Shift Motor/Mode Sensor
ASSEMBLY-SHIFT MOTOR/MODE SENSORDESCRIPTION
The shift motor (1) is an electromechanical device consisting of a DC permanent magnet motor, a motor brake, a gear train and an analog position sensor. The shift motors' overall function is to move and lock a gear that moves the mode and range forks found in the transfer case. This allows the transfer case to be shifted electrically to multiple operating positions (4LOCK, AWD, N (neutral), and 4LO). The operating current of the shift motor under stall conditions is 30 amps maximum at 72° F with 13.5 volts, at the motor leads.
The shift motor contains a motor brake, which provides a means of holding the transfer case in a selected position.
OPERATION
Shifting in the transfer case occurs when the shift motor brake is released and a Pulse Width Modulated (PWM) voltage is supplied to the shift motor by the Front Control Module (FCM). A linear analog position sensor located inside the shift motor, provides the FCM with the motors angular, rotational position. With this information, the FCM continuously knows the motors' position, and therefore allows it to accurately control the motors' operation, including voltage polarity which is used to control motor direction.
The brake in the shift motor consists of a solenoid that when energized, allows the shift motor to rotate. During normal operation (vehicle ignition ON), pin 6 on the shift motor connector will have a constant positive battery potential with respect to the vehicles ground. The FCM allows a return current path through Pin 7 when the brake needs to be released and allow the transfer case to shift. The operating current should not be greater than 1.2A when 12Vdc is applied. The motor brake functions as follows:
- The motor brake must always be released while a shift is taking place.
- The motor brake must always be released for a calibrated amount of time before a shift and after a shift. There is an exception for shifts into a NEUTRAL. The motor brake must always be released for a calibrated amount of time before a shift and after the shift for a period of time greater than 2 but less than 5 seconds.
- The motor brake must always be engaged while a Motor Brake DTC is active.