Camshaft sensor: Function, fault symptoms and troubleshooting

The camshaft sensor enables the engine control to determine the exact position of the crankshaft drive. This information is required to calculate the ignition point and injection point, among other things. On this page, you can find out how a fault on the camshaft sensor can manifest itself, and which steps should be taken during troubleshooting.

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.

Camshaft position sensor function

The task of the camshaft sensor is to work with the crankshaft sensor to define the exact position of the crankshaft drive. Through the combination of both sensor signals, the engine control unit knows when the first cylinder is in the top dead point.

This information is needed for three purposes:

For the start of injection during sequential injection.
For the actuation signal of the solenoid valve for the pump-nozzle injection system.
For cylinder-selective knocking control.

The camshaft sensor works according to the Hall principle. It scans a ring gear on the camshaft. The rotation of the ring gear changes the Hall voltage of the Hall IC in the sensor head. This change in voltage is transmitted to the control unit and evaluated there in order to establish the required data.

Checking the camshaft position sensor

Check the camshaft sensor: Hall generator OK — Hall generator – example OK

TROUBLESHOOTING:

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

Checking the connection line

Check the connection line from the control unit to the sensor using the ohmmeter. Remove the connector from the control unit and remove the sensor, check the individual cables for continuity. A circuit diagram is required for the pin assignment. Reference value: approx. 0 Ohm.

Checking the connection lines for short circuit to frame

Check the connection lines for short circuit to frame. Measurement between sensor plug and vehicle ground, control unit plug removed. Reference value: >30 MOhm.

Checking the supply voltage

Check the supply voltage from the control unit to the sensor. Insert the control unit plug, switch the ignition on. Reference value: approx. 5 V (note manufacturer's specifications).

Checking the signal voltage

Check the signal voltage. Connect the measuring cable from the oscilloscope and start the engine. A square wave signal must be displayed on the oscilloscope.

Make sure that the distance to the encoder wheel is correct and that the seal fit is correct.

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