Some 2024 Silverado 3500 HD and Sierra 3500 HD models equipped with the 6.6L Duramax Diesel engine (RPO L5P) may have a fuel gauge that drops to empty and an inoperative fuel transfer pump.
During diagnosis, the Engine Control Module (ECM) may show a fuel level percentage higher than empty. For example, it may show a 72.2% fuel level with 45.5 gallons remaining, but the IPC data may show a considerably lower number, such as 9%. The fuel level condition may be caused by insufficient fuel transfer with the dual fuel tank transfer system not transferring fuel properly from the rear tank to the front tank.
Fuel Transfer Inlet Port
The poor fuel transfer from the rear tank to the front tank may be due to a blockage in the fuel transfer inlet port at the A7 Front Fuel Tank Sender Assembly inside the fuel tank. (Fig. 8, #15) The assembly may have an internal check valve within the inlet port blocking the fuel from entering the front tank. If it is found that the A7 Front Fuel Tank Sender Assembly fuel transfer inlet port is blocked, it should be replaced.
Fig. 8
Before installing the new A7 Front Fuel Tank Sender Assembly, inspect it to make sure there isn’t any blockage. Use very low air pressure (below 5 PSI) to determine if the fuel inlet port is blocked or flowing freely.
Fuel Transfer System Diagnosis
When performing basic testing of the fuel transfer system:
- Verify that the fuel transfer pump (Fig. 9) will run electrically by using the scan tool to command the pump on. This test does not confirm that the transfer pump is pumping fuel.
- Use the scan tool to monitor the front tank and rear tank fuel level voltages. Proper fuel level sensor voltages for either tank level sensor are 0.7 volts = full tank and 2.5 volts = empty.
- To determine if fuel is being transferred from the rear tank to the front tank, monitor the fuel level sensor voltages while commanding on, or jumper power and ground to the fuel transfer pump. The fuel level should decrease (voltage increases) in the rear tank and the fuel level should increase (voltage decreases) in the front tank.
Fig. 9
For more details on fuel transfer pump diagnosis, refer to #PIT6159.
Thanks to Jim Will
