by fuel useage. Example, if you were refueling the truck with the engine running the PCM would see the rapid change in fuel level and that didn't make sense to it (because it is Federal Law that you must shut off the truck while refueling) so to avoid a spill or leak, it would shut off the transfer pump system the gauge and set a code. They have since came out with a reflash of the PCM that doesn't do all of that if you refuel the diesels while the engine is running, but yours may not have had the reflash. The gas trucks are still that way. Don't you just love lawyers?

You probably need to have a dealer look at it. It may need the updated program or you might have a bad sending unit or transfer pump.

Thanks Dirt. I'll take it in

I had a Chevy dealer clear my codes and he didn't even charge me. John

I have a 2006 Duramax/Alison 3500 dually and my fuel gauge goes to zero while driving. Seems like the ambient temp needs to be 85 and the veh. at operating temp. A quick shut down and restart doesn't fix it. But having it off for 15 + minutes and restart it works OK. Maybe the kicker is I have a gravity feed aux fuel tank in the bed that always keeps the OEM tank full. But it never overflows because of float valve in fill hose adapter (from RDS). Because it will reset, I am sure it is a software bug. Dealer thinks it needs a replacement sender unit. But can't find any TSB for 2006. I have 2900 miles on truck. Built Feb 2006.

If the PCM doesn't know you have dual tanks it will only read the one sending unit. As the fuel level doesn't drop in concert with the amount of fuel that the FICM (Fuel Injection Control Module) sees being drawn through it, it throws the code and turns off the gauge.

A suggestion would be to put an electric valve in the feed from the aux tank and when the fuel level drops in the main tank to say 1/4, turn on the fuel feed from the aux tank and refill the main one. That way the PCM thinks you are simply refilling the main tank like you would at a fuel stop. That should get rid of the codes you are seeing.

I have the same thing in my truck, All I do is let the aux tank drain into the main when the aux tank gets empty the fuel gauge starts to work again on its own. Kind of like a reserve tank. When the gauge starts working again I have 40 gal to go till empty!:D