Zero-gear sensor, manual transmission

On vehicles with manual transmission, a zero-gear sensor is installed on the top of the transmission housing and has the task of identifying the idle position of the gearshift lever. The zero-gear sensor is a PLCD sensor (PLCD stands for Permanent magnetic Linear Contactless Displacement). The gear shift causes the gearshift rod and therefore the magnet in the transmission to move. The Digital Engine Electronics (DME) identifies the position of the gearshift lever from the PLCD sensor. The following distinctions must be made for the automatic engine start-stop:

• Gear engaged - automatic engine start-stop without function
• Idle position engage - engine starts at 10 % clutch operated
• Gearshift lever pressed lightly - engine starts at 90 % clutch operated.
  Fig 1: Zero-Gear Sensor - Circuit Diagram

  Courtesy of BMW OF NORTH AMERICA, INC.

Teach-in is necessary to compensate for tolerances in the mechanical and electrical systems. The engine control unit then evaluates the maximum ranges in which the engine may start with clutch control as a ratio of the learnt zero point of the gearshift lever. When the clutch pedal is fully operated the engine can start within a gearshift lever articulation of 1.89 mm (10 percent pulse width modulation).

The PLCD sensor is supplied with 5 volts. The output voltage is a pulse-width modulated signal. The duty cycle changes dependent on the position of the gearshift lever (10... 90 percent).

Fig 2: Identifying Zero-Gear Sensor

Courtesy of BMW OF NORTH AMERICA, INC.

The zero-gear sensor must be taught in after replacing the engine control unit. There is a service function to teach in the zero-gear sensor.