Function of the oil pressure indicator - ra18001200090x(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.

Engine 120 in Model 140

Model 140

Fig 1: Function Of Oil Pressure Indicator - Model 140

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

The two-pin oil pressure sensor (B5) in the oil filter (10) converts the existing engine oil pressure into an ohmic resistance. As the oil pressure rises, the ohmic resistance increases. Resistance and engine speed are passed as input signals to the microprocessor (a) in the electrical base plate of the instrument panel unit (1).

The microprocessor (a) analyzes the two input signals relative to the stored characteristic curve from an engine speed of >1200 ± 60/min. Depending on the respective analysis, the angle position of the oil pressure pointer of the oil pressure indicator (A1p3), is controlled across the scale with the values 0, 1, 2 and 3.

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 lower stop (0) and the warning lamp (8) lights up.

The oil pressure pointer also moves to the bottom stop (0) if there is an open circuit in the wiring, although the warning lamp (8) does not come on.

The oil pressure sensor (B5) is connected to ground at the base plate and to the microprocessor (a) by the plug connections (X27, X18, X24).

Voltage is supplied to the base plate through the ignition lock (S2/1), fuse 17 in the fuse box (F3).