Fuel gauge sensor - RA4700FLH0020X(47-0020)

WARNING: This page does not describe the selected car, but rather 42 other vehicles, including the 1999 Mercedes-Benz S600, 1999 Mercedes-Benz S500, 1999 Mercedes-Benz S420, 1999 Mercedes-Benz S320, and 1999 Mercedes-Benz CL600. However, it is still accessible from the selected car via links, so may be relevant.

Model 124

Fig 1: Function Of Fuel Gauge Sensor Components (Model 124)
Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

As the fuel level drops, the variable resistance is increased by the float (2) moving down, as a result of which the voltage drops and the needle of the gauge in the instrument cluster moves back.

If the fuel level drops to the reserve quantity, the reserve warning contact closes (5) and switches ground to the reserve warning lamp, as a result of which this lamp lights up when the engine is running.
Models 129, 140
NOTE: The reserve warning lamp lights up with a weak light as a check function, with a strong light to indicate reserve quantity.

Testing fuel gauge (54-257) .

Fig 2: Function Of Fuel Gauge Sensor Components (Models 129, 140)
Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

Shown on model 129

As the fuel level drops, the variable resistance is increased by the float (2) as it moves down, as a result of which the voltage drops and the needle of the gauge in the instrument cluster moves back.

If the fuel level drops to reserve quantity, the reserve warning lamp is switched on by electronics in the gauge. As the reserve quantity decreases, the needle moves in the reserve field of the gauge to the end stop (dynamic indication). The reserve warning lamp lights up when the ignition is switched on (check function). As soon as the engine is running, it goes out provided the fuel tank contains more than the reserve quantity.

NOTE: The reserve warning lamp lights up with a weak light as a check function, and with a stronger light to indicate reserve quantity.

Testing fuel gauge (54-257) .