Accelerator Pedal Position Sensor: Description and Operation

Telescoping Rod (Backup Rod):

The accelerator pedal position sensor consists of a variable electrical resistance (potentiometer) and a safety switch. The safety switch is designed as a double contact switch. Both components are activated by the potentiometer gate lever. The control lever is fastened to it. The shaft pivots on the stud next to the potentiometer gate lever. If the ignition switch is in the on position or if the engine is running, the electronic accelerator control unit energizes the potentiometer with a constant reference voltage.


R25 Accelerator pedal position sensor
13 Control lever
16 Gate lever

Control Unit:

Adjustment movement at the accelerator pedal changes the position of the potentiometer through the accelerator linkage, gate and control levers. A variable voltage is sent back to the electronic accelerator control unit, depending on the accelerator pedal position. In the system control portion of the control unit this signal is processed further. If the accelerator pedal is not depressed (idle position), the safety switch of the accelerator pedal position sensor is open. There is voltage on the input side of the safety switch whenever the ignition switch is turned on or with the engine running. The safety switch closes at 4 - 6° above the idle stop.

Fuel Pump Relay:

If the safety switch is closed, then circuit 15 at the fuel pump relay (or Engine Systems Control Unit (MAS)) receives voltage. If the accelerator pedal is moved from wide open throttle in the direction of idle, the safety switch opens at approx. 6 - 4~ before the idle stop. At idle position, voltage for the fuel pump relay or MAS, circuit 15, is supplied by the closed safety switch of the accelerator actuator. The maximum current flow should not exceed 1 amp. The switch is not protected from a short circuit to ground.