Theory Of Operation

The Fuel Level Sensor information is a bussed message to the Powertrain Control Module (PCM) from the Body Control Module (BCM). The fuel level rationality will set a fault for a fuel level reading that does not change over an accumulated mileage threshold to keep stuck high or stuck low fuel levels from disabling OBD monitors. If the vehicle is fitted with a saddle tank fuel system this feature includes diagnostics for both of the sending units and diagnostics for a siphon tube that has become disconnected or plugged. The power up test looks to see a large enough fuel level voltage change from the last key-off to the following engine run. The engine run test looks to see a fuel level voltage change over an accumulated mileage.

Vehicles fitted with saddle fuel tank configurations have two Fuel Level Sensors. The primary side of the tank has the filler tube inlet near the bottom and contains the Fuel Pump Module. During fuel tank fills, fuel must overflow the primary side to reach the secondary side of the tank. As fuel is consumed, a siphon tube is used to draw fuel from the secondary side to the primary side. Because the siphon tube flow rate exceeds the fuel consumption rate, the secondary side of the tank will be empty before fuel is depleted from the primary side. Fuel Level Sensor 1 is located on the primary side of the tank. Fuel Level Sensor 2 is located on the secondary side of the tank.