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Module - Powertrain control
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Sensor - Engine coolant temperature
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Sensor - crankshaft position
Component Description and Operation
The electronic engine control system comprises a powertrain control module (PCM), sensors and actuators. The sensors supply the PCM with input signals which relate to engine operating conditions and the actuators respond to output signals received from the PCM. These output signals are based on the evaluated input signals which are compared with calibrated data tables or maps, stored in the PCM, before the output signal is generated.
Powertrain Control Module (PCM)
All variants utilise a 104 pin PCM (EEC V) which provides precise control of basic engine calibration parameters at all load and speed points throughout the range of ambient intake air temperatures and pressures.
Throttle Position Sensor
The throttle position sensor is a rotary potentiometer which is secured to the throttle body and operated by the throttle plate shaft. The throttle position sensor is supplied with a reference voltage by the PCM. When the throttle plate is opened, a sliding contact moves over a resistance track changing the output voltage. The output voltage is assigned to a corresponding throttle plate position by the PCM.
Idle Air Control Valve
The idle air control valve is an electronically controlled solenoid valve which allows a flow of air to bypass the throttle plate. Engine speed can, therefore, be maintained irrespective of engine load. The idle air control valve is controlled by grounding pulses from the powertrain control module, the length of which determines the position of the valve.
Camshaft Position Sensor
The camshaft position sensor is an inductive pulse generator which scans a reference cam on the camshaft. The camshaft position sensor sends an alternating voltage signal to the powertrain control module from which the position of number one cylinder is calculated. The signal from the camshaft position sensor is required only during starting. When the engine is running, the profile ignition pick-up (PIP) signal is used to sequentially control the fuel injectors.
Mass Air Flow Sensor
The mass air flow sensor measures the mass of air entering the intake system, the measurement being based on the constant temperature hot wire principle. Suspended in a bypass duct are a hot wire probe and an air temperature probe. The powertrain control module ensures that the hot wire probe is always 200°C hotter than the air temperature probe. The hot wire probe is cooled by the air flowing through the intake system and the powertrain control module varies the heating current to maintain the 200°C temperature difference. The change in heating current is measured as a voltage drop across a precision resistor and is assigned to a corresponding mass air flow calculation by the powertrain control module.
Intake Air Temperature Sensor
The intake air temperature sensor is a temperature dependent resistor which has a negative temperature coefficient i.e. it's temperature changes inversely with respect to ambient temperature. The intake air temperature sensor is supplied with a reference voltage by the powertrain control module. When the intake air changes temperature, the resistance of the sensor changes thus changing the output voltage. The output voltage is assigned to a corresponding intake air temperature by the powertrain control module.
Engine Coolant Temperature Sensor
The engine coolant temperature sensor is a temperature dependent resistance which has a negative temperature coefficient i.e. it's temperature changes inversely with respect to temperature. The engine coolant temperature sensor is supplied with a reference voltage by the powertrain control module. When the engine coolant temperature changes, the resistance of the sensor changes thus changing the output voltage. The output voltage is assigned to a corresponding engine coolant temperature by the powertrain control module.
Crankshaft Position Sensor
The crankshaft position sensor is an inductive pulse generator which scans 36-1 cast protrusions on the flywheel. Minus one means that one of the cast protrusions is missing and this gap is located at 90° before top dead centre. This gap is used by the powertrain control module as a reference for crankshaft position. The crankshaft position sensor sends an alternating voltage signal to the powertrain control module where it is converted and becomes the digital, profile ignition pick-up (PIP) signal.
Heated Oxygen Sensor (Petrol Variants Only)
The heated oxygen sensor is a voltage generator which is installed ahead of the catalyst in the exhaust flow. When the air/fuel ratio is ideal (theoretically 14.7:1) or Lambda 1 a voltage signal of 450 mV is sent to the powertrain control module. When the mixture is lean, the voltage signal is reduced to 200 mV and the powertrain control module sets the air/fuel mixture towards rich. When the mixture is rich, the voltage signal is increased to 800 mV and the powertrain control module sets the air/fuel mixture to lean, and so on, thus close control of exhaust emissions is achieved. To ensure the heated oxygen sensor quickly reaches it's operating temperature of 300°C, it is equipped with a heating element which operates when the ignition is switched on.
Needle Lift Sensor (TCI Diesel Only)
This provides the powertrain control module with a signal, indicating the position of the injector pintle. This input is used to establish the correct fueling requirements.
