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Transmission range sensor circuit

Here you will find useful basic information and important tips relating to transmission range sensors in vehicles.

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.

Important safety note
The following technical information and practical tips have been compiled by HELLA in order to provide professional support to vehicle garages in their day-to-day work. The information provided on this website is intended for use by suitably qualified personnel only.

 

HOW TRANSMISSION RANGE SENSORS WORK: FUNCTIONAL PRINCIPLE

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.

TRANSMISSION RANGE SENSOR FAULTY: SYMPTOMS

A faulty transmission range sensor can manifest itself as follows:

  • Failure of the transmission control system, the control unit switches to an emergency program
  • Engine indicator lamp comes on

CAUSES OF FAULTY TRANSMISSION RANGE SENSORS: CAUSE OF FAILURE

Causes of failure can be:

  • Internal short circuits
  • Breaks in wiring
  • Short circuits in wiring
  • Mechanical damage to the encoder wheel
  • Contamination caused by metal abrasion

CHECKING THE TRANSMISSION RANGE SENSOR: TROUBLESHOOTING

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.