Acceleration Control - TDV8 3.6L Diesel (G938534)

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The 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 controller area network (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 anti-lock brake system (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.