Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
2004 Land Rover Freelander (LN) V6-2.5LFACTORY OEM SERVICE PROCEDURE
Accelerator Pedal Position Sensor: Description and Operation
Accelerator Pedal Position Sensor
Description
The APP sensor is used to determine the engine torque demand requested by the driver. The sensor consists of 2 independent potentiometers that produce an output voltage proportional to the angular position of the throttle pedal. Each potentiometer has a separate 5 V supply and ground direct from the ECM.
The ECM determines the driver demand as a percentage of pedal travel, i.e. "foot off" = 0% and full travel = 100%. This information is then used to calculate the percentage of maximum available engine torque demanded by the driver. The ECM will then calculate the throttle angle, fuel quantity and ignition angle required to achieve this demanded torque.
The driver demand information is output on CAN for other systems, in particular to the automatic TCM, which uses this information to determine the "kick down" point and also as part of its normal gearshift control strategies.
The "drive by wire" nature of the ECM means that the correct operation of the APP sensor is vital to the function of the ECM. It is for this reason that the sensor consists of 2 independent potentiometers. In this way the validity of the signals can easily be checked and fault-handling modes used if any error should be detected.
There are two diagnostic checks on the output signal of this sensor: -
1. A range check where a fault is detected if the signal voltage exceeds a minimum or maximum threshold.
2. A rationality check where the two potentiometer voltages are compared. A fault is detected if the difference is greater than a voltage dependant threshold.
NOTE: The voltage signal from potentiometer 1 is twice that of potentiometer 2
Factory Service Tools
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.