Transmission range sensor circuit

The transmission range sensor determines the transmission speed. The transmission control system uses this information to, for example, calculate which gear is required and the shifting time. Scroll through this page and find out about common variants, their functional principle, and how you can check transmission range sensors using simple methods.

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.

How transmission range sensors work

Transmission range sensors record the transmission speed. This information is required by the control unit to regulate the shifting pressure when shifting gears and to decide which gear needs to be engaged at which point.

There are two types of transmission range sensor design: Hall generators and inductive sensors.

The rotation of the ring gear changes the magnetic field, which, in turn, changes the voltage in the transmission range sensor. These voltage signals are forwarded to the control unit by the transmission range sensor.

Checking the transmission range sensor

The following test steps should be considered during troubleshooting:

Check the sensor

Check the sensor for contamination

Check the encoder wheel

Check the encoder wheel for damage

Read out fault memory

Read out the fault memory

Measure the resistance of the inductive sensor using an ohmmeter

Reference value at 80°C: approx. 1,000 ohms.

Check the supply voltage to the Hall generator using a voltmeter

(circuit diagram for pin assignment required).

Attention:
Do not measure the resistance on the Hall generator as doing so could destroy the sensor.

Check the continuity of the sensor's connecting lines between the control unit connector and sensor connector

(circuit diagram for pin assignment required).

Reference value: 0 ohm.

Check the sensor's connecting lines for a short circuit to frame

With the control unit connector pulled out, measure against vehicle ground at the sensor connector using the ohmmeter.

Reference value: >30 MOhm.

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