Mercedes-Benz 400E Fuel Level Sending Unit Replacement Cost

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.

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.

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.

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.

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.

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.

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.

Fuel contaminants play a large role in the health of an engine and fuel system. It is best to ensure you are adding fuel of the appropriate grade for your engine, according to the instructions in the owner's manual. When working with fuel, the battery should always be disconnected, and proper precautions taken against fire hazards.

Some fuel level sending units are difficult to replace, and some are simple. The level of difficulty will be described by the repair procedure for the particular vehicle, but most can be accomplished within an hour. If there is no service port for the fuel tank, the fuel tank must be removed. Fuel tanks are large, cumbersome, and can be extremely heavy. If the fuel tank must be replaced, a DIYer can handle the repair, but an assistant should be used to prevent injury or damage to the vehicle. The fuel tank combines electricity and fuel, and proper working knowledge of these components, and safety procedures is a must. If you feel that you are unqualified for this task, leave it to a professional technician.