Fuel Filter Module Pressure Sensor, Component Description - Mercedes-Benz OM 471 Introduction Into Service Manual

GF47.50>W>4110H
ENGINES 471.9 in MODEL 963
Location
B638 Fuel filter module pressure sensor
The fuel filter module pressure sensor
(B638) is on the left>hand side of the
crankcase at the fuel filter module.
Task
With the aid of the fuel filter module pressure sensor (B638) the
engine management control unit (MCM) (A4) can detect whether
the fuel filter element needs to be changed. The fuel filter module
pressure sensor (B638) is also used for diagnostic purposes.
Design
The fuel filter module pressure sensor (B638) is a so>called
semiconductor pressure sensor which detects the fuel pressure in
the fuel filter module using the piezo>electric principle. This
consists of 4 pressure>dependent resistors (strain measuring
resistors) which are arranged in a silicon membrane, and an
electronic analysis system which is supplied with a 5 V DC voltage
via the engine management control unit (MCM).
i Introduction of engine OM 471 and exhaust aftertreatment > 09/2011 >

Fuel filter module pressure sensor, component description

– This printout will not be recorded by the update service. Status: 09 / 2011 –
System components
Function
The fuel pressure acts upon the silicon membrane with the four
pressure>dependent resistors and deforms it. The resistors in the
silicon membrane are arranged in such a way that 2 resistors are
contracted and 2 resistors are elongated when the sensor
membrane is deformed.
Contraction and elongation changes the electrical resistance of
the resistors which in turn has effects upon the measurement
voltage, which is being applied to the electronic analysis system.
The electronic analysis system amplifies the measuring voltage,
compensating for possible temperature fluctuations and
manufacturing tolerances in the resistors. The measuring voltage
which has been "cleaned" in this way is forwarded to the engine
management control unit (MCM) (A4), which uses it to derive the
current fuel pressure in the fuel filter module and the load
condition of the fuel filter element.
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