Fuel Pressure-temperature Sensor
The fuel pressure-temperature sensor consists of two independent sensors combined in one housing.
The fuel temperature sensor is required to precisely calculate the start of injection and injection quantity. The fuel pressure sensor registers the fuel pressure upstream of the high pressure pump. This fuel pressure is required for the purpose of controlling the fuel pump in the fuel tank.
The fuel pump is also switched off when the engine is turned off and the fuel feed is depressurized. After the fuel pump has been shut down, the digital diesel electronics checks and evaluates the plausibility of the fuel pressure sensor. If a fault is detected, the corresponding fault code is stored in the fault code memory of the digital diesel electronics.
The integrated fuel temperature sensor is identical to the fuel temperature sensor used in the E90. The fuel pressure sensor is also integrated in the housing. Both the fuel pressure sensor and the fuel temperature sensor features two separate connections in a common connector housing that has four pins.
The fuel pressure sensor consists of resistors mounted on a diaphragm. The one side of the diaphragm has contact with the fuel so that the fuel pressure acts on the diaphragm.
The greater the pressure, the more the diaphragm is deflected. The resistors on the diaphragm change their resistance in response to the mechanical stress. A bridge circuit and electronic signal processing circuitry in the sensor amplify the bridge voltage, compensate for temperature influences and linearize the pressure characteristic curve.
The output voltage for the digital diesel electronics is in the range between 0 and 5 volts. As for the temperature sensor, a characteristic curve is stored in the digital diesel electronics that assigns a corresponding pressure to each voltage value.