Transmission Range Sensor: 7 Complete Quick Facts

Contents: Transmission Range Sensor

What is a transmission range sensor?

Transmission range sensor is used for measuring the gear position, clutch engagement, and speed in a certain transmission system (such as a car). Every transmission range sensing system has a control module or a control unit. The transmission speed is needed by the control unit for regulating the shifting pressure while shifting gears and for deciding which gear requires to be engaged at which point.

transmission range sensor
An automatic transmission cut of a car. Image source: SilverxxxAutomatic transmission cutCC BY-SA 3.0

What are the advantages of the transmission range sensor?

The advantages of transmission range sensor are:

  • It provides precise position control over an entire temperature range.
  • It provides a great degree of freedom for mechanical tolerances without affecting the sensor performance negatively.
  • It comes in a compact size that is easy to integrate.
  • It is not affected by magnetic fields caused by electric motors or power lines.

What is the working principle of transmission range sensors?

The primary function of transmission range sensors is to record the transmission speed. The transmission speed is needed by the control unit for regulating the shifting pressure while shifting gears and for deciding which gear requires to be engaged at which point. A transmission control module or TCM can detect when the clutch is engaged and disengaged. It can also read the RPM. After obtaining all these pieces of information, a TCM performs a certain function based on user feedback. Some TCMs have the ability to store one’s driving habits in internal memory and can apply the memorized information to one’s transmission’s performance.

Ford Escort 1.9 1992 autotrans
An automatic gear selector for automatic transmission. Image source: I, Upior polnocyFord Escort 1.9 1992-autotransCC BY-SA 3.0

Transmission range sensors are generally found in two types of designs: Hall generators and inductive sensors. The ring-gear capapable to change the magnetic-field, and varies the voltage in the transmission range sensor circuit, this receiving voltage signals directed to the control unit thru transmission rangesensor.

Technical data of transmission range sensing devices

Transmission range sensor
Temperature range                            -40 °C to +150 °C
InterfacesAnalog, PWM, SENT
Accuracy≤ +/-1% of the total measuring range over lifetime and temperature
Resolution12 bit
Size90 x 30 x 72 mm.³ (sensor housing.)
ZF Stufenautomatgetriebe 8HP70
Cross-sectional view of a ZF 8HP transmissiontorque converter on the left. planetary gearsets in the center, control mechanisms at the bottom. Image source:http://Ritchyblack – Stefan Krause – Own work 8 Gang Stufenautomatgetriebe der ZF Friedrichshafen AG, Typ:8HP70. Fotografiert am Messestand der ZF-AG bei der Internationalen Automobil Ausstellung 2009. FAL File:ZF Stufenautomatgetriebe 8HP70.jpg
Paddle Shifter 2013 BMW X5 xdrive 35i 9709131265
Paddle shifter (labelled “+”) in a 2013 BMW X5. Image source: Michael SheehanPaddle Shifter – 2013 BMW X5 xdrive 35i (9709131265)CC BY 2.0

What factors can cause a fault in transmission range sensing?

The factors that can cause failure in transmisson range sensing are:

  • Breaks in the wiring system.
  • Certain mechanical damage caused to the encoder wheel.
  • Internal short circuits.
  • Contamination as a result of metal abrasion.
  • Short circuits in wiring.

How can we detect a fault in transmission range sensing?

The symptoms that a faulty transmission range sensing device shows are:

  • The engine indicator light comes on.
  • Decreased engine performance.
  • The vehicle remains stuck in one gear.
  • The control unit shifts to an emergency mode when it detects an error in the functioning of the sensing system.
  • The acceleration might become slow.
  • The transmission might automatically shift to neutral gear without informing beforehand.
  • Improper downshifts might occur while stopping at a traffic light.
  • The user might not be able to shift from neutral gear.
  • The user might get stuck while driving uphill.
  • There might be delayed shifting response from lower gears while accelerating.
  • The torque converter might not function properly.

What should be done to troubleshoot faults in transmission range sensing?

In case of occurrence of any transmission range sensing faults, one should follow the given steps:

  • The sensor should be checked for any kind of contamination.
  • The encoder wheel requires to be checked for any sort of damage.
  • The voltage supply to the hall generator needs to be checked by using a voltmeter and one should never measure the resistance on the Hall generator as this might be cause of sensor damage.
  • The continuity of the transmission sensor’s connecting lines lying between the sensor connector and the control unit connector should be checked (Reference value: 0 ohms).
  • The faulty memory should be readout.
  • The sensor’s connecting lines should be checked for a short circuit to frame (Reference value: \u003e30 MOhm).
  • The resistance of the inductive sensor should be measured with an ohmmeter with a reference value placed at 80°C: approx. 1,000 ohms.

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