Crankshaft sensor - How it works

General points

The task of crankshaft sensors is to determine the speed and position of the crankshaft. They are usually installed on a gear rim near the flywheel. There are two types available: inductive sensors and Hall-type sensors. Before carrying out crankshaft sensor tests it is vital to determine what type of sensor is involved.

How it works

The rotary movement of the gear rim affects changes in the magnetic field. The different voltage signals produced by the magnetic fields are sent to the control unit. The control unit uses the signals to calculate the speed and position of the crankshaft in order to receive important basic data for fuel injection and ignition timing

Effects of failure

The following fault symptoms could be indications of crankshaft sensor failure:
■ Engine misses
■ Engine comes to a standstill
■ A fault code is stored

Causes of failure can be:
■ Internal short-circuits
■ Interrupted cables
■ Cable short-circuit
■ Mechanical damage to the sensor wheel
■ Soiling through metal abrasion

Troubleshooting
■ Read out the fault code
■ Check electrical connections of the sensor cables, the connector and the sensor for correct connection, breaks and corrosion
■ Watch for soiling and damage

Direct testing of the crankshaft sensor can be difficult if it is not known exactly what type of sensor is involved. Before the test it must be established whether it is an inductive or Hall-type sensor. The two types cannot be distinguished from one another on the basis of appearance. Three connector pins do not allow exact assumptions about the respective type involved. The specific manufacturer specifications and the details in the spare parts catalogue will help here. As long as it is not perfectly clear what type of sensor is involved, an ohmmeter must not be used for testing. It could destroy a Hall-type sensor!

If the sensor has a 2-pole connector, it is likely to be an inductive sensor. In this case, intrinsic resistance, a ground connection and the signal can be determined. To do this, remove the pin connection and test the internal resistance of the sensor. If the internal resistance value is between 200 and 1,000 ohm (depending on the reference value) the sensor is OK. If the reading is 0 ohm there is a short-circuit and MOhm indicates a cable interruption. The ground connection test is carried out using the ohmmeter from one connection pin to vehicle ground. The resistance value has to tend towards infinity. The test with an oscilloscope must result in a sinus signal of sufficient amplitude. In the case of a Hall-type sensor only the signal voltage in the form of a rectangular signal and the supply voltage must be checked. The result must be a rectangular signal depending on the engine speed. 

"Once again, please remember: The use of an ohmmeter can destroy a Hall-type sensor"

Installation note

Make sure of the correct distance to the sensor wheel and sensor seat.