Electrical Components

WARNING: This page is about a different car, the 2003 GMC Sierra, 2003 GMC Cab & Chassis Sierra, 2003 Chevrolet Silverado, and 2003 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.

Below is a list of major components that make up the automatic transfer case (ATC) system.

Front Axle Actuator: The front axle actuator engages and disengages the front axle. The front axle actuator consists of a permanent magnetic (PM) motor, a worm gear controlled plunger, a front axle switch and an electronic control circuit. When a range shift to 4HI, or 4LO is requested, the transfer case shift control module requests engagement of the front axle by grounding the axle actuator control circuit through a current limiting driver. The front axle actuator also sends a return signal to the TCCM indicating when the 4WD is engaged.

SERVICE Indicator (4WD): The SERVICE indicator (4WD) is an integral part of the cluster and cannot be serviced separately. This indicator is used to inform the driver of malfunctions within the automatic transfer case (ATC) system. The SERVICE indicator (4WD) is controlled by the transfer case shift control module via a Class 2 message or by a service indicator control circuit.

Transfer Case Encoder Motor: The transfer case encoder motor consists of a permanent magnet (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 encoder motor also has a built in encoder. This device is linear encoder This device is a linear encoder for 2003. The TCCM sends a 5 volt reference signal to the encoder. The TCCM reads the voltage back based on the exact position of the sector shaft of the transfer case. The TCCM knows if a shift has been completed and if the shift is somewhere in between. The encoder motor on the NVG 263 does not have an internal brake like the NVG 246. The encoder motor is not serviceable and must be replaced as an assembly.

Transfer Case Shift Control Module (TCCM): The TCCM is new for 2003. The TCCM has been standardized for all K trucks. The TCCM contains the same hardware, boot software, and operational software found in other GM K trucks. The only difference is the calibration file downloaded into the TCCM memory. The TCCM comes with the appropriate calibrations out of the factory, but new calibrations must be flashed into the TCCM during service. This is especially important if a new TCCM is installed during service. Calibration files may be introduced irregularly. See your technical service bulletins. Refer to Transfer Case Control Module Reprogramming .

Vehicle Speed Sensor (VSS): There is a VSS mounted to the transfer case on the rear output shaft. The VSS is a permanent magnet (PM) generator. The PM generator produces a AC voltage. The AC voltage and frequency increases as speed increases. The VSS is an input to the powertrain control module (PCM). The PCM sends this information to the transfer case shift control module via the Class 2 serial data bus.