Crankshaft position sensor function
Here you will find useful basic information and important tips relating to the crankshaft sensor in vehicles.
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 day-to-day work. The information provided on this website is intended for use by suitably qualified personnel only.
The function of crankshaft sensors is to measure the crankshaft's speed and position. They are most commonly installed near to the flywheel ring gear. There are two designs: Inductive sensors and Hall generators. Before the crankshaft sensor is tested, it is essential to know which type of transmitter is involved.
The rotary movement of the ring gear results in changes to the magnetic field. These generate varying voltage signals in the crankshaft sensor, which are transmitted to the control unit. The control unit uses the signals to calculate speed and position of the crankshaft in order to gain important basic data for injection and ignition timing.
A faulty crankshaft sensor can cause the following symptoms:
Causes of failure can be:
The following procedure is recommended for troubleshooting:
Direct checks on the crankshaft sensor can be difficult if the exact design type of the sensor is not known. Before the checks, it must be clear whether the sensor is an inductive sensor or Hall generator. It is not always possible to distinguish between the two in terms of appearance. If there are three pins on the connector, no precise statements can be made about the respective type. The specific manufacturer specifications and the specifications in the spare-parts catalog provide further assistance here.
If the design type has not been definitively clarified, an ohmmeter must not be used for the tests. The voltage from the measuring device used for the resistance test could destroy a Hall generator!
If the sensor has a 2-pin connector, it is most likely an inductive sensor. In this case it is possible to determine the internal resistance, a potential short circuit to frame, and the signal. To do this, remove the plug connection and check the internal resistance of the sensor. If the internal resistance value is 200 to 1,000 ohms (depending on the reference value), the sensor is OK. If the value is 0 ohms, there is a short circuit, and in the case of M Ohm there is an interruption. The test for a short circuit to frame is carried out using the ohmmeter from a connection pin to vehicle ground. The resistance value must tend toward infinity. The test using an oscilloscope must result in a sinus signal of sufficient strength. In the case of a Hall generator, only the signal voltage in the form of a square wave signal and the supply voltage are to be tested. This must result in a square wave signal depending on the engine speed.
We should warn again at this point that the use of an ohmmeter can destroy the Hall generator.