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Accelerator pedal sensor

Here you will find useful basic information and important tips relating to the accelerator pedal sensor/pedal value transmitter in vehicles.

The accelerator pedal sensor transmits the position of the accelerator pedal to the engine control unit. Based on this information, the load requested by the driver can be implemented immediately. On this page we will explain the principle according to which modern pedal travel transmitters operate, and which symptoms indicate a fault in this sensor. You will also find out how accelerator pedal sensors are checked in the workshop.

Important safety information
The following technical information and practical tips have been compiled by HELLA in order to provide professional support to vehicle workshops in their day-to-day work. The information provided on this website is intended for use by suitably qualified personnel only.

 

HOW THE ACCELERATOR PEDAL SENSOR WORKS: FUNCTIONAL PRINCIPLE

Modern vehicles are being equipped with an ever-increasing number of electronic components. Among other things, this is due to legal regulations, e.g. those governing a reduction in emissions and fuel consumption. Electronic components are also increasingly being used to increase active and passive safety as well as driving comfort. One of the most important components is the accelerator pedal sensor.

 

When it comes to automotive applications, a non-contact sensor based on an inductive principle is increasingly being used. This sensor comprises a stator (which includes an excitation coil, receiver coils, and an electronic evaluation unit) and a rotor (formed of one or more closed conductive loops with a certain geometry).

 

The application of alternating voltage to the transmission coil produces a magnetic field which induces voltages in the receiver coils. A current is also induced in the rotor conductive loops which, in turn, influences the magnetic field of the receiver coils. Voltage amplitudes are produced depending on the position of the rotor relative to the receiver coils in the stator. These are processed in an electronic evaluation unit and then transmitted to the control unit in the form of direct-current voltage. This evaluates the signal and forwards on the relevant pulse, e.g. to the throttle valve actuator. The characteristics of the voltage signal depend on how the accelerator pedal has been pressed.

SYMPTOMS OF A FAULTY ACCELERATOR PEDAL SENSOR: SYMPTOMS

If the accelerator pedal sensor fails, the following fault symptoms may occur:

  • Increased engine idling speed
  • Vehicle does not respond if the accelerator pedal is pressed
  • Vehicle switches to "limp-home mode"
  • Engine warning light in the cockpit illuminates

ACCELERATOR PEDAL SENSOR FAULTY: CAUSE OF FAILURE

A failure could have a number of different causes:

  • Damaged cables or connections on the accelerator pedal sensor
  • Missing voltage and ground supply
  • Faulty electronic evaluation unit in the sensor

CHECKING THE ACCELERATOR PEDAL SENSOR: TROUBLESHOOTING

The following test steps should be considered during troubleshooting:

  • Read out fault code
  • Visual inspection of the accelerator pedal sensor to check for mechanical damage
  • Visual inspection of the relevant electrical connections and cables to ensure they are properly fitted and for any damage
  • Check of the sensor using an oscilloscope and multimeter

 

Using the example of a MB A-Class (150) 1.7, the following test steps, technical data, and figures are listed to explain the troubleshooting work.

Control unit pin Signal Test conditions Reference value
C5 blue-yellow Acceleration off 0V
C5 Acceleration off 4.5 – 5.5 V
C8 violet-yellow Acceleration on 0V
C blue-grey Acceleration on,
accelerator pedal released
0.15V
C9 Acceleration on,
accelerator pedal pressed
2.3V
C10 violet-green Acceleration on,
accelerator pedal released
C10
  Acceleration on,
accelerator pedal pressed
4.66V
C23 brown-white Acceleration on 0V

→ output signal ← input signal ⊥ control unit ground

SIGNAL RECORDING FROM PIN C5

This measurement checks the voltage supply to the sensor. Ignition on/off.

SIGNAL RECORDING FROM PIN C9

Ignition on, press pedal, then release pedal. The signal rises and falls depending on the speed at which the pedal is pressed and released.

SIGNAL RECORDING FROM PIN C10

Ignition on, press pedal, then release pedal. The signal rises and falls depending on the speed at which the pedal is pressed and released.

RECOMMENDATION!

The measurements should be performed by two people. The work involved in capturing the signals on the sensor, carrying out various test cycles, and performing diagnostics work on the oscilloscope is difficult for a single person to handle, and it will take them much longer to complete this work.