Transfer Case - Nvg 263-np1 Chevrolet Cab & Chassis Silverado 3500

Fastener Tightening Specifications

Fastener Tightening Specifications

Capacities - Approximate Fluid

Capacities - Approximate Fluid

Scheme 29

Scheme 30

Scheme 31

Scheme 32

Scheme 33

Scheme 34

Transfer Case Control Connector End Views

Front Axle Actuator Connector Part Information 15324541 4-Way F Metri-Pack 150 Series Sealed (BU) Pin Wire Color Circuit No. Function A BK/WH 1695 Axle Switch Signal B L-BU 1296 Axle Actuator - Control C BN 241 Ignition 3 Voltage E BK 2150 Ground

Transfer Case Shift Control Module - C1 Connector Part Information 12084944 16-Way F Micro-Pack 100 Series (BK) Pin Wire Color Circuit No. Function A1 D-GN/WH 1133 ATC Class 2 Serial Data A2 L-BU 1296 4WD Relay Coil Supply Voltage A3 - - Not Used A4 PU/WH 1565 4 LO Indicator - Control A5 TN/BK 1566 4 HI Indicator - Control A6 L-BU 1693 Switch Signal A7 BK/WH 1554 Encoder Low Reference A8 BK/WH 1851 Ground B1-B2 - - Not Used B3 L-GN/BK 1563 2 HI Indicator - Control B4 BN 1560 Neutral Indicator Control B5 GY/BK 1694 4WD Low Signal B6 BN/WH 1555 Encoder Signal B7-B8 - - Not Used

Transfer Case Shift Control Module - C2 Connector Part Information 12064860 16-Way F Metri-Pack 100 Series (GY) Pin Wire Color Circuit No. Function A1 PU 401 Signal Low - Front A2 YE 400 Signal High - Front A3-A7 - - Not Used A8 L-GN/BK 431 5-Volt Reference B1 L-BU 2221 Signal High - Rear B2 D-GN 2222 Signal Low - Rear B3-B5 - - Not Used B6 BK/WH 1695 4WD Engaged Signal B7 - - Not Used B8 GY 596 5-Volt Reference

Transfer Case Shift Control Module - C3 Connector Part Information 12052856 4-Way F Metri-Pack 280 Series (BK) Pin Wire Color Circuit No. Function A BK 2150 Ground B OG 1640 Battery Positive Voltage C BK 1552 Motor Control A D RD 1553 Motor Control B

Transfer Case Shift Control Switch - C1 Connector Part Information 12064862 8-Way F Metri-Pack 150 Series (BK) Pin Wire Color Circuit No. Function A BK 1050 Ground B - - Not Used C BN 1560 Neutral Indicator Control D - - Not Used E PU/WH 1382 LED Dimming Supply F BN/WH 230 Instrument Panel Lamps Dimming Control G BN 241 Ignition 3 Voltage H GY 596 5-Volt Reference

Transfer Case Shift Control Switch - C2 Connector Part Information 12064860 6-Way F Metri-Pack 150 Series (BK) Pin Wire Color Circuit No. Function A-B - - Not Used C TN/BK 1566 4 HI Indicator - Control D PU/WH 1565 4 LO Indicator - Control E L-GN/BK 1563 2 HI Indicator - Control F L-BU 1693 Switch Signal

Transfer Case Encoder Motor Connector Part Information 15326642 5-Way F GT 280 Series Sealed (BK) Pin Wire Color Circuit No. Function A L-GN/BK 431 5-Volt Reference B BN/WH 1555 Encoder Signal C BK/WH 1554 Encoder Low Reference D BK 1552 Motor Control A E RD 1553 Motor Control B

Diagnostic Starting Point - Transfer Case

Begin the system diagnosis with Diagnostic System Check - Vehicle in Vehicle DTC Information. The Diagnostic System Check - Vehicle in Vehicle DTC Information will provide the following information

1. The identification of the control module or modules which command the system.
2. The ability of the control module or modules to communicate through the serial data circuit.
3. The identification of any stored diagnostic trouble codes (DTCs) and the status of the codes.

The use of the Diagnostic System Check - Vehicle in Vehicle DTC Information will identify the correct procedure for diagnosing the system and where the procedure is located.

Scan Tool Output Controls

Scan Tool Output Controls

Scan Tool Data List

Use the transfer case Scan Tool Data List only after the following is determined

1. The «Diagnostic System Check - Vehicle»(ref-197324-S38390546772005101100000) in Vehicle DTC Information has been completed.
2. There are no diagnostic trouble codes (DTCs) set.
3. Transfer case diagnostic tables indicate the system is functioning properly.

Scan tool values from a properly operating system may be used for comparison with the transfer case system you are diagnosing. The transfer case Scan Tool Data List represents values recorded under the following conditions

1. The engine is at idle.
2. The throttle is closed.
3. The transmission is in PARK or NEUTRAL.
4. The accessories are OFF.
5. The ATC is in 2WD HI.

Only the parameters listed below are referenced in this service manual for use in diagnosis. If all values are within the typical range described below, refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems for further diagnosis.

Scan Tool Data List

Diagnostic Trouble Code (DTC) List

Diagnostic Trouble Code (DTC) List

Circuit Description

The neutral indicator circuit consists of an ignition 3 voltage circuit and a neutral indicator control circuit. When the neutral mode has been selected by the driver, current is supplied to the neutral indicator by the ignition 3 voltage circuit, traveling through the neutral indicator LED at which time the transfer case shift control module supplies the ground through the neutral indicator control circuit. This diagnostic trouble code (DTC) detects an open, a short to ground, or a short to voltage.

DTC Descriptor

This diagnostic procedure supports the following DTC

DTC B0790 Transfer Case Neutral Indicator Circuit Malfunction

Conditions for Running the DTC

1. The ignition is ON.
2. The system voltage is 9-18 volts.

Conditions for Setting the DTC

1. The system monitors the voltage on the neutral indicator control circuit.
2. If the system detects a voltage of 3 volts or less for 1.5 seconds when the neutral indicator is not commanded, the DTC is logged.
3. If the system detects a voltage of 4.5 volts or more when the neutral indicator is commanded, the DTC is logged.

Action Taken When the DTC Sets

The SERVICE 4WD indicator remains illuminated for the remainder of the current ignition cycle.

Conditions for Clearing the DTC

1. The transfer case shift control module will clear the DTC if the condition for setting the DTC is not currently present.
2. A history DTC will clear after 100 consecutive ignition cycles without a fault present.
3. History DTCs can be cleared using a scan tool.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

1. 2: This step inspects for the visual operation of the neutral Indicator. Command both the ON and OFF states.
2. 3: This step tests for voltage at the neutral indicator feed side of the transfer case select switch.
3. 4: This step verifies that the transfer case shift control module is providing ground to the neutral Indicator.
4. 5: This step tests if ground is constantly being applied to the neutral indicator.
5. 6: This step tests the control circuit of the neutral indicator for a short to voltage or an open.
6. 7: This step tests the control circuit of the neutral indicator for a short to ground.

DTC B0790

The range/mode switch circuit consists of 4 modes. The transfer case shift control module supplies 5 volts to the switch through the 5 volt reference circuit. The current travel through the resistor of the currently active mode. The current is then returned to the transfer case shift control module through the switch signal circuit.

The transfer case shift control module constantly monitors this signal voltage to determine the condition of the mode switch circuit.

When each of the modes are selected they complete a circuit through their own specific resistor. The transfer case shift control module continuously monitors the switch input to determine whether the Neutral, 2HI, 4HI, or 4LO mode was selected by the driver.

This diagnostic procedure supports the following DTC

DTC B2725 ATC Mode Switch Circuit Malfunction

1. The ignition is ON.
2. The system voltage is 9-18 volts.

1. The system constantly monitors the voltage on switch signal circuit.
2. If the system detects a voltage level under 0.35 volt or greater than 0.70 volt for 60 seconds, the DTC is logged.

1. All shifting is disabled.
2. The SERVICE 4WD indicator remains illuminated for the remainder of the current ignition cycle.

1. The transfer case shift control module will clear the current DTC if the condition for setting the DTC is not currently present.
2. A history DTC will clear after 100 consecutive ignition cycles without a fault present.
3. History DTCs can be cleared using a scan tool.

The numbers below refer to the step numbers on the diagnostic table.

1. 2: This step tests for proper operation of the transfer case mode select switch.
2. 3: This step tests the mode switch for proper resistance values in all mode switch states.
3. 4: This step tests the switch signal wire for a short to ground, short to voltage, or high resistance

DTC B2725

The transfer case motor is a bi-directional, permanent magnet, D.C. motor. When energized, through motor control A or motor control B, the ground is provided by the opposing motor control circuit and then grounded through the transfer case shift control module ground circuit. The motor, through a series of gears, rotates a shaft which moves the mode and range forks to shift the transfer case between the following ranges

1. 2HI
2. 4HI
3. 4LO
4. Neutral

This DTC detects an open, short to voltage, or short to ground in the motor control A or motor control B circuits, or an open, or short to ground inside the motor.

This diagnostic procedure supports the following DTC

DTC C0306 Motor A or B Circuit Malfunction

1. The ignition is ON.
2. The system voltage is 9-18 volts.

1. The system tests the motor circuits by checking for unwanted voltage.
2. Then, the system supplies voltage on each of the motor circuits and reads the voltage back on the other circuit.
3. If the system detects a condition with the circuits, the DTC is logged. The transfer case shift control module senses a low voltage return in the motor control A or motor control B circuits when a high voltage is expected.
4. The fault must remain current for 30 seconds to set the DTC.

1. All shifting is disabled.
2. The SERVICE 4WD indicator remains illuminated for the remainder of the current ignition cycle.
3. The transfer case shift control module provides a reference voltage of 4.5 volts on the motor A/B line for diagnostic purposes.

1. The transfer case shift control module will clear the DTC if the condition for setting the DTC is not currently present.
2. A history DTC will clear after 100 consecutive ignition cycles without a fault present.
3. History DTCs can be cleared using a scan tool.

The numbers below refer to the step numbers on the diagnostic table.

1. 2: This step tests the battery positive and ground circuits for poor connections.
2. 3: This step tests the encoder motor for an internal short to ground.
3. 4: This step helps isolate motor malfunctions from the transfer case shift control module and wiring.
4. 5: This step test for an open, high resistance, short to ground or short to voltage.

DTC C0306

The transfer case encoder is an analog sensor that returns a signal that represents the physical position of the transfer case sector shaft. This signal represents the mode or range position that the transfer case is currently in. This sensor is made up of the following 3 circuits

1. 5-volt reference circuit
2. Encoder signal circuit
3. Encoder low reference circuit

This DTC detects an out of range reading from the encoder signal or a short to voltage on the 5-volt reference circuit.

This diagnostic procedure supports the following DTC

DTC C0327 Encoder Circuit Malfunction

The transfer case shift control module has a predefined range, 0.5-4.5 volts, in which the encoder feed back should stay within. The DTC sets if the encoder signal feed back falls out of this range.

1. All motor activity stops and the transfer case lock engages.
2. The SERVICE 4WD indicator remains illuminated for the remainder of the current ignition cycle.

1. The transfer case shift control module will clear the DTC if the condition for setting the DTC is not currently present.
2. A history DTC will clear after 100 consecutive ignition cycles without a fault present.
3. History DTCs can be cleared using a scan tool.

The numbers below refer to the step numbers on the diagnostic table.

1. 2: This step checks for a voltage reading on the scan tool.
2. 3: This step tests the encoder circuit for a current malfunction.
3. 4: This step tests for an internal encoder malfunction which is present only in certain areas of the encoder sensor.
4. 5: This step tests for proper reference voltage at the encoder.
5. 6: This step tests the 5-volt reference circuit for proper voltage when the low reference circuit is used as a ground.
6. 8: This step tests the 5-volt reference encoder circuit for a short to voltage, short to ground, an open or high resistance.
7. 9: After determining if the reference voltage measured in Step 4 is correct, Step 6 reviews the reading originally measured in Step 3 to see if it is higher or lower than what is expected. This step helps determine whether the encoder signal circuit is being pulled high or low.
8. 10: This step tests the encoder signal circuit and the encoder low reference circuit for a short to voltage.
9. 11: This step helps determine a faulty encoder.
10. 12: This step tests the encoder signal circuit and the encoder low reference circuit for an open or a short to ground.

DTC C0327

The 4WD low circuit is used to notify either the powertrain control module (PCM) for gasoline applications or the engine control module (ECM) for diesel applications that the vehicle is in 4WD low range. The applicable control module supplies 12 volts to this circuit. The transfer case shift control module grounds this circuit when the vehicle is in 4WD low range.

This DTC detects a short to ground, short to voltage, or an open in the 4WD low circuit.

This diagnostic procedure supports the following DTC

DTC C0359 Four Wheel Drive Low Range (4WD low) Discrete Output Circuit Malfunction

1. The ignition is ON.
2. The system voltage is 9-18 volts.

1. After the transfer case shift control module grounds the output, the 4WD low circuit, and reads back a high voltage, the DTC is set. The system will not attempt setting the DTC again for 5 seconds.
2. The transfer case shift control module reads back a high voltage when a low voltage is expected on the 4WD low circuit.

1. Transmission shift points may be affected.
2. The SERVICE 4WD indicator remains illuminated for the remainder of the current ignition cycle.

1. The transfer case shift control module will clear the DTC if the condition for setting the DTC is not currently present.
2. A history DTC will clear after 100 consecutive ignition cycles without a fault present.
3. History DTCs can be cleared using a scan tool.

The numbers below refer to the step numbers on the diagnostic table.

1. 2: This step tests for proper reference voltage to the transfer case shift control module on the 4WD low circuit.
2. 3: This step tests the 4WD low circuit for a short to voltage.
3. 4: This step tests the 4WD low circuit for an open or high resistance.
4. 5: This step repairs the 4WD low circuit for a short to voltage.

DTC C0359

The front axle control circuit consists of an electric motor actuator which engages and disengages the front axle. The front axle actuator motor consists of a permanent magnetic motor, a worm gear controlled plunger, a front axle switch and an electronic control circuit within the actuator assembly.

The front axle actuator consists of the following circuits

1. The front axle control circuit, which is also connected to the transfer case shift control module
2. The front axle switch circuit, which is also connected to the transfer case shift control module
3. An ignition 3 voltage circuit
4. A ground circuit

When a shift to 2WD, 4HI, or 4LO is requested, the transfer case shift control module engages the front axle by grounding the front axle control circuit through a current limiting driver.

This DTC detects a short to ground, short to voltage or an open circuit.

This diagnostic procedure supports the following DTC

DTC C0379 Front Axle System Malfunction

1. The ignition is ON.
2. The system voltage is 9-18 volts.

1. The transfer case shift control module monitors the state of the front axle switch. The transfer case shift control module reads back the front axle switch circuit for a high and low voltage. The DTC sets if this circuit is high when a low voltage is present or when the circuit is low when a high voltage is present for 10 seconds.
2. The DTC sets if this circuit is high when a low voltage is present or when the circuit is low when a high voltage is present for 10 seconds.

The SERVICE 4WD indicator remains illuminated for the remainder of the current ignition cycle.

1. The transfer case shift control module will clear the DTC if the condition for setting the DTC is not currently present.
2. A history DTC will clear after 100 consecutive ignition cycle without a fault present.
3. History DTCs can be cleared using a scan tool.

The numbers below refer to the step numbers on the diagnostic table.

1. 2: This step tests the front axle circuit for a current malfunction.
2. 3: This step helps determine if the failure is the result of a short to voltage or ground.
3. 4: This step helps determine if the front axle control circuit is shorted to ground.
4. 5: This step tests the integrity of the front axle switch and the ignition 3 voltage circuits.
5. 6: This step tests the front axle control circuit for short to ground.
6. 7: This step tests the front axle control circuit for short to voltage or ground.
7. 8: This step tests the front axle switch signal circuit for a short to voltage.
8. 9: This step tests the front axle ignition 3 voltage circuit and the front axle switch circuit for an open or short to ground.
9. 10: This step tests the front axle control circuit and the front axle ground circuit for an open or high resistance.

DTC C0379

At each power-up, the transfer case shift control module runs a self-test on the following functions

1. EEPROM Checksum
2. ROM Checksum
3. RAM Checksum
4. RAM Malfunction

This diagnostic procedure supports the following DTC

DTC C0550 ECU Malfunction

1. The ignition is ON.
2. The system voltage is 9-18 volts.

1. Critical operational parameters stored in EEPROM have failed Checksum test indicating invalid data.
2. Masked ROM code has failed Checksum test indicating that masked ROM data is not currently valid.
3. ROM code has failed Checksum test indicating that ROM data is not currently valid.
4. One or more RAM locations have failed operational test indicating that some portions of RAM are not functional.

1. The SERVICE 4WD indicator remains illuminated for the remainder of the current ignition cycle.
2. The transfer case control switch does not display the current position LED while DTC C0550 is current.

1. Replace the transfer case shift control module.
2. Perform the «Diagnostic System Check - Vehicle»(ref-197324-S38390546772005101100000) in Vehicle DTC Information.

The number below refers to the step number on the diagnostic table

1. 2: This step replaces the transfer case shift control module.

DTC C0550

Symptoms - Transfer Case

1. Review the system operation in order to familiarize yourself with the system functions. Refer to «Transfer Case Description and Operation»(/chevrolet/cab-chassis-silverado-3500/2004-2007/remont/transfer-case/#transfer-case-nvg-263-np1) .
2. Inspect the easily accessible or visible system components for obvious damage or conditions which could cause the symptom.
3. Inspect the automatic transfer case for the proper fluid level.

Intermittent

Faulty electrical connections or wiring may be the cause of intermittent conditions. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems. Some symptoms may be caused by loose wiring. Be sure to test the system after moving or connecting harnesses, but before replacing parts.

Symptom List

Refer to a symptom diagnostic procedure from the following list in order to diagnose the symptom

1. «Front Axle Will Not Engage»(/chevrolet/cab-chassis-silverado-3500/2004-2007/remont/transfer-case/#transfer-case-nvg-263-np1)
2. «Front Axle Will Not Disengage»(/chevrolet/cab-chassis-silverado-3500/2004-2007/remont/transfer-case/#transfer-case-nvg-263-np1)
3. «Transfer Case Shift Control Switch Inoperative»(/chevrolet/cab-chassis-silverado-3500/2004-2007/remont/transfer-case/#transfer-case-nvg-263-np1)
4. «Service Indicator Always On»(/chevrolet/cab-chassis-silverado-3500/2004-2007/remont/transfer-case/#transfer-case-nvg-263-np1)
5. «Service Indicator Inoperative»(/chevrolet/cab-chassis-silverado-3500/2004-2007/remont/transfer-case/#transfer-case-nvg-263-np1)
6. «Transfer Case Shift Control Switch Indicator Always On - Two or More»(/chevrolet/cab-chassis-silverado-3500/2004-2007/remont/transfer-case/#transfer-case-nvg-263-np1)
7. «Transfer Case Shift Control Switch Indicator Flashes, then Returns to Previous Mode»(/chevrolet/cab-chassis-silverado-3500/2004-2007/remont/transfer-case/#transfer-case-nvg-263-np1)
8. «Transfer Case Shift Control Switch Indicators Flash Continuously 15 Seconds or More»(/chevrolet/cab-chassis-silverado-3500/2004-2007/remont/transfer-case/#transfer-case-nvg-263-np1)
9. «Transfer Case Shift Control Switch Indicator Inoperative - One or More»(/chevrolet/cab-chassis-silverado-3500/2004-2007/remont/transfer-case/#transfer-case-nvg-263-np1)
10. «Transfer Case Will Not Shift»(/chevrolet/cab-chassis-silverado-3500/2004-2007/remont/transfer-case/#transfer-case-nvg-263-np1__transfer-case-will-not-shift)
11. «Transfer Case Popping Noise»(/chevrolet/cab-chassis-silverado-3500/2004-2007/remont/transfer-case/#transfer-case-nvg-263-np1__transfer-case-popping-noise)
12. «Transfer Case Whine or Rumble Noise»(/chevrolet/cab-chassis-silverado-3500/2004-2007/remont/transfer-case/#transfer-case-nvg-263-np1__transfer-case-whine-or-rumble-noise)
13. «Transfer Case Growl or Grinding Noise»(/chevrolet/cab-chassis-silverado-3500/2004-2007/remont/transfer-case/#transfer-case-nvg-263-np1__transfer-case-growl-or-grinding-noise)
14. «Transfer Case Clunk in 2HI Only»(/chevrolet/cab-chassis-silverado-3500/2004-2007/remont/transfer-case/#transfer-case-nvg-263-np1__transfer-case-clunk-in-2hi-only)
15. «Transfer Case Clunk in 4HI»(/chevrolet/cab-chassis-silverado-3500/2004-2007/remont/transfer-case/#transfer-case-nvg-263-np1__transfer-case-clunk-in-4hi)
16. «Transfer Case Clunk in 4LO»(/chevrolet/cab-chassis-silverado-3500/2004-2007/remont/transfer-case/#transfer-case-nvg-263-np1__transfer-case-clunk-in-4lo)
17. «Transfer Case Shudder or Binding»(/chevrolet/cab-chassis-silverado-3500/2004-2007/remont/transfer-case/#transfer-case-nvg-263-np1__transfer-case-shudder-or-binding)
18. «Transfer Case Jumps Out of Gear»(/chevrolet/cab-chassis-silverado-3500/2004-2007/remont/transfer-case/#transfer-case-nvg-263-np1__transfer-case-jumps-out-of-gear)
19. «Transfer Case Leak Diagnosis»(/chevrolet/cab-chassis-silverado-3500/2004-2007/remont/transfer-case/#transfer-case-nvg-263-np1__transfer-case-leak-diagnosis)

The front axle control circuit consists of an electric motor actuator which engages and disengages the front axle. The front axle actuator motor consists of a permanent magnetic motor, a worm gear controlled plunger, a front axle switch and an electronic control circuit all within the actuator assembly.

The front axle actuator consists of the following circuits

1. The front axle control circuit, which is also connected to the transfer case shift control module
2. The front axle switch circuit, which is also connected to the transfer case shift control module
3. A battery feed circuit
4. A ground circuit

When a shift to 4HI or 4LO is requested, the transfer case shift control module engages the front axle by grounding the front axle control circuit through a current limiting driver.

The numbers below refer to the step numbers on the diagnostic table.

1. 2: This step tests the electrical function of the front axle actuator and helps determine mechanical and electrical malfunctions.
2. 3: This step tests for proper power and ground at the front axle actuator.
3. 4: This step tests the operation of the front axle control circuit.
4. 5: This step helps determine if the transfer case shift control module is able to monitor the front axle switch.
5. 6: This step tests the front axle switch circuit for an open or high resistance.
6. 7: This step measures the voltage between the front axle feed circuit and ground.
7. 8: This step tests the front axle control circuit for an open or high resistance.
8. 9: This step inspects the front axle for a mechanical malfunction.
9. 10: This step tests for open fuse in the front axle feed circuit.

Front Axle Will Not Engage

The front axle control circuit consists of an electric motor actuator which engages and disengages the front axle. The front axle actuator motor consists of a permanent magnetic motor, a worm gear controlled plunger, a front axle switch and an electronic control circuit all within the actuator assembly.

The front axle actuator consists of the following circuits

1. The front axle control circuit, which is also connected to the transfer case shift control module
2. The front axle switch circuit, which is also connected to the transfer case shift control module
3. A battery feed circuit
4. A ground circuit

When a shift to 4HI or 4LO is requested, the transfer case shift control module engages the front axle by grounding the front axle control circuit through a current limiting driver.

The numbers below refer to the step numbers on the diagnostic table.

1. 2: This step tests the electrical function of the front axle actuator and helps determine mechanical and electrical malfunctions.
2. 3: This step tests for proper voltage and ground at the front axle actuator.
3. 4: This step tests the operation of the front axle actuator control circuit.
4. 5: This step tests the electrical function of the front axle actuator control circuit.
5. 6: This step tests for proper supply voltage to the front axle actuator.
6. 7: This step tests for open fuse in the ignition 3 voltage circuit.
7. 8: This step tests the front axle actuator control circuit for an open or high resistance.
8. 9: This step tests the front axle actuator signal circuit for an open or high resistance.
9. 10: This step helps determine if the front axle actuator has a mechanical malfunction.
10. 11: This step tests the front axle switch circuit for a short to voltage.
11. 12: This step inspects the front axle for a mechanical malfunction.

Front Axle Will Not Disengage

The range/mode switch circuit consists of the following 4 switches

1. 2HI
2. 4HI
3. 4LO
4. Neutral

The transfer case shift control module supplies a regulated 5 volts, DC, to the switch through the 5 volt regulator circuit. The current travel through the resistor of the currently active switch. The switch then returns current to the transfer case shift control module through the switch signal circuit.

The transfer case shift control module constantly monitors this signal voltage to determine the condition of the mode switch circuit.

When each switch is depressed, the switch completes a circuit through the respective resistor. The transfer case shift control module continuously monitors the switch input to determine which of the following buttons were selected by the driver

1. 2HI
2. 4HI
3. 4LO

The numbers below refer to the step numbers on the diagnostic table.

1. 2: This step tests the functionality of the mode switch.
2. 3: This step tests the modules ability to operate the transfer case modes.

Transfer Case Shift Control Switch Inoperative

The SERVICE 4WD indicator is located in the instrument panel cluster (IPC), and shares the common power and ground of the IPC. The transfer case shift control module controls the service indicator by sending the IPC a Class 2 message. This indicator may be controlled with the scan tool using the IPC device controls.

The number below refers to the step number on the diagnostic table.

1. 2: This step determines whether the failure is the result of a malfunctioning transfer case shift control module or the IPC.

Service Indicator Always On

The SERVICE 4WD indicator is located in the instrument panel cluster (IPC), and shares the common power and ground of the IPC. The transfer case shift control module controls the service indicator lamp by sending the IPC a Class 2 message. This lamp may be controlled with the scan tool using the IPC device controls.

The number below refers to the step number on the diagnostic table.

1. 2: This step determines whether the failure is the result of a faulty transfer case shift control module or the IPC.

Service Indicator Inoperative

The indicator lamps circuit consist of 4 individual lamps contained inside the mode/range switch assembly. The following lamps are contained inside their respective range button

1. 2HI
2. 4HI
3. 4LO
4. Neutral

When the ignition in ON, the transfer case shift control module illuminates the indicator that corresponds to the current transfer case gear position by providing a ground through a current limiting driver.

The transfer case shift control module flashes each indicator lamp after a shift has been requested, and continues to flash until the transfer case shift control module can complete the shift.

A solid state circuit located inside the switch supplies ignition voltage to the lamps. The solid state circuit also receives voltage when the headlamp switch is in the parklamp or headlamp position. When the solid state circuit receives voltage from the headlamp switch, the switch reduces the voltage supplied to the indicator lamps, dimming the lamps when the headlamps are ON.

The numbers below refer to the step numbers on the diagnostic table.

1. 2: This step tests the transfer case electrical control of the lamp circuits.
2. 3: This step helps determine if there is a short to ground in the suspect indicator control circuits.

Transfer Case Shift Control Switch Indicator Always On - Two or More

The transfer case motor is a bi-directional, permanent magnet, DC motor. When energized through motor control A or motor control B, the ground is provided by the opposing motor control circuit and then grounded through the transfer case shift control module ground circuit. The motor, through a series of gears, rotates a shaft which moves the mode and range forks to shift the transfer case between the ranges of 4HI, 2HI, Neutral (N) and 4LO.

If motor control A and B circuits are shorted together, or a motor control driver is damaged in the transfer case shift control module, the transfer case shift control module goes into a shift block mode. The transfer case module also goes into shift block mode if there is a mechanical concern, causing the shift lever detent shaft to bind, or if the transfer case shift control module is not seeing a signal from the park/neutral position (PNP) switch. The shift block mode causes the mode indicator to flash for a period of time when another mode is selected. After that period of time has ended, the indicator reverts back to the previous mode selection.

The numbers below refer to the step numbers on the diagnostic table.

1. 2: This step helps to determine if the transfer case shift control module has the ability to command the encoder motor.
2. 3: This step determines if motor control A and motor control B circuits being shorted together is causing a shift block.
3. 4: This step determines if the motor control A and motor control B circuits are shorted together within the module.
4. 5: This step determines if a binding shift lever detent shaft is causing a shift block.
5. 6: This step has the transfer case removed and repaired.
6. 7: This step determines if the PNP switch is sending the correct range signal.
7. 8: This step replaces the transfer case shift control module.

Transfer Case Shift Control Switch Indicator Flashes, then Returns to Previous Mode

This symptom is usually the result of actions expected to take place during the transition of a transfer case mode change, which has not happened. When the transfer case changes from 2WD to 4WD, for example, the front axle is Locked by the transfer case shift control module. If the transfer case shift control module does not sense that the front axle is applied, the module waits for the action to take place before the gear change is made. While waiting, the mode switch lamp continues to flash for a period of time, at which time all other mode requests are ignored for the duration of the ignition cycle.

The front axle control circuit consists of an electric motor actuator which engages and disengages the front axle. The front axle actuator motor consists of the following components contained within the actuator assembly

1. A permanent magnetic motor
2. A worm gear controlled plunger
3. A front axle switch
4. An electronic control circuit

The front axle actuator consists of the following circuits

1. The front axle control circuit, which is also connected to the transfer case shift control module
2. The front axle switch circuit, which is also connected to the transfer case shift control module
3. A battery feed circuit
4. A ground circuit

When a shift to AUTO 4WD, 4HI, or 4LO is requested, the transfer case shift control module engages the front axle by grounding the front axle control circuit through a current limiting driver.

The numbers below refer to the step numbers on the diagnostic table.

1. 2: This step determines the position of the front axle switch.
2. 3: This step helps determine if the front axle will not engage.
3. 4: This step helps determine if the front axle will not disengage.

Transfer Case Shift Control Switch Indicators Flash Continuously 15 Seconds or More

The indicator lamps circuit consist of 4 individual lamps contained inside the mode/range switch assembly. The following lamps are contained inside the respective range button

1. 2HI
2. 4HI
3. 4LO
4. Neutral

Each time the ignition is cycled, all 4 mode indicators light simultaneously as an indicator check, to ensure proper operation of the indicators. When the ignition is ON, the transfer case shift control module illuminates the indicator lamp that corresponds to the current transfer case gear position by providing a ground through a current limiting driver.

The transfer case shift control module flashes each indicator lamp after a shift has been requested, and continues to flash until the transfer case shift control module completes the shift.

A solid state circuit located inside the switch supplies ignition voltage to the lamps. The solid state circuit also receives voltage when the headlamp switch is in the parklamp or headlamp position. When the solid state circuit receives voltage from the headlamp switch, the circuit reduces the voltage that is supplied to the indicator lamps, dimming the lamps when the headlamps are ON.

The numbers below refer to the step numbers on the diagnostic table.

1. 2: This step tests the transfer case electrical control of the lamp circuits.
2. 3: This step helps determine module failures.
3. 4: This step tests the affected indicator control circuit for an open or high resistance.
4. 5: This step tests the LED dimming supply circuit for an open or short to ground.

Transfer Case Shift Control Switch Indicator Inoperative - One or More

Transfer Case Will Not Shift

Transfer Case Will Not Shift

Transfer Case Popping Noise

Transfer Case Popping Noise

Transfer Case Whine or Rumble Noise

Transfer Case Whine or Rumble Noise

Transfer Case Growl or Grinding Noise

Transfer Case Growl or Grinding Noise

Transfer Case Clunk in 2HI Only

Transfer Case Clunk in 2HI Only

Transfer Case Clunk in 4HI

Transfer Case Clunk in 4HI

Transfer Case Clunk in 4LO

Transfer Case Clunk in 4LO

Transfer Case Shudder or Binding

Transfer Case Shudder or Binding

Transfer Case Jumps Out of Gear

Transfer Case Jumps Out of Gear

Transfer Case Leak Diagnosis

Transfer Case Leak Diagnosis

Removal Procedure

1. Raise and suitably support the vehicle. Refer to «Lifting and Jacking the Vehicle»(ref-197364-S02039416942005101100000) in General Information.
2. Remove the transfer case shield bolts, if equipped.
3. Remove the transfer case shield, if equipped.

Installation Procedure

1. Position the transfer case shield to the crossmember, if equipped.
2. Install the transfer case shield bolts, if equipped. Tighten: Tighten the bolts to 20 N.m (15 lb ft).
3. Lower the vehicle.

1. Remove the transfer case shield, if equipped. Refer to «Transfer Case Fluid Replacement»(/chevrolet/cab-chassis-silverado-3500/2004-2007/remont/transfer-case/#transfer-case-nvg-261-np2) .
2. Remove the fill plug.
3. Remove the drain plug.

Note. Refer to Fastener Notice in Cautions and Notices.

1. Install the drain plug. Tighten: Tighten the plug to 20 N.m (15 lb ft).
2. Fill the transfer case to the bottom of the fill plug hole with the approved fluid.
3. Install the fill plug. Tighten: Tighten the plug to 20 N.m (15 lb ft).
4. Lower the vehicle.

1. Remove the transfer case shield, if equipped. Refer to «Transfer Case Shield Replacement»(/chevrolet/cab-chassis-silverado-3500/2004-2007/remont/transfer-case/#transfer-case-nvg-263-np1) .
2. Remove the front propeller shaft. Refer to «Propeller Shaft Replacement - Front»(ref-197434-S11772894682005101100000) in Propeller Shaft.
3. Disconnect the encoder motor electrical connector.
4. Remove the encoder motor bolts.
5. Remove the encoder motor.
6. Remove the actuator insulator gasket.
7. If replacing the encoder motor, remove the locating pins from the old motor.

1. Install the locating pins to the NEW encoder motor.
2. Position a NEW actuator insulator gasket to the transfer case.
3. Install the encoder motor. NOTE: Refer to «Fastener Notice»(ref-197335-S17275608472005101100000) in Cautions and Notices.
4. Install encoder motor bolts. Tighten: Tighten the bolts, in the sequence shown, to 20 N.m (15 lb ft).
5. Connect the encoder motor electrical connector. Ensure that the retention clips activate.
6. Install the front propeller shaft. Refer to «Propeller Shaft Replacement - Front»(ref-197434-S11772894682005101100000) in Propeller Shaft.
7. Install the transfer case shield, if equipped. Refer to «Transfer Case Shield Replacement»(/chevrolet/cab-chassis-silverado-3500/2004-2007/remont/transfer-case/#transfer-case-nvg-263-np1) .

1. Remove the encoder motor. Refer to «Transfer Case Encoder Motor Replacement»(/chevrolet/cab-chassis-silverado-3500/2004-2007/remont/transfer-case/#transfer-case-nvg-263-np1) .
2. Place the encoder motor on a clean work bench
3. Remove the 2 screws (2) from the motor cover.
4. Remove the 2 screws (1) from the casting.
5. Remove the cover.
6. Remove and save the shim on the output gear.
7. Remove and discard the orange rubber seal from the cover.
8. Remove the output gear (1).
9. Disassemble the harness connector (1) from the encoder.
10. Remove the encoder from the output shaft using a flat tip screwdriver.

1. Assemble the harness to the NEW encoder with the connector legend "TOP" (1) and the encoder part number facing up.
2. Assemble the output shaft into the encoder, being sure to align the encoder tab with the groove on the shaft.
3. Ensure the encoder is seating properly on the output gear.
4. Place the output shaft/encoder on the casting.
5. Place the grommet harness on the casting slot, the flat area on the grommet will be facing up.
6. With the output gear/encoder assembly in hand, carefully align the casting and output gear timing marks (1).
7. At the same time, be sure to align the encoder phasing post (1) with the phasing slot (2) in the casting and insert the shaft into the bushing.
8. Verify that the output gear and idler are engaged properly.
9. Seat the harness wires on the casting channel.
10. Place the shim on the output shaft gear.
11. Press a NEW seal into the cover.
12. Install the cover.
13. Install 2 NEW screws (1) to the casting. Tighten: Tighten the screws to 2 N.m (18 lb in).
14. Install 2 NEW longer screws (2) to the motor cover. Tighten: Tighten the screws to 3 N.m (26 lb in).
15. Install the encoder motor. Refer to «Transfer Case Encoder Motor Replacement»(/chevrolet/cab-chassis-silverado-3500/2004-2007/remont/transfer-case/#transfer-case-nvg-263-np1) .

1. Raise and suitably support the vehicle. Refer to «Lifting and Jacking the Vehicle»(ref-197364-S02039416942005101100000) in General Information.
2. Disconnect the speed sensor electrical connector.
3. Remove the speed sensor.

1. Install the speed sensor. Tighten: Tighten the sensor to 15 N.m (11 lb ft).
2. Connect the speed sensor electrical connector.
3. Lower the vehicle.

1. Disconnect the shift control module electrical connectors.
2. Unsnap and remove the shift control module from the bracket.

1. If a NEW control module is being installed, program the new module. Refer to «Control Module References»(ref-197326-S18267990112005101100000) in Computer/Integrating Systems.
2. Install the shift control module to the bracket.
3. Connect the shift control module electrical connectors.
4. Start the engine and test the automatic transfer case system for proper shift operation.

1. Remove the instrument panel (IP) cluster bezel. Refer to «Bezel Replacement - Instrument Panel (I/P) Cluster»(ref-197333-S15825470872005101100000) in Instrument Panel, Gages, and Console.
2. Pull the tabs on the side of the transfer case driver control switch out.
3. Pull the transfer case driver control switch straight out from the panel.

1. Install the transfer case driver control switch into the instrument panel.
2. Install the IP cluster bezel. Refer to «Bezel Replacement - Instrument Panel (I/P) Cluster»(ref-197333-S15825470872005101100000) in Instrument Panel, Gages, and Console.

Transfer Case Output Shaft Seal Replacement - Front

Tools Required

1. J 8092 Driver Handle
2. J 43484 Output Shaft Seal Installer

1. Remove the transfer case shield, if equipped. Refer to «Transfer Case Shield Replacement»(/chevrolet/cab-chassis-silverado-3500/2004-2007/remont/transfer-case/#transfer-case-nvg-263-np1) .
2. Remove the front propeller shaft. Refer to «Propeller Shaft Replacement - Front»(ref-197434-S11772894682005101100000) in Propeller Shaft.
3. Insert a flat-tipped screwdriver into the inner race.
4. Pry the inner race back.
5. Insert a small pry bar into the inner race.
6. Remove the inner part of the seal.
7. Insert a flat-tipped screwdriver or small pry bar in the space between the outer race of the seal and the transfer case.
8. Remove the outer part of the seal.

1. Install the J 43484 (2) to the J 8092 (1).
2. Install the seal onto the J 43484 (2).
3. Using the J 43484 (2) and the J 8092 (1), install the seal.
4. Install the front propeller shaft. Refer to «Propeller Shaft Replacement - Front»(ref-197434-S11772894682005101100000) in Propeller Shaft.
5. Check the fluid level, add fluid if necessary.
6. Install the transfer case shield, if equipped. Refer to «Transfer Case Fluid Replacement»(/chevrolet/cab-chassis-silverado-3500/2004-2007/remont/transfer-case/#transfer-case-nvg-263-np1) .

Transfer Case Output Shaft Seal Replacement - Rear

Tools Required

1. J 37668-A Seal Installer
2. J 45380 Transfer Case Rear Bushing Remover and Installer

1. Remove the transfer case shield, if equipped. Refer to «Transfer Case Shield Replacement»(/chevrolet/cab-chassis-silverado-3500/2004-2007/remont/transfer-case/#transfer-case-nvg-263-np1) .
2. Remove the rear propeller shaft. Refer to «Propeller Shaft Replacement - One Piece»(ref-197434-S01803903062005101100000) or «Propeller Shaft Replacement - Two Piece»(ref-197434-S21627766012005101100000) in Propeller Shaft.
3. Remove the rear output shaft seal.
4. Inspect the rear output shaft bushing for scoring or wear.
5. Remove the rear output shaft bushing if required, using the J 45380 . Install the finger section of the J 45380 in front of the bushing. Install the tube and forcing screw to the finger section. Ensure the forcing screw is backed out. Using a wrench on the forcing screw, remove the rear output shaft bushing.

1. Install a NEW rear output shaft bushing, if required using the J 45380 Install the bushing or the finger section of the J 45380 . Install the finger section to the main body of the J 45380 . Position the bushing and tool to the case. Using a hammer and the J 45380 , install the bushing.
2. Using the J 37668-A , install the rear output shaft seal.
3. Install the rear propeller shaft. Refer to «Propeller Shaft Replacement - One Piece»(ref-197434-S01803903062005101100000) or «Propeller Shaft Replacement - Two Piece»(ref-197434-S21627766012005101100000) in Propeller Shaft.
4. Check the fluid level, add fluid if necessary.
5. Install the transfer case shield, if necessary. Refer to «Transfer Case Fluid Replacement»(/chevrolet/cab-chassis-silverado-3500/2004-2007/remont/transfer-case/#transfer-case-nvg-263-np1) .

1. Remove the transfer case shield, if equipped. Refer to «Transfer Case Shield Replacement»(/chevrolet/cab-chassis-silverado-3500/2004-2007/remont/transfer-case/#transfer-case-nvg-263-np1) .
2. Drain the transfer case of fluid.
3. Remove the front propeller shaft. Refer to «Propeller Shaft Replacement - Front»(ref-197434-S11772894682005101100000) in Propeller Shaft.
4. Remove the rear propeller shaft. Refer to «Propeller Shaft Replacement - One Piece»(ref-197434-S01803903062005101100000) or «Propeller Shaft Replacement - Two Piece»(ref-197434-S21627766012005101100000) in Propeller Shaft.
5. Remove the transmission shift control cable clip from the transfer case.
6. Remove the transmission vent hose clip from the bracket, if equipped.
7. Disconnect the speed sensor electrical connector.
8. Disconnect the inline to engine harness electrical connector.
9. Remove the inline connector from the harness bracket.
10. Disconnect the encoder motor electrical connector.
11. Remove the clips from the transfer case brackets.
12. Disconnect the transfer case vent hose.
13. Support the transmission with a suitable transmission jack stand.
14. Remove the transmission mount nuts.
15. Remove the crossmember bolts.
16. Remove the crossmember.
17. Remove the transmission mount bolts
18. Remove the transmission mount from the adapter.
19. Support the transfer case with a suitable jack stand.
20. Remove the transfer case adapter nuts.
21. Remove the harness bracket. IMPORTANT: The following service procedure must be performed with the assistance from another technician.
22. Remove the transfer case, perform the following: Slide the transfer case straight back toward the rear of the vehicle. Rotate the transfer case so that the front output shaft is above the torsion bar bracket. Rotate the transfer case (with the input shaft slightly lowered) so that the transfer case is parallel to the torsion bar bracket. Lower the transfer case.

1. Install the transfer case, perform the following: Raise the transfer case into position (the transfer case should be parallel to the torsion bar bracket). Rotate the transfer case so that it is in line with the adapter. Install the transfer case to the adapter. NOTE: Refer to «Fastener Notice»(ref-197335-S17275608472005101100000) in Cautions and Notices.
2. Install the transfer case adapter nuts. Tighten: Tighten the nuts to 50 N.m (37 lb ft).
3. Install the transmission mount.
4. Install the transmission mount bolts. Tighten: Tighten the bolts to 47 N.m (35 lb ft).
5. Install the crossmember.
6. Install the crossmember bolts. Tighten: Tighten the bolts to 70 N.m (52 lb ft).
7. Lower the transmission/transfer case.
8. Install the transmission mount nuts. Tighten: Tighten the nuts to 40 N.m (30 lb ft).
9. Remove the transmission jack stand.
10. Connect the transfer case vent hose.
11. Install the clips to the transfer case brackets.
12. Connect the encoder motor electrical connector.
13. Install the inline connector to the harness bracket.
14. Connect the inline to engine harness electrical connector.
15. Connect the speed sensor electrical connector.
16. Install the transmission vent hose clip to the bracket, if equipped.
17. Install the transmission shift control cable clip to the transfer case.
18. Install the rear propeller shaft. Refer to «Propeller Shaft Replacement - One Piece»(ref-197434-S01803903062005101100000) or «Propeller Shaft Replacement - Two Piece»(ref-197434-S21627766012005101100000) in Propeller Shaft.
19. Install the front propeller shaft. Refer to «Propeller Shaft Replacement - Front»(ref-197434-S11772894682005101100000) in Propeller Shaft.
20. Fill the transfer case with fluid.
21. Install the transfer case shield, if equipped. Refer to «Transfer Case Shield Replacement»(/chevrolet/cab-chassis-silverado-3500/2004-2007/remont/transfer-case/#transfer-case-nvg-263-np1) .

Tools Required

J 42738 Seal Installer

1. Remove the transfer case. Refer to «Transfer Case Adapter Replacement»(/chevrolet/cab-chassis-silverado-3500/2004-2007/remont/transfer-case/#transfer-case-nvg-263-np1) .
2. Using a flat-tipped screwdriver, remove the input shaft seal.

1. Align the input seal evenly on the input shaft.
2. Using the J 42738 , install the input shaft seal.
3. Install the transfer case. Refer to «Transfer Case Adapter Replacement»(/chevrolet/cab-chassis-silverado-3500/2004-2007/remont/transfer-case/#transfer-case-nvg-263-np1) .
4. Check the fluid level, add fluid if necessary.

1. Remove the transfer case. Refer to «Transfer Case Assembly Replacement»(/chevrolet/cab-chassis-silverado-3500/2004-2007/remont/transfer-case/#transfer-case-nvg-263-np1) .
2. Remove the transfer case adapter bolts.
3. Remove the transfer case adapter.
4. Remove the transfer case adapter seal.
5. Remove the transfer case gasket, if necessary.

1. Install a NEW transfer case adapter seal.
2. Install the transfer case adapter. NOTE: Refer to «Fastener Notice»(ref-197335-S17275608472005101100000) in Cautions and Notices.
3. Install the transfer case adapter bolts. Tighten: Tighten the bolts to 50 N.m (37 lb ft).
4. Install the transfer case. Refer to «Transfer Case Assembly Replacement»(/chevrolet/cab-chassis-silverado-3500/2004-2007/remont/transfer-case/#transfer-case-nvg-263-np1) .

Scheme 35

The NVG 263 transfer case features a three button shift control switch located on the instrument panel. When the ignition is in the RUN position, the transfer case shift control module (TCCM) starts monitoring the transfer case shift control switch to determine if the driver desires a new mode/gear position. At a single press of the transfer case shift control switch, the lamp of the new desired position begins flashing to inform the driver that the TCCM has received the request for a new mode/gear position. The lamp continues to flash until all shifting criteria has been met and the new mode/gear position has been engaged. Once the new mode/gear position is fully active, the switch indicator for the new position remains ON constantly. In the event that the TCCM can not or will not complete the shift, the indicator returns to the previously selected position; this is a Transfer Case Shift Control Switch Indicator Flashes, then Returns to Previous Mode condition.

The NVG 263 transfer case provides the driver with 4 manual mode/gear positions

1. 2HI - 2 Wheel Drive high range
2. 4HI - 4 Wheel Drive high range
3. 4LO - 4 Wheel Drive low range
4. Neutral

The driver may choose to select any of these mode/gear positions while driving the vehicle. However, the transfer case will not allow a shift into or out of 4LO unless the following criteria has been met

1. The ignition switch is in RUN.
2. The automatic transmission is in Park or Neutral - clutch depressed on manual transmissions.
3. The vehicle speed is below 5 km/h (3 mph).

This transfer case also has a Neutral position. A shift to the Neutral position allows the vehicle to be towed without the rear axle rotating the transmission output shaft. Neutral position may be obtained only if the following criteria has been met

1. The ignition switch is in RUN.
2. The automatic transmission is in Park or Neutral - clutch depressed on manual transmissions.
3. The vehicle speed is below 5 km/h (3 mph).
4. The transfer case is in 2HI mode.

Once these conditions have been met, press and hold both the 2HI and 4LO buttons for 10 seconds. When the system completes the shift to neutral, the red neutral lamp illuminates.

A shift to the neutral position allows the vehicle to be towed without rotating the transmission output shaft. In the neutral position, the rear propeller shaft rotates the transfer case rear output shaft, in turn rotating the oil pump, thus providing constant lubrication during towing. This neutral position is a 4WD neutral, meaning the front and rear outputs of the transfer case are engaged as though in 4HI. With a disengaged front axle, there is no power flow to the front wheels, thus allowing towing with the front wheels off the ground or flat towing without driveline binding.

The NVG 263 transfer case is available in 2 variations, depending on the engine and transmission configurations. The variations allow the transfer case to handle different torque loads. When servicing the transfer case, it is important to understand which variation is being serviced because of the difference in parts.

NVG 263 Variations

The HD and the SHD model share many of the same components, but the increased torque capacity of the SHD requires a double row input bearing, larger diameter rear output shaft, rear output shaft bearing higher capacity, larger rear seal and case halves machined differently.

Some of the changes to the transfer case, that will take place during this model year, include the following

1. The oil pump suction pipe and screen will change to a 1 piece design.
2. The 2/4 wheel drive synchronizer gear and drive sprocket sleeve will change to a 1 piece design.

Scheme 36

The transfer case is shifted by an encoder motor (9) on the shift detent lever shaft. The shift detent lever shaft rotates the cam shaped shift detent lever (10) and moves the high/low range shift fork (11) or the 2/4 wheel drive mode shift fork (8). Depending on the selected mode or range, the shift forks move either the high/low range sleeve (4) for the high/low range planetary assembly (3) or the synchronizer sleeve (6) for the 2/4 wheel drive mode. In 2WD mode, the engine power from the transmission (1) is delivered to the input shaft (2). The engagement teeth on the inside of the input shaft (2) are engaged to the outer teeth on the high/low range sleeve (4). The high/low range sleeve (4) is slip splined to rear output shaft (5). The engine power flows from the high/low range sleeve (4) to the rear output shaft (5) and delivered to rear propeller shaft (7).

Scheme 37

In 4HI mode, the engine power from the transmission (1) is delivered to the input shaft (2). The engagement teeth on the inside of the input shaft (2) are engaged to the outer teeth on the high/low range sleeve (3). The high/low range sleeve (3) is slip splined to the rear output shaft (4). During a shift mode from 2HI to 4HI, the cam profile on the shift detent lever (14) pushes the 2/4 wheel drive mode shift fork (9) and the synchronizer sleeve. The sleeve, engaging the synchronizer (5), equalizes the front propeller shaft (12) and rear propeller shaft (7) speeds. The sleeve then engages to the 2/4 wheel drive synchronizer gear (8), which is splined to the drive sprocket (6). The engine power flow for driving the front propeller shaft (12), now travels from the rear output shaft (4) to the synchronizer hub, which is splined to the rear output shaft (4). The power flows from the synchronizer hub to the sleeve and then to 2/4 wheel drive synchronizer gear (8). The power flow is transmitted by a chain (10) to the driven sprocket on the front output shaft (11) and to the front propeller shaft (12). The front and rear propeller shafts are being driven at equal RPM, therefore giving a four wheel drive mode. This mode should only be used for extra traction. Using this mode on dry pavement causes tire scuffing when turning.

Scheme 38

During a range shift request to 4LO, a separate cam profile, on the same shift detent lever (12), moves the high/low shift fork (13). The high/low shift fork (13) moves the high/low range sleeve (6) rearward. The high/low range sleeve (6) outer teeth disengage from the input shaft (2) high-speed teeth. The high/low range sleeve (6) outer teeth then engage in the high/low planetary carrier teeth (5). The power flow is now from the transmission (1) to the planetary teeth on the input shaft (2) to the planetary gears (3) in the carrier. Rotating the planetary gears (3), which are engaged in the annulus gear (4), rotates the planetary carrier. The planetary carrier delivers the power to the high/low range sleeve (6). The high/low range sleeve (6) then drives the rear output shaft (7), providing a 2.72:1 gear ratio reduction to the rear output shaft (7). The 2/4 wheel drive synchronizer (8) is still engaged to drive the drive sprocket (9), as in the 4HI position, providing the engine power to the rear propeller shaft (10) and to the front propeller shaft (11).

Neutral Mode Power Flow

Shifting to the neutral position, the high/low range sleeve is centered between the input shaft and the high/low planetary carrier. The high/low range sleeve is not engaged with either the input shaft or the high/low planetary carrier teeth. The 2/4 wheel drive synchronizer is in the 4HI mode position.

Electrical Components

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.

Scheme 39

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 a linear encoder. 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.

Scheme 40

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 Control Module References in Computer/Integrating Systems.

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.

Special Tools

Special Tools Illustration Tool Number/Description J 8092 Driver Handle J 37668-A Seal Installer J 42738 Seal Installer J 43484 Output Shaft Seal Installer J 45380 Transfer Case Rear Bushing Remover and Installer

Scheme 41

Scheme 42

Scheme 43

Scheme 44

See also:
• Transfer Case Fluid Replacement
• DTC B0790
• Transfer Case Control Connector End Views
• Transfer Case Will Not Shift
• Transfer Case Popping Noise
• Transfer Case Whine or Rumble Noise
• Transfer Case Growl or Grinding Noise
• Transfer Case Clunk in 2HI Only
• Transfer Case Clunk in 4HI
• Transfer Case Clunk in 4LO
• Transfer Case Shudder or Binding
• Transfer Case Jumps Out of Gear
• Transfer Case Leak Diagnosis
• Symptoms - Transfer Case
• Transfer Case Output Shaft Seal Replacement - Rear