Duel fuel tanks

Anthony J Clayton · October 2, 2023

I recently purchased a 2015 Chevy 3500 with a 6.6 Duramax diesel flat bed. I have two tanks front and rear is there a transfer switch? how much fuel in each tank. The fuel gauge said half full attempted to fill the front tank and it would not take any fuel it was full put 31 gallons in the rear tank and the fuel gauge now reads full. How does this system work?

64BAwagon · October 2, 2023

I believe theres a transfer pump and the system uses the rear tank first.

newdude · October 2, 2023

ECM controlled, there is an electric transfer pump. In short, ECM pumps down the rear tank to fill the front tank based on the level in the front tank.

Front tank is 23.5 gallons, rear tank is 40 gallons.

How it works for 2015 trucks. Note, there are two different fuel system calibrations that year so it will operate one of the two following ways:

Fuel System Calibration 12667411 and Earlier

The fuel transfer pump is located on the left frame rail between the fuel tanks. The ECM provides ignition positive voltage to the coil side of the fuel transfer pump relay. The ECM energizes the fuel transfer pump relay, which applies power to the fuel transfer pump. When the primary (front) fuel tank level is less than 64 liters (16.9 gallons) and the secondary (rear) fuel tank level is greater than 10 liters (2.6 gallons), the fuel transfer pump is commanded on and continues to transfer fuel to the primary fuel tank until the primary fuel tank level reaches 79 liters (20.9 gallons) and then the fuel transfer pump is commanded OFF. When the secondary fuel tank level drops below 10 liters (2.6 gallons) and the primary tank is below 79 liters (20.9 gallons), the ECM commands the fuel transfer pump on for 300 s to pump the remaining fuel to the primary fuel tank.

Fuel System Calibration 12676142 and Later

The fuel transfer pump is located on the left frame rail between the fuel tanks. The ECM provides ignition positive voltage to the coil side of the fuel transfer pump relay. The ECM energizes the fuel transfer pump relay, which applies power to the fuel transfer pump. When the primary (front) fuel tank level is less than 72 liters (19 gallons) and the secondary (rear) fuel tank level is greater than 5 liters (1.3 gallons), the fuel transfer pump is commanded on and continues to transfer fuel to the primary fuel tank until the primary fuel tank level reaches 74 liters (19.5 gallons) and then the fuel transfer pump is commanded Off. When the secondary fuel tank level drops below 5 liters (1.3 gallons) and the primary tank is below 72 liters (19 gallons), the ECM commands the fuel transfer pump on for 180 s to pump the remaining fuel to the primary fuel tank.

Edited October 2, 2023 by newdude

cfell · October 2, 2023

Ford has better idea… again. A switch for front/rear tank… but that put’s responsibility on whoever is steering

newdude · October 3, 2023

On 10/2/2023 at 2:11 PM, cfell said:

Ford has better idea… again. A switch for front/rear tank… but that put’s responsibility on whoever is steering

And when was the last time Ford had that? Snooping around info on the latest F450/550 chassis cabs, I don't see a tank selector switch anymore.

Anthony J Clayton · October 4, 2023

On 10/2/2023 at 11:39 AM, newdude said:

ECM controlled, there is an electric transfer pump. In short, ECM pumps down the rear tank to fill the front tank based on the level in the front tank.

Front tank is 23.5 gallons, rear tank is 40 gallons.

How it works for 2015 trucks. Note, there are two different fuel system calibrations that year so it will operate one of the two following ways:

Fuel System Calibration 12667411 and Earlier

The fuel transfer pump is located on the left frame rail between the fuel tanks. The ECM provides ignition positive voltage to the coil side of the fuel transfer pump relay. The ECM energizes the fuel transfer pump relay, which applies power to the fuel transfer pump. When the primary (front) fuel tank level is less than 64 liters (16.9 gallons) and the secondary (rear) fuel tank level is greater than 10 liters (2.6 gallons), the fuel transfer pump is commanded on and continues to transfer fuel to the primary fuel tank until the primary fuel tank level reaches 79 liters (20.9 gallons) and then the fuel transfer pump is commanded OFF. When the secondary fuel tank level drops below 10 liters (2.6 gallons) and the primary tank is below 79 liters (20.9 gallons), the ECM commands the fuel transfer pump on for 300 s to pump the remaining fuel to the primary fuel tank.

Fuel System Calibration 12676142 and Later

The fuel transfer pump is located on the left frame rail between the fuel tanks. The ECM provides ignition positive voltage to the coil side of the fuel transfer pump relay. The ECM energizes the fuel transfer pump relay, which applies power to the fuel transfer pump. When the primary (front) fuel tank level is less than 72 liters (19 gallons) and the secondary (rear) fuel tank level is greater than 5 liters (1.3 gallons), the fuel transfer pump is commanded on and continues to transfer fuel to the primary fuel tank until the primary fuel tank level reaches 74 liters (19.5 gallons) and then the fuel transfer pump is commanded Off. When the secondary fuel tank level drops below 5 liters (1.3 gallons) and the primary tank is below 72 liters (19 gallons), the ECM commands the fuel transfer pump on for 180 s to pump the remaining fuel to the primary fuel tank.

Thanks you the MAN this really helps

On 10/2/2023 at 11:39 AM, newdude said:

ECM controlled, there is an electric transfer pump. In short, ECM pumps down the rear tank to fill the front tank based on the level in the front tank.

Front tank is 23.5 gallons, rear tank is 40 gallons.

How it works for 2015 trucks. Note, there are two different fuel system calibrations that year so it will operate one of the two following ways:

Fuel System Calibration 12667411 and Earlier

The fuel transfer pump is located on the left frame rail between the fuel tanks. The ECM provides ignition positive voltage to the coil side of the fuel transfer pump relay. The ECM energizes the fuel transfer pump relay, which applies power to the fuel transfer pump. When the primary (front) fuel tank level is less than 64 liters (16.9 gallons) and the secondary (rear) fuel tank level is greater than 10 liters (2.6 gallons), the fuel transfer pump is commanded on and continues to transfer fuel to the primary fuel tank until the primary fuel tank level reaches 79 liters (20.9 gallons) and then the fuel transfer pump is commanded OFF. When the secondary fuel tank level drops below 10 liters (2.6 gallons) and the primary tank is below 79 liters (20.9 gallons), the ECM commands the fuel transfer pump on for 300 s to pump the remaining fuel to the primary fuel tank.

Fuel System Calibration 12676142 and Later

The fuel transfer pump is located on the left frame rail between the fuel tanks. The ECM provides ignition positive voltage to the coil side of the fuel transfer pump relay. The ECM energizes the fuel transfer pump relay, which applies power to the fuel transfer pump. When the primary (front) fuel tank level is less than 72 liters (19 gallons) and the secondary (rear) fuel tank level is greater than 5 liters (1.3 gallons), the fuel transfer pump is commanded on and continues to transfer fuel to the primary fuel tank until the primary fuel tank level reaches 74 liters (19.5 gallons) and then the fuel transfer pump is commanded Off. When the secondary fuel tank level drops below 5 liters (1.3 gallons) and the primary tank is below 72 liters (19 gallons), the ECM commands the fuel transfer pump on for 180 s to pump the remaining fuel to the primary fuel tank.