Crankshaft sensor - Hall effect

You will require a PicoScope to perform this test. A list of suitable accessories can be found at the bottom of this page.

How to perform the test

  • Plug a BNC test lead into Channel B on the PicoScope.
  • Plug a black clip on the black (negative) plug on the test lead.
  • Fit a Back-pinning Probe onto the colored (positive) plug on the test lead.
  • Probe each of the three connections in turn until you find the Hall effect output, as shown below. (The other two terminals on the sensor are either battery positive voltage or a 5 Volt supply and earth/ground.)

The timebase may need to be altered if the signal is checked at varying engine speeds.

Figure 1 shows the multiplug connection of the crankshaft sensor being probed on a GM/Vauxhall/Opel ECOTEC engine. Although the sensor is located on the front pulley, the multiplug loom connection is located near the air flow sensor.

Example waveform

Waveform notes

The Hall Effect Crankshaft sensor is utilised by many vehicle manufacturers to indicate crankshaft speed and position. These Crankshaft sensors provide a square wave output voltage (either 5 V or 12 V) with a change in frequency relative to engine speed. An increase in engine speed is met with an increase in the output frequency from our Crankshaft sensor. This system should not be confused with the Simtec AC-excited system that uses a frequency-modulated signal.

Technical information

The Crank Angle Sensor (CAS) or Crankshaft Position Sensor (CPS) can be mounted in various locations such as near the front pulley, to the rear of the engine into the flywheel, in the side of the engine block or within the distributor.

The output signal produced is used by the Engine Control Module (ECM) to determine the exact position of the engine.

The Hall effect type of crankshaft sensor is a simple on/off switch that produces a digital output that is recognised and processed by the ECM. The sensor is triggered by a rotating metal disc with openings, the disc passing between the electromagnet and the semiconductor.

A semiconductor has the ability to be a conductor or an insulator depending on the strength of the magnetic field in which it is placed. This magnetic field is switched on and off by the rotating disc that travels between the two objects. A magnetic field that passes through one of the openings will stop the current. When a solid part of the disc is between the two parts of the sensor, the current flows again. This action produces a digital square wave that is understood by the ECM or amplifier, which then does not need the extra circuitry to convert the analogue signal into a digital signal.

The sensor has its characteristic three connections: a supply voltage, an earth and the output signal. The square wave may vary in amplitude when seen on the oscilloscope, but this does not matter as it is the frequency that is important, not the voltage. The output can also be measured on a multimeter that has a frequency function.


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

  • Back-pinning Probe Set


  • Flexible Back-pinning Probe


  • PicoScope Battery Clip


  • Large Dolphin/Gator Clips


  • Premium Test Lead: BNC to 4 mm, 3 m


  • Premium Test Leads: Set of four leads 3 m (TA125 - TA128)


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Guided test: Crankshaft - Hall Effect