Accelerator Pedal Position Sensor (App)

Courtesy of JAGUAR CARS, INC.

The accelerator pedal position (APP) sensor is located in a plastic housing which is integral with the throttle pedal. The housing is injection molded and provides location for the accelerator pedal position (APP) sensor. The sensor is mounted externally on the housing and is secured with two Torx screws. The external body of the sensor has a six pin connector which accepts a connector on the vehicle wiring harness.

The sensor has a spigot which protrudes into the housing and provides the pivot point for the pedal mechanism. The spigot has a slot which allows for a pin, which is attached to the sensor potentiometers, to rotate through approximately 90 degrees, which relates to pedal movement. The pedal is connected via a link to a drum, which engages with the sensor pin, changing the linear movement of the pedal into rotary movement of the drum. The drum has two steel cables attached to it. The cables are secured to two tension springs which are secured in the opposite end of the housing. The springs provide 'feel' on the pedal movement and require an effort from the driver similar to that of a cable controlled throttle. A detente mechanism is located at the forward end of the housing and is operated by a ball located on the drum. At near maximum throttle pedal movement, the ball contacts the detente mechanism. A spring in the mechanism is compressed and gives the driver the feeling of depressing a 'kickdown' switch when full pedal travel is achieved.

The accelerator pedal position (APP) sensor signals are checked for range and plausibility. Two separate reference voltages are supplied to the pedal. Should one sensor fail, the other is used as a 'limp - home' input. In limp home mode due to an accelerator pedal position (APP) signal failure the engine control module (ECM) will limit the maximum engine speed to 2000 rpm.

Courtesy of JAGUAR CARS, INC.

The accelerator pedal position (APP) sensor has two potentiometer tracks which each receive a 5V input voltage from the engine control module (ECM). Track 1 provides an output of 0.5V with the pedal at rest and 2.0V at 100% full throttle. Track 2 provides an output of 0.5V with the pedal at rest and 4.5V at 100% full throttle. The signals from the two tracks are used by the engine control module (ECM) to determine fueling for engine operation and also by the engine control module (ECM) and the transmission control module (TCM) to initiate a kickdown request for the automatic transmission.

The engine control module (ECM) monitors the outputs from each of the potentiometer tracks and can determine the position, rate of change and direction of movement of the throttle pedal. The 'closed throttle' position signal is used by the engine control module (ECM) to initiate idle speed control and also overrun fuel cut-off.