Input Signals

Input signals





Sensors and functions which are different to previous types are marked in bold text .










Fuel trim
Control of the fuel/air mixture occurs using known principles. However the signal from the front probe is now of a linear character. This means that the engine control module (ECM) notices small changes throughout the voltage range and can control the fuel/air mixture much faster and more precisely than before.
Both heated oxygen sensors (HO2S) contain as before a PTC resistor which is supplied with voltage from the engine control module (ECM) in order to reach operating temperature quickly.
If the engine control module (ECM) determines that the ambient air is very cold and damp it may delay starting to heat up the heated oxygen sensors (HO2S) a few minutes. This is to prevent the heated oxygen sensor (HO2S) warm ceramic being touched by cold drops of water and then cracking.
The oxygen sensitive ceramic which measures oxygen levels in the exhaust gases consists of Zirconium dioxide.

Front heated oxygen sensor (HO2S)
The output signal characteristic is between 0 - 4.7V.
The short-term fuel trim control lies between 0.75 and 1.25.
Signal characteristics:
- low voltage = rich mixture
- high voltage = lean mixture

Rear heated oxygen sensor (HO2S)
The rear heated oxygen sensor (HO2S) operates with the same signal characteristics as previously, but has gained more importance for controlling the fuel/air mixture. The rear heated oxygen sensor (HO2S) has been moved forward nearer to the front heated oxygen sensor (HO2S), just in front of the metal monolith in the catalytic converter.

Camshaft Position (CMP) Sensor
The camshaft position (CMP) sensor is a new version and operates using a different signal characteristic to previously.
- The sensor consists of an MRE (Magnetic Resistance Element). It is a permanent magnet with 2 special resistors which are connected in series with each other, where one end is voltage supplied and the other goes to ground. The output signal is an analog sine curve which passes through an analog/digital converter in the camshaft position (CMP) sensor before being sent on to the engine control module (ECM).
- When a tooth on the pulse wheel nears the sensor the magnetic field is bent and affects the resistor located nearest to the ground, resistance affects the voltage and the output signal to the Engine Control Module (ECM) is low. When the same tooth continues past the sensor the magnetic field follows and so affects the other resistor which is located nearest to the voltage supply, this resistor affects the voltage so that the output signal to the Engine Control Module (ECM) is high. The magnetic field swings backwards and forwards between the teeth on the pulse wheel and the engine control module (ECM) senses the signals between the teeth, partly before and partly after the sensor.
- The pulse wheel has 4 teeth. The engine control module (ECM) calculates the time interval from one tooth to the next and can decide exactly which cylinder must be supplied with fuel and spark respectively.