Accelerator pedal (AP) position sensor
The accelerator position sensor is mounted by the pedal box in the passenger compartment and makes a mounting for accelerator pedal. Its main task is to supply the Engine control module (ECM) with information about the position of the accelerator pedal.
The accelerator pedal position sensor consists of two internal sensors, where one generates an analog signal and the other a pulse width modulated signal (PWM). The purpose of having two types of sensor is to eliminate the probability of a fault from both signals from the sensors being incorrect, at the same time as them showing the same pedal position and the control module considers them correct.
The analog sensor supplies the Engine control module (ECM) with a signal that is approximately 0.5 V when the pedal is released and approximately 4.5 V when fully depressed. The sensor receives a voltage supply (5 V) and ground from the Engine control module (ECM).
The pulse width modulated (PWM) sensor supplies both the Engine control module (ECM) and Electronic throttle module (ETM) with a signal that has a fixed frequency of approximately 200 Hz where the pulse ratio varies between 8-88 %, depending on the position of the accelerator pedal.
The sensor receives voltage supply (12 V) via the main relay and is grounded via its own ground terminal. the signal to the Electronic throttle module (ETM) is electrically routed via the Engine control module (ECM), however, without affecting the signal at all.
The Engine control module (ECM) first uses the analog signal from the accelerator position sensor to calculate the desired throttle angle. The Engine control module (ECM) then transmits this request about the desired throttle angle via the CAN to the Electronic throttle module (ETM), which then fulfils the desired throttle angle and transmits back the information about the current throttle angle.
The pulse width modulated signal is used to monitor the analog signal. If there is a fault in the analog signal, the system uses the pulse width modulated (PWM) signal instead.
There are also situations when the PWM signal is used to control the throttle angle without a fault being detected on the analog signal. For example, when a fault has occurred in CAN communication between the Engine control module (ECM) and the Electronic throttle module (ETM), the throttle unit then does not receive any desired throttle angles from the Engine control module (ECM) but must then rely on the directly connected PWM signal to control the throttle.
On vehicles equipped with an automatic transmission, the sensor also contains a mechanical kick-down resistor that gives the driver a kick-down feeling when the pedal is depressed approximately 80 % of full pedal stroke. In this pedal position, the Transmission control module (TCM) permits kick-down to be activated. There is no separate switch in this sensor for kick-down.
To determine if the analog and the PWM signal are fault free, the Engine control module (ECM) and Electronic throttle module (ETM) carry out electrical checks and plausibility checks of the signals. If a fault is detected on any of the signals, the system uses the other signal.