Fuel Level Sensor: Description and Operation

Fuel Level Sensor

There are two parts to the fuel level sensor monitor. The output of the fuel level sensor is monitored to detect if its output does not change as fuel is used. It is also monitored when the vehicle is stationary and fuel movement is expected to be at a minimum to check for a noisy signal.

Fuel Level Stuck Monitor
The fuel level is monitored continuously and it needs to change by more than a set percentage before a calculated amount of fuel is used. This process will operate through cumulative trips if necessary. Once the fuel level changes by the amount required the process is reset and starts again. If the fuel used threshold is reached before the fuel level changes by the required percentage, a temporary fault will be stored. A second occurrence will cause the Malfunction Indicator Lamp (MIL) to be illuminated.

Fuel Level Noisy Monitor
Once the fuel level percentage has changed to satisfy the stuck monitor described above and a few other entry conditions have been met, the system will complete a fuel level noisy test in the next available idle period. When the vehicle comes to rest the fuel movement will be allowed to subside. The output of the fuel level sensor will be monitored for a short period. During this period the output of the fuel level sensor will be integrated and compared to a threshold, which is set to find faulty fuel level sensors. This process is repeated as the fuel level falls. If the failure threshold is exceeded a first trip temporary failure flag will be set.

A further failure in the next trip will illuminate the MIL.