Electric Throttle
The electric throttle is located between the charge cooler connecting pipe and the intake manifold, the electric throttle is secured to the manifold with four Torx head bolts.
The electric throttle comprises the throttle body, a round throttle butterfly valve which is actuated by a motor and a Throttle Position (TP) sensor. The electric throttle is controlled by the PCM which receives positional signals from the TP sensor.
If a failure of the motor occurs, the butterfly valve is returned to an emergency position by springs. The butterfly valve remains partially open with limited engine speed available to the driver.
The electric throttle has 5 wires which are connected to the PCM. Two wires supply 12V current and ground for the Direct Current (DC) motor. Three wires are connected to the TP sensor. One wire supplies a 5V reference voltage to an analogue, Hall Effect sensor. Two further wires provide the TP sensor negative and positive signal feedback to the PCM. As the throttle angle increases, the output of the negative sensor decreases and the output of the positive sensor increases.
The motor is a Direct Current (DC) stepper motor which drives a gear wheel and two springs; one for opening and one for closing. The motor rotates the spindle to which the butterfly valve is attached. PWM signals from the PCM control the motor to adjust the position of the butterfly valve, regulating the amount of air entering the inlet manifold for combustion. Movement of the motor is achieved by changing the polarity of the power supply to the DC motor, allowing it to be operated in both directions. The butterfly valve and the DC motor has two maximum positions; butterfly valve closed which allows minimal air flow through the electric throttle into the intake manifold and butterfly valve open which allows maximum air flow into the intake manifold.
The PCM calculates the butterfly valve position by comparing the feedback signal from the TP sensor to a stored value at a known datum position. The PCM performs a self test and a calibration routine on the butterfly valve position at each ignition cycle. This is achieved by the PCM powering the DC stepper motor to fully close the butterfly valve and, if required, fully open the butterfly valve.
The PCM monitors the DC stepper motor and the TP sensor for faults and can store fault related Diagnostic Trouble Codes (DTC). The codes can be retrieved using an approved diagnostic system. In the event of a fault the engine Malfunction Indicator Lamp (MIL) in the instrument cluster will also be illuminated.