Operation of oil pressure gauge - RA1800104A090X(18-0090)

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.

Models 129, 140

Fig 1: Identifying Operation Of Oil Pressure Gauge
Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

The two-pin oil pressure sensor (B5) in the oil filter (10) converts the engine oil pressure which exists into a resistance. As the oil pressure increases, the resistance increases also. The resistance and engine speed are supplied as input signals to the microprocessor (a) in the electrical base plate of the instrument panel unit (A1).

If the oil pressure drops at a certain engine speed with the result that the resistance drops below a certain level, the oil pressure pointer moves to the bottom stop (0) and the warning lamp (8) comes on.

The oil pressure gauge also moves to the bottom stop (0) in the event of an open circuit in the wiring, but without the warning light (8) being operated.

The microprocessor (a) analyzes the two input signals relative to the stored characteristic curve from an engine speed of >1200 rpm. Depending on the relevant evaluation, the angle position of the pointer of the oil pressure gauge (A1p3) is controlled across the scale with the readings 0, 1, 2 and 3.

The oil pressure sensor (B5) is connected to ground at the base plate and to the microprocessor (a) by means of the connector (X27). Voltage is supplied to the base plate through the ignition lock (S2/1), the fuses (5 and 9) in the fuse box (F1).