Accelerator pedal position sensor

The purpose of this test is to evaluate the correct operation of the APP sensor based on the output voltages in relation to the gas pedal position.

Connection Guidance

Connection for diagnostic work will of course vary dependent on application.

Technicians should whenever possible gain access to the test circuit without damage to seals and insulation. If this is not possible then make sure appropriate repairs are completed.

General connection advice;

PicoScope offers a range of options within the test kits.

Dependent on difficulty of access, choose from,

  1. Breakout leads.
  2. Back-pinning probes.

Testing Sensors and Actuators; (to include relevant circuit/connectors).

  • When testing a sensor, it is desirable to gain access at the control unit.
  • When testing an actuator, it is desirable to gain access at the actuator.

How to perform the test

  1. Use the vehicle wiring diagram to identify the two signal circuits from the sensor.
  2. Connect PicoScope Channel A and Channel B to the signal circuits.
  3. Minimise the help page and with the example waveform on your screen PicoScope has already selected suitable scales for you to capture a waveform.
  4. Start the engine and allow it to idle.
  5. Select GO or press the space bar to see live data.
  6. Carry out a WOT test.
  7. With your live waveform on screen select STOP or press the space bar to stop your capture.
  8. Use the WAVEFORM BUFFER and ZOOM tools to examine your waveform.

Example waveform

Waveform notes

In this example, the Accelerator Pedal Position (APP) sensor is of the potentiometer type. It receives two reference voltages from the Powertrain Control Module (PCM), having two ground wires and two signal wires that send a varying voltage back to the PCM relating to accelerator pedal position. The signal voltage sent back to the PCM may vary from manufacturer to manufacturer but will probably never be greater than 5 volts.

Waveform Library

Go to the drop-down menu bar at the lower left corner of the Waveform Library window and select, Accelerator pedal position sensor (analog).

Further Guidance

With the increasing level of electronic control and the subsequent decrease in moving mechanical parts it is inevitable that we will see more items being controlled in a "fly by wire manner".

One example of this is throttle control. The majority of vehicles currently being produced no longer use an accelerator cable but instead use an APP in conjunction with an electronic throttle control actuator (ETC) incorporating an electronic throttle motor and a throttle position sensor (TPS).

The APP is quite simply one or, more commonly, two potentiometers attached to the accelerator pedal. As the accelerator is depressed, a voltage signal is sent to the PCM relaying the actual position of the accelerator pedal and thus the driver's physical demand. As a result of this input, the PCM then generates an output to the relevant actuator; in this case the ETC. As previously mentioned, the APP commonly has two potentiometers. These are employed to act as a plausibility test and also to ensure a degree of failsafe operation.

Several methods are used to generate the signal. The great majority use the common 5 volt reference as is used throughout the engine management system. The two most common methods of signal generation are as follows:

Figure 2: Potentiometer 1 generates a signal of 0.3 to 4.8 volts (red trace in Figure 2) and potentiometer 2 generates a signal of 0.5 to 4.8 volts (blue trace in Figure 2). With an accelerator pedal position of 45 degrees, potentiometer 1 may be outputting a signal of 2 volts and potentiometer 2 a signal of 3 volts, for example.

Figure 3: Potentiometer 1 generates a signal of 0.3 to 4.8 volts (red trace in Figure 3) and potentiometer 2 generates a signal of 4.8 to 0.3 volts (blue trace in Figure 3). With an accelerator pedal position of 0 degrees, potentiometer 1 may output a signal of 0.5 volts and potentiometer 2 may output a signal of 4.5 volts.

Upon receiving signals in this manner the PCM is able to ensure that the information is correct; for example, if APP angle is 45 degrees, then potentiometer 1 outputs 2 volts and potentiometer 2 outputs 3 volts. If there is any deviation from this then the PCM detects a possible fault and logs a relevant fault code. If one potentiometer track should fail then once again the PCM is able to detect this and run in a failsafe or emergency mode, often raising the idle and limiting throttle operation and lighting the malfunction indicator lamp (MIL). The use of two potentiometers also enables the PCM to monitor the speed at which the accelerator is depressed and closed, the throttle position thus controlling fuelling accordingly.

Should you suspect a fault with the signal, test the wiring from the PCM to the APP.

Ensure that the PCM has good power supplies and grounds where required.

Test the APP (disconnected) with an ohmmeter.

Example pin data

Tested from a Smart Forfour 1.1 petrol 2005 MY.
Hella component
6 pin connector

Pin 1= 2.5 V reference voltage (yellow/red)
Pin 2= 5.0 V reference voltage (yellow/green)
Pin 3= Signal voltage, approx 1 V closed throttle & 3.8V open throttle (grey)
Pin 4= 0 V ground (brown/white)
Pin 5= 0 V ground (brown)
Pin 6= Signal voltage, approx 0.5 V closed throttle & 1.8 V open throttle (pink/black)

All figures quoted are approximate and measured by back pinning with ignition on and the multiplug connected.

GT063-4

Disclaimer
This help topic is subject to changes without notification. The information within is carefully checked and considered to be correct. This information is an example of our investigations and findings and is not a definitive procedure. Pico Technology accepts no responsibility for inaccuracies. Each vehicle may be different and require unique test settings.

Suitable accessories

  • Premium 6-way breakout lead set

    £269.00

  • Back-pinning Probe Set

    £40.00

  • Flexible Back-pinning Probe

    £3.00

  • PicoScope Battery Clip

    £2.75

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Guided test: Accelerator Pedal Position Sensor - analog