Transfer Case Two/Four Wheel Drive Actuator Assembly

WARNING: This page is about a different car, the 2008 GMC Sierra, 2008 GMC Cab & Chassis Sierra, 2008 Chevrolet Silverado, and 2008 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.

Fig 1: Transfer Case Two/Four Wheel Drive Actuator Assembly

Courtesy of GENERAL MOTORS CORP.

The transfer case two/four wheel drive actuator assembly consists of a PM DC motor and gear reduction assembly. It is located on the left side, drivers side, of the transfer case. When activated, it turns the sector shaft of the transfer case clockwise or counter clockwise to shift the transfer case. The encoder motor is controlled by the transfer case shift control module. This circuit consists of a driver on both the motor control A and motor control B circuits. The encoder motor is bi-directional, to allow the motor to shift the transfer case from 2HI or 4HI to NEUTRAL and 4LO positions. The transfer case encoder motor can be fully driven clockwise or counterclockwise using a scan tool. You may also monitor motor control A and B circuits using a scan tool.

The two/four wheel drive actuator assembly also has a built in incremental sensor. This device is a linear encoder. The transfer case shift control module sends a 5 volt reference signal to the encoder. The transfer case shift control module reads the voltage back based on the exact position of the sector shaft of the transfer case. The transfer case shift control module knows if a shift has been completed and if the shift is somewhere in between.

The encoder motor on the MP 1625/1626 does not have an internal brake like the NVG 246. The encoder motor is not serviceable and must be replaced as an assembly.