What is a fuel level sending unit?
The fuel level sending unit is located in the fuel tank, and sends a constant signal indicating the amount of fuel that remains in a fuel tank.
How does the fuel level sending unit work?
In most systems, the fuel level sensor will have a mechanical arm extending to the top of the fuel inside the tank. It will float on the top of the fuel, and as the arm moves down, the signal strength from the sending unit decreases. That information is eventually sent to the fuel level gauge for driver awareness. When the arm gets low enough, the light on the dashboard will be turned on, alerting the driver to stop for fuel.
What are the symptoms related to a bad fuel level sending unit?
When the fuel level sending unit fails, the fuel gauge will fail to operate, and, in some vehicles, the check engine light may illuminate. The on-board diagnostic (OBD) trouble codes stored will be relative to the fuel level sensor if the check engine light does illuminate. As no other symptoms rely on the fuel tank level, no other symptoms are expected.
Can I drive with a fuel level sending unit problem?
The vehicle can be driven without the fuel gauge. Most people use the trip meter and fill up the gas tank every time they reach their prefered mileage. The biggest risk is carrying gasoline or diesel fuel inside of the vehicle, or in the trunk. If gasoline is carried in case you run out, it must be outside the vehicle. The fumes inside the vehicle can cause injury and death.
How often do fuel level sending units need to be replaced?
Fuel level sending units are hardly ever faulty, and require no maintenance throughout their lifecycle. Most vehicles on the road today will never have sending unit failure.
How are fuel level sending unit issues diagnosed?
Suspected fuel level sending units are normally a very quick diagnosis. The servicing technician will immediately test the system, and verify that the gauge is working properly when the proper conditions are applied to the circuit. If the gauge and all fuses are in working order, the voltage from the fuel sending unit will be compared to specifications, and electrical connections will be verified. The readings from the sensor will indicate if failure has occurred once the remainder of the system is verified in good working order.
How is a fuel level sending unit replaced?
The fuel level sending unit must be removed from the fuel tank. In most vehicles, there is a service access panel underneath the trunk linking, or back seat, however, this is not always the case. Some vehicles require the fuel tank to be removed in order to access the fuel sending unit. Often, the sending unit and fuel pump must be replaced together. They are unbolted from the fuel tank, and disconnected from fuel and electrical connectors. Note, the technician will disconnect the battery prior to accessing the fuel pump. The new pump is inserted, connected, and tested prior to reassembly of the vehicle.
The Fuel Level Sending Unit may be attached to the fuel pump assembly and require removal of the fuel tank to gain access. It this case, if changing the sending unit it may be wise to change the fuel pump as well.
Poor quality fuel can cause deposits to form on the Fuel Level Sensor contacts, affecting proper operation of the sensor.
RepairPal Recommendations for fuel level sending unit issues
Prior to installing the fuel level sending unit into the fuel tank, we recommend comparing the movement of the old to the movement of the new fuel level sending unit. If one moves farther in either direction, the arm should be adjusted to ensure the proper level will display on the gauge.
