Welcome, and thanks for using Just Answer. I am Cam, and I will do my best to assist you. When you are finished please click on accept only if you are satisfied. I don't get paid unless you do.Please do not accept if you cannot leave positive feedback. I don't know if you are a tech or a just working on your own vehicle so we may have to fine tune the answer. I only know as much about your problem as you have told me in your post, so my answers will be based on what you tell me so please add all the details you can. About your vehicle, I suggest you test the resistance of the rear fuel tank. If that is out if spec, this will be the result.
This bulletin is being revised to update part usage for C/K 3500 Models in the Parts information. Please discard Corporate Bulletin Number 01-06-04-037A (Section 06 -- Engine/Propulsion System).
Some customers may comment on inoperative secondary fuel tank transfer pumps. In some instances, customers may experience multiple failures of the service replacement pumps.
This condition may be caused by the "Four Minute Final Pump Out" feature of the fuel level control module. This feature can command the transfer pump to on when there is no fuel in the secondary tank.
This command occurs with every ignition cycle for a period of four minutes. These transfer pumps can overheat and become inoperative when they are run dry.
Customers that never add fuel to the secondary tank can further compound this issue. In these cases, the secondary pump would become inoperative in a very short period of time.
Three new transfer pump modules have been released to correct this condition. The new module curtails the "Four Minute Final Pump Out" feature. When the sender in the secondary tank drops to a resistance reading of 2 ohms, the pump-out feature is disabled. At resistance readings greater than 2 ohms, the pump-out feature will continue to function. However, under this condition there should be enough fuel in the tank to prevent pump failure. Replace the fuel transfer module using the procedures and part numbers listed below
Module, Fuel Transfer
C6-7 Conventional Models with Gas Engine
F6-7 Tilt Cab Models with Diesel Engine
1998-2001 C/K 3500 with Gas Engine
1996-1997 C/K 3500 with Gas Engine
1996-2001 C/K 3500 with Diesel Engine