Secondary Fuel Pump - Dual Tanks

WARNING: This page is about a different car, the 2004 GMC Sierra, 2004 GMC Cab & Chassis Sierra, 2004 Chevrolet Silverado, and 2004 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.

The secondary fuel pump is a low pressure electric transfer pump. The secondary fuel pump is mounted outside the fuel tank on the left side of the body crossmember. The secondary fuel pump transfers fuel from the secondary fuel tank to the primary fuel tank when commanded by the powertrain control module (PCM). The PCM grounds the secondary fuel pump relay control circuit. Fuel level is continuously monitored in both tanks by the PCM. When the fuel level in the primary tank is approximately 2 gallons lower than that in the secondary tank, the secondary fuel pump is energized and approximately 4 gallons of fuel is transferred to the primary tank. The above actions continue until the primary tank fuel level is low enough that it will accept all of the remaining fuel in the secondary tank, at which time the secondary fuel pump is energized until the secondary tank is empty.