Throttle switch

Here you will find useful basic information and important tips relating to the throttle valve switch in vehicles.

The throttle valve switch informs the engine control unit about the throttle valve position so that the mixture and ignition can be adjusted to suit the respective load. This page explains how the throttle valve switch works and how a fault impacts the running of the engine. You will also find practical tips on how to check the throttle valve switch.

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

 

HOW THE THROTTLE SWITCH WORKS: FUNCTIONAL PRINCIPLE

Throttle valve switches determine the throttle valve position. They are mounted directly on the throttle valve shaft. The various switch positions are transmitted to the engine management control unit and assist in the calculation of the required fuel quantity.

 

The throttle valve switch houses two switches which are actuated using a switching mechanism. The two switches give the engine management control unit information on the engine operating states "idle" and "full load" to ensure the necessary fuel quantity is accurately calculated.

THROTTLE VALVE SWITCH FAULTY: SYMPTOMS

A faulty throttle valve switch can cause the following:

  • Engine switches off during idle
  • Engine lurches under full load

CAUSES OF A FAULTY THROTTLE SWITCH: CAUSE OF FAILURE

The causes of a faulty throttle valve switch could be:

  • Mechanical damage (e.g. due to vibrations)
  • Contact fault at the electrical connection (corrosion, humidity)
  • Contact fault at the internal switch contacts (humidity, contamination)

CHECKING THE THROTTLE VALVE SWITCH: TROUBLESHOOTING

The following test steps should be considered during troubleshooting:

Check the throttle valve switch

Check the throttle valve switch for correct mounting

Check the switching mechanism

Check whether the switching mechanism is actuated by the throttle valve shaft (with the engine switched off, move the throttle valve from the idle limit stop to the full-load limit stop and listen to hear whether the switches are actuated)

Check the plug connection

Check the plug connection to ensure it is fitted correctly and for any contamination

Check the switch contacts using a multimeter

  • Idle switch closed: Measurement between pin 1 and 3. Measured value = >30 MOhm.
  • Idle switch opened: Measurement between pin 1 and 3 (Caution: Slowly open the throttle valve during the measurement until the idle switch opens). Measured value = 0 ohms.
  • Full-load switch opened: Measurement between pin 1 and 2. Measured value = >30 MOhm.
  • Full-load switch closed: Measurement between pin 1 and 2. Measured value = 0 ohms
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