LR3/Disco 3
ACCELERATOR PEDAL POSITION SENSOR
The Accelerator Pedal Position Sensor (APP) is integral to the accelerator pedal assembly.
The APP sensor enables the ECM to determine the throttle position requested by the driver on the accelerator pedal.
The APP sensor is installed on the pedal box and consists of a twin track potentiometer with wipers driven by a linkage
connected to the accelerator pedal. Each potentiometer track has a 5 volt supply and ground connection from the ECM,
and produces a linear signal voltage to the ECM proportional to the position of the accelerator pedal. The signal voltage
from track 1 of the potentiometer is approximately double that of the signal voltage from track 2.
From the sensor signals, the ECM determines driver demand as a percentage of pedal travel, where 0% is with the pedal
released and 100% is with the pedal fully depressed. Driver demand is then used to calculate throttle angle, fuel quantity
and ignition timing. The ECM also outputs driver demand on the CAN system, for use by the brake and gearbox control
systems.
The ECM stores the signal values that correspond with closed and wide open throttle, and adapts to new values to
accommodate component wear or replacement.
The signals from the APP sensor are monitored by the ECM for short and open circuits and plausibility. If a fault is
detected, the ECM:
Stores a related fault code in memory.
Illuminates the SERVICE ENGINE warning lamp in the instrument pack.
Inhibits the driver demand message on the CAN bus, which disables the Hill Descent Control (HDC) function of
the ABS modulator and reduces the performance of the automatic gearbox (harsh gear changes and loss of kick
down).
Adopts a throttle limp home mode.
The throttle limp home mode adopted depends on the nature of the fault:
If a fault is detected with one potentiometer track, the ECM limits vehicle acceleration by limiting throttle plate
opening.
If a fault is detected with both potentiometer tracks, the ECM uses the throttle plate to run the engine at a fixed
speed of 1472 rev/min while the brake pedal is released, and idle speed (750 rev/min) while the brake pedal is
pressed or if there is a brake pedal sensor fault.
If there is a process fault in the ECM, the ECM either uses fuel injection cut-off to limit engine speed to 1300 rev/
min or disables fuel injection to stop the engine.
C0787 Accelerator Pedal Position Sensor Pin Out Table
Pin No
Description
Input/ Output
1
Throttle position 1
Input
2
5 volt reference voltage
Input
3
Throttle position 2
Input
4
Sensor Ground
-
5
Throttle +
Input
6
Throttle -
Input
