Home Sensors Crankshaft Sensor, Crank Angle Sensor or Engine speed sensor
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Sensors
Crankshaft Sensor, Crank Angle Sensor or Engine speed sensor E-mail
The Crankshaft Sensor is used to measure engine speed and Crankshaft position. It can be seen fitted into the block of the engine adjacent to the crankshaft, towards the Flywheel, by the front pulley or inside the distributor.
The crankshaft Sensor is critical to the stating of an engine. A failed sensor will give you a no start situation.
 
  • The Crankshaft sensor is an inductive type sensor. It consists of a magnet and a coil wound around the magnet. It is triggered by reference points passing the sensor tip.

    • The reference points can be pins mounted to the flywheel in the form of a trigger disc or Relucter. These will divide the 360 degrees rotation of the engine into segments that the Engine control can use for The ignition system or  for the start of Injection.

     

  • Each time a reference point passes the tip of the sensor it excites the magnet an ac voltage is then induced in the Coil.The Ac voltage is sent as a signal voltage back to the Engine control Unit.

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  • The Crankshaft sensor or Engine speed sensor will have 2 or 3 pins. The 3rd pin is used for a screen.

    • The screen suppresses any interference.


The Engine Management light will be triggered if the Crankshaft sensor moves outside of normal operating values. 

A fault with this sensor can cause the engine not to start.


Testing with a voltmeter:  Set your voltmeter to Ac Volts. You can connect the probes to the 2 terminals of the sensor. It doent matter which way around as it is alternating current.  If it  is a 3 pin sensor  you need to find which one is the screen. This will usually show continuity to earth when testing with the meter set to  ohms. A cranking Engine will show approximately 0.5 - 1.0 volt. A running engine will show approx 2.5-3.0v volts Ac.

Testing with an Oscilloscope:

 

 

Measurement taken with a Pico Automotive Oscilloscope


The above image shows a reading taken with the engine cranking. You can see in the measurement the TDC point, created by a missing tooth or pin in the flywheel, trigger disc or relucter. 
The Voltage will increase as the engine speed increases. Some Engines such as Renault use 2 reference points. This is often used to create a more distinctive TDC reading for the Ecu. The engine control unit can then have a finer fault tolerance.