Throttle position switch

The purpose of this test is to evaluate the correct operation of the throttle switch in response to throttle position.

Connection guidance

Connection for diagnostic work will 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 module.
  • When testing an actuator, it is desirable to gain access at the actuator.

How to perform the test

  1. Use manufacturer data to identify the two switch terminals on the throttle switch unit.
  2. Connect PicoScope channel A and channel B to the switch circuits.
  3. Turn the ignition to on, engine off.
  4. Minimise the help page and with the example waveform on your screen PicoScope has already selected suitable scales for you to capture a waveform.
  5. Start the scope to see live data.
  6. Slowly fully depress and return the throttle pedal to activate the switches.
  7. With your waveforms on screen stop the scope.
  8. Turn the ignition to off.
  9. Use the Waveform Buffer, Zoom and Measuring tools to examine your waveform.

Example waveform

Waveform notes

The Throttle Switch (TS) is invariable a three wire device operating at 5 volts (12 volts on very early systems). The objective of the throttle switch is to inform the Electronic Control Module (ECM) of the position of the throttle movement at throttle housing.
This device can be switched in several ways, so it will be necessary to check with the vehicle and module specific data. Inside the switch there are two sets of contacts, this enables three stages of throttle movement to be monitored.
These are:

  • Throttle closed
  • Throttle part open
  • Throttle fully open (sometimes referred to as wide open throttle - WOT)

The example waveform shows a dual trace picture, monitoring the two switched terminals of the TS. The throttle has been operated from rest to full throttle and back to rest. The blue trace is the idle contact circuit, once the throttle starts operating this switch opens and its voltage changes from 0 to 5 volts. It will remain at 5 volts, even at full throttle, until the throttle is back at its idle position.

The red trace is the full load circuit and is at 5 volts (in its open position) until full throttle is achieved. As the operator only stayed in the full throttle position for a very short period (560 ms) the switch soon opens again and the voltage changes back from 0 to 5.

Waveform Library

Go to the drop-down menu bar at the lower left corner of the Waveform Library window and select, Throttle position switch.

Example throttle position switch.

Further guidance

The throttle switch is a 3 wire twin contact device that is operated by the throttle butterfly spindle. This will provide information to the Electronic Control Module (ECM) for throttle closed, throttle open and wide open throttle position (90% open). When the engine is at tick over the idle contacts are closed, as the throttle is opened these contacts open, sending a signal to the ECM to indicate cruise/part load condition. At the 90% wide open throttle position the other contacts are closed and the signal is sent to the ECM to provide extra fuel enrichment for acceleration.


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


  • Back-pinning Probe Set


  • Flexible Back-pinning Probe


  • Large Dolphin/Gator Clips


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Guided test: Throttle position switch