Crankshaft sensor

The crankshaft sensor is one of the key providers of information of the engine control. It detects the speed and position of the crankshaft and forwards this information to the engine control in the form of an electrical signal. On this page, you can find out how crankshaft sensors work, and what must be taken into account when checking them in order to prevent damage.

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 suitably qualified personnel only.

Crankshaft position sensor function

Crankshaft sensor funktion — Operating principle

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.

Checking the crankshaft sensor

Troubleshooting:

The following procedure is recommended for troubleshooting:

Read out the fault memory
Check the electrical connections of the sensor wiring, the connector, and the sensor for correct connection, breaks, and corrosion.

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!

Vehicle electronics, sensors, crankshaft sensor, inductive encoder — Inductive sensor – example OK

Vehicle electronics, sensors, crankshaft sensor, Hall sensor — Hall generator – example OK

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.

Make sure that the distance to the encoder is correct and that the sensor is fitted correctly.

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