Transfer Case - Nvg 236/246-np8 Chevrolet Avalanche I

Fastener Tightening Specifications

Fastener Tightening Specifications

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Diagnostic Starting Point - Transfer Case

Begin the system diagnosis with the DIAGNOSTIC SYSTEM CHECK - Transfer Case . The Diagnostic System Check will provide the following information

1. The identification of the control modules that command the system
2. The ability of the control modules to communicate through the serial data circuit
3. The identification of any stored DTCs and their status

The use of the Diagnostic System Check will identify the correct procedure for diagnosing the system and where the procedure is located.

Diagnostic System Check - Transfer Case

These diagnostic procedures help you find and repair automatic transfer case (ATC) system malfunctions. This service category also contains information for repairing ATC system malfunctions. For best results, use the diagnostic tables and follow the sequence listed below

1. Perform the Transfer Case Diagnostic System Check. All ATC diagnostics must begin with the Transfer Case Diagnostic System Check. The Transfer Case Diagnostic System Check determines the following: Proper SERVICE 4WD indicator operation. Ability of the transfer case shift control module to communicate through the Data Link Connector (DLC) Existence of ATC DTCs
2. Refer to the diagnostic table as directed by the Transfer Case Diagnostic System Check. The diagnostic tables help enable you to diagnose any ATC system malfunction. Bypassing these procedures may result in the following: Extended diagnostic time Incorrect diagnosis Incorrect parts replacement
3. Repeat the Transfer Case Diagnostic System Check after you perform any repair or diagnostic procedure. This verifies that you correctly performed the repair. This also ensures that other malfunctions do not exist.

Test Description

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

1. This step inspects for lack of communication that may be due to a partial malfunction of the Class 2 serial data circuit or due to a total malfunction of the Class 2 serial data circuit. The specified procedure determines the particular condition.
2. The presence of DTCs indicates that the transfer case shift control module has detected a fault. Go to symptoms for other concerns.
3. The presence of DTCs which begin with "U" indicate some other module is not communicating. The specified procedure compiles all the available information before tests are performed.
4. Vehicle speed is provided to the transfer case shift control module via Class 2 and can effect the setting of DTC C0300. Perform the diagnostics for powertrain DTC P0502 and DTC P0503 first.
5. Perform diagnostics for DTC C0300 and DTC C0305 first before addressing other DTCs. DTC C0300 and DTC C0305 can be responsible for setting other DTCs.

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Scan Tool Data Definitions

ATC Application: The scan tool displays a numeric value. This parameter indicates the model number assigned to the transfer case.

ATC Software ID: The scan tool displays a numeric value. This parameter indicates the numbers or characters assigned to the current version of software used in the ATC module.

Auto 4WD Indicator: The scan tool displays ON or OFF. This parameter indicates if the Auto 4WD indicator light is being commanded by the transfer case shift control module.

Battery Voltage: The scan tool displays a range of 0-25.5 volts. This parameter indicates the voltage measured by the transfer case shift control module at the battery feed.

Current Slip Adapts: The scan tool displays a numeric value. This parameter indicates corrective adjustments made by the transfer case shift control module for wheel slip events.

Encoder Gear Position: The scan tool displays the different modes, Auto 4WD, 2WD High, 4WD High, 4WD Low, and Neutral. This parameter indicates the current mode in which the ATC is operating.

Encoder Return Voltage: The scan tool displays a range of 0-5 volts. This parameter indicates the voltage measured by the transfer case shift control module at the encoder signal return.

Encoder Supply Voltage: The scan tool displays a range of 0-7.5 volts. This parameter indicates the voltage measured by the transfer case shift control module at the encoder power.

Front Axle Requested: The scan tool displays YES or NO. This parameter indicates if the front axle switch has been requested by the transfer case shift control module.

Front Axle Switch: The scan tool displays Locked or Unlocked. This parameter indicates the feedback states of the front propshaft.

Front Propshaft Speed: The scan tool displays a range of 0-8, 192 RPM. This parameter indicates the rotational speed of the front propshaft.

Ignition Cycles Since Last Current DTC: The scan tool displays a numeric value. This parameter indicates how many ignition cycles have occurred since last current DTC was set.

Mode Switch Return Voltage: The scan tool displays a range of 0-5 volts. This parameter indicates the return voltage from the mode switch.

Mode Switch Selected: The scan tool displays ON or OFF. This parameter indicates the ATC mode switch button currently depressed by the driver.

Motor A Current: The scan tool displays Amps. This parameter indicates current flow when the motor moves one of two directions.

Motor B Current: The scan tool displays Amps. This parameter indicates current flow when the motor moves one of two directions.

Neutral Indicator: The scan tool displays ON or OFF. This parameter indicates if the Neutral Indicator Light is being commanded by the transfer case shift control module.

Rear Propshaft Speed: The scan tool displays a range of 0-8,192 RPM. This parameter indicates the rotational speed of the rear propshaft.

Service 4WD Lamp: The scan tool displays ON or OFF. This parameter indicates if the Service 4WD lamp is being commanded by the transfer case shift control module.

Slip Adapt PWM: The scan tool displays a range of 0-100 percent. This parameter indicates the Duty Cycle applied to the ATC motor.

Total Slippage: The scan tool displays a range of -32,767 to +32,767 RPM. This parameter indicates the total slippage of both the front and rear propshafts.

Transfer Case Lock: The scan tool displays Enabled or Disabled. This parameter indicates if the transfer case shift control module is commanding the transfer case motor brake ON.

2WD High Indicator: The scan tool displays ON or OFF. This parameter indicates if the 2WD high indicator light is being commanded by the transfer case shift control module.

4WD High Indicator: The scan tool displays ON or OFF. This parameter indicates if the 4WD high indicator light is being commanded by the transfer case shift control module.

4WD Low Active: The scan tool displays YES or NO. This parameter indicates whether or not the 4WD Active mode is active.

4WD Low Indicator Light: The scan tool displays ON or OFF. This parameter indicates if the 4WD low indicator light is being commanded by the transfer case shift control module.

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

Conditions for Running the DTC

1. The ignition is ON.
2. 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.

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

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

The range/mode switch circuit consists of 5 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, AWD, 2HI, 4HI, or 4LO mode was selected by the driver.

1. The ignition is ON.
2. 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.

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

The rear propshaft speed sensor is a permanent magnet (PM) generator. The PM generator produces a pulsing AC voltage. The AC voltage level and number of pulses increases as speed increases. The module converts the pulsating AC voltage to a propshaft RPM which is used for calculations. The propshaft RPM can be displayed with a scan tool.

This DTC detects an open, short to ground, short to voltage or faulty sensor.

1. The ignition is ON.
2. System voltage is 9-18 volts.
3. Vehicle speed exceeds 16 km/h (10 mph).

The system logs the DTC if the rear propshaft input indicates a speed of less than 16 RPM for 30 seconds while all of the following are true

1. Transmission NOT in Park/Neutral
2. Engine is running
3. Front axle is engaged
4. Vehicle speed on Class 2 data bus exceeds 16 km/h (10 mph)

1. All shifts to AUTO, or the Adapt mode is disabled. If the current mode is AUTO, the system does not allow any further adaptive events, such as correcting slip.
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.

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1. This step tests to see if the malfunction is intermittent.
2. This step tests the internal resistance of the propshaft speed sensor.
3. This step tests to see if the propshaft speed sensor can generate a sufficient amount of AC voltage.
4. This step tests the rear speed sensor low circuit for a short to ground, a high resistance, or an open.
5. This step tests the rear speed sensor high circuit for a short to ground, a high resistance or an open.
6. This step tests the rear speed sensor low circuit for a short to voltage.
7. This step tests the rear speed sensor high circuit for a short to voltage.
8. This step tests the rear speed sensor low circuit for a short to the rear speed sensor high circuit.

The front propshaft speed sensor is a permanent magnet (PM) generator. The PM generator produces a pulsing AC voltage. The AC voltage level and number of pulses increases as speed increases. The transfer case shift control module converts the pulsating AC voltage to a propshaft RPM which is used for the following functions

1. Calculations
2. To monitor the difference between the front and rear propshaft speed
3. In the AUTO, or the Adapt mode of operation, to determine the amount of slip and the percent of torque to apply to the front axle

The module accesses this input when the vehicle is in AUTO mode, 4HI, and 4LO ranges. The propshaft RPM can be displayed with a scan tool.

This DTC detects an open, short to ground, short to voltage or faulty sensor.

1. The ignition is ON.
2. System voltage is 9-18 volts.
3. Vehicle speed exceeds 16 km/h (10 mph).

The system logs the DTC if the front propshaft input indicates a speed of less than 16 RPM for 30 seconds while all of the following are true

1. Transmission NOT in Park/Neutral
2. Engine is running
3. Front axle is engaged
4. Rear propshaft speed exceeds 512 RPM
5. Vehicle speed on Class 2 Data bus exceeds 16 km/h (10 mph)

1. All shifts to AUTO mode are disabled. If the current mode is AUTO, the system does not allow any further adaptive events, such as correcting the slip.
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.

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1. This step tests to see if the malfunction is intermittent.
2. This step tests the internal resistance of the propshaft speed sensor.
3. This step tests to see if the propshaft speed sensor can generate a sufficient amount of AC voltage.
4. This step tests the forward speed sensor low signal circuit for a short to ground, a high resistance or an open.
5. This step tests the forward speed sensor high signal circuit for a short to ground, a high resistance or an open.
6. This step tests the forward speed sensor low signal circuit for a short to voltage.
7. This step tests the forward speed sensor high signal circuit for a short to voltage.
8. This step tests the forward speed sensor low signal circuit for a short to the forward speed sensor high circuit.

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. 4HI
2. The AUTO or the Adapt mode
3. 2HI
4. N
5. 4LO

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.

1. The ignition is ON.
2. 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.

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

The transfer case shift control module controls the transfer case lock solenoid.

The transfer case lock solenoid is released by being energized. This is accomplished by grounding the lock solenoid control circuit during gears shifts, and in the AUTO or adapt mode. Locking action is applied when power or ground are taken away from the lock solenoid, the transfer case motor is prevented from moving. The system is capable of providing a 2HI, 4HI and 4LO lock-up without the need of additional vehicle power to hold the transfer case in these positions.

This DTC detects an open lock solenoid coil, open motor lock control circuit, or an open motor lock feed circuit.

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

1. The transfer case shift control module tries to unapply, turn OFF the lock solenoid by grounding the motor control circuit.
2. If the module does not sense the battery voltage at the motor lock control circuit prior to applying the motor lock, the DTC sets.
3. Transfer Case Lock output reads back as a high voltage when a low voltage is expected.

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 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.

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1. Listen for an audible click when the encoder motor brake operates. Command both the ON and OFF states. Repeat the commands as necessary.
2. This step tests for voltage at the lock solenoid feed side of the encoder motor lock solenoid.
3. This step verifies that the lock solenoid battery positive circuit is not shorted to power, shorted to ground, or have high resistance.
4. This step determines if the encoder motor lock solenoid is faulty by checking the internal resistance.
5. This step tests the control circuit of the encoder motor brake for a short to voltage or an open.
6. This step determines if a corroded or damaged connector in the encoder motor harness is the cause

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. A 5 volt reference circuit
2. An encoder signal circuit
3. An encoder low reference circuit

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

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.

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1. This step checks for a voltage reading on the scan tool.
2. This step tests the encoder circuit for a current malfunction.
3. This step tests for an internal encoder malfunction which is present only in certain areas of the encoder sensor.
4. This step tests for proper reference voltage at the encoder.
5. This step tests the 5 volt regulator encoder circuit for a short to voltage, short to ground, an open or high resistance.
6. 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.
7. This step tests the encoder signal circuit and the encoder low reference circuit for a short to voltage.
8. This step helps determine a faulty encoder.
9. This step tests the encoder signal circuit and the encoder low reference circuit for an open or a short to ground.

The 4WD LO circuit is used to notify the powertrain control module (PCM) that the vehicle is in 4WD low range. The PCM 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 LO circuit.

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

1. After the transfer case shift control module grounds the output, the 4WD LO 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 LO 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.

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

The transfer case shift control module senses rear slip. After several attempts of applying torque to the front wheels, by activating the encoder motor, the transfer case still sees a difference in speed between the front propshaft speed sensor and rear propshaft speed sensor.

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

The transfer case shift control module is unable to correct sensed wheel slip for 10 consecutive seconds.

1. All shifts to Auto Mode are disabled. If the current mode is Auto, the system will not allow any further adaptive events, such as correcting slip.
2. The SERVICE 4WD indicator remains illuminated for the remainder of the current ignition cycle.

1. A history DTC will clear after 100 consecutive ignition cycles without a fault present.
2. Use a scan tool in order to clear history and current DTCs.

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

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1. This step determines if the rear propshaft speed sensor and wiring are operating properly.
2. This step determines if the front propshaft speed sensor and wiring are operating properly.
3. This step determines if the motor control A or motor control B circuits are shorted to ground within the encoder motor.
4. This step tests the integrity of the motor windings.
5. This step tests the motor control A and motor control B circuits for an open, short to ground, or high resistance between the encoder motor and the transfer case shift control module.
6. This step determines whether the transfer case is mechanically functioning properly.

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 (PM) 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 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.

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

1. The ignition is ON.
2. 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.

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

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

1. The ignition is ON.
2. 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 - Transfer Case.

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

Scheme 57

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

Symptoms - Transfer Case

Important

1. Perform the Diagnostic System Check - Transfer Case before using the symptom tables in order to verify that the following statements are true: DTCs are not set. The control modules can communicate via the serial data link.
2. Review the system operation in order to familiarize yourself with the system functions. Refer to «TRANSFER CASE DESCRIPTION AND OPERATION»(/chevrolet/avalanche/i-2001-2006/remont/transfer-case/#transfer-case-nvg-236246-np8) .

Visual/Physical Inspection

1. Inspect for aftermarket devices which could affect the operation of the automatic transfer case system. Refer to CHECKING AFTERMARKET ACCESSORIES in Wiring Systems.
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 AND POOR CONNECTIONS in Wiring Systems.

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/avalanche/i-2001-2006/remont/transfer-case/#transfer-case-nvg-236246-np8)
2. «FRONT AXLE WILL NOT DISENGAGE»(/chevrolet/avalanche/i-2001-2006/remont/transfer-case/#transfer-case-nvg-236246-np8)
3. «TRANSFER CASE SHIFT CONTROL SWITCH INOPERATIVE»(/chevrolet/avalanche/i-2001-2006/remont/transfer-case/#transfer-case-nvg-236246-np8)
4. «NO CORRECTION FOR SLIP IN AWD MODE»(/chevrolet/avalanche/i-2001-2006/remont/transfer-case/#transfer-case-nvg-236246-np8)
5. «SERVICE INDICATOR ALWAYS ON»(/chevrolet/avalanche/i-2001-2006/remont/transfer-case/#transfer-case-nvg-236246-np8)
6. «SERVICE INDICATOR INOPERATIVE»(/chevrolet/avalanche/i-2001-2006/remont/transfer-case/#transfer-case-nvg-236246-np8)
7. «TRANSFER CASE SHIFT CONTROL SWITCH INDICATOR ALWAYS ON - TWO OR MORE»(/chevrolet/avalanche/i-2001-2006/remont/transfer-case/#transfer-case-nvg-236246-np8)
8. «TRANSFER CASE SHIFT CONTROL SWITCH INDICATOR FLASHES, THEN RETURNS TO PREVIOUS MODE»(/chevrolet/avalanche/i-2001-2006/remont/transfer-case/#transfer-case-nvg-236246-np8)
9. «TRANSFER CASE SHIFT CONTROL SWITCH INDICATORS FLASH CONTINUOUSLY 15 SECONDS OR MORE»(/chevrolet/avalanche/i-2001-2006/remont/transfer-case/#transfer-case-nvg-236246-np8)
10. «TRANSFER CASE SHIFT CONTROL SWITCH INDICATOR INOPERATIVE - ONE OR MORE»(/chevrolet/avalanche/i-2001-2006/remont/transfer-case/#transfer-case-nvg-236246-np8)
11. «Transfer Case Popping Noise»(/chevrolet/avalanche/i-2001-2006/remont/transfer-case/#transfer-case-nvg-236246-np8)
12. «Transfer Case Whine or Rumble Noise»(/chevrolet/avalanche/i-2001-2006/remont/transfer-case/#transfer-case-nvg-236246-np8)
13. «Transfer Case Growl or Grinding Noise»(/chevrolet/avalanche/i-2001-2006/remont/transfer-case/#transfer-case-nvg-236246-np8)
14. «Transfer Case Grating Noise»(/chevrolet/avalanche/i-2001-2006/remont/transfer-case/#transfer-case-nvg-236246-np8)
15. «Transfer Case Clunk in 2HI Only»(/chevrolet/avalanche/i-2001-2006/remont/transfer-case/#transfer-case-nvg-236246-np8)
16. «Transfer Case Clunk in 4HI»(/chevrolet/avalanche/i-2001-2006/remont/transfer-case/#transfer-case-nvg-236246-np8)
17. «Transfer Case Clunk in 4LO»(/chevrolet/avalanche/i-2001-2006/remont/transfer-case/#transfer-case-nvg-236246-np8)
18. «Transfer Case Clunk during Acceleration and Deceleration»(/chevrolet/avalanche/i-2001-2006/remont/transfer-case/#transfer-case-nvg-236246-np8)
19. «Transfer Case Shudder or Binding»(/chevrolet/avalanche/i-2001-2006/remont/transfer-case/#transfer-case-nvg-236246-np8)
20. «Transfer Case Will Not Shift»(/chevrolet/avalanche/i-2001-2006/remont/transfer-case/#transfer-case-nvg-236246-np8)
21. «Transfer Case Jumps Out of Gear»(/chevrolet/avalanche/i-2001-2006/remont/transfer-case/#transfer-case-nvg-236246-np8)

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 (PM) 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 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.

Scheme 58

Scheme 59

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

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 (PM) 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 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.

Scheme 60

Scheme 61

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

The range/mode switch circuit consists of the following 5 switches

1. 4HI
2. AUTO 4WD
3. 2HI
4. 4LO
5. 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. 4HI
2. AUTO 4WD
3. 2HI
4. 4LO

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

Scheme 62

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.

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

Scheme 63

1. 2. This step helps determine whether the front axle switch is functioning properly.
2. 3. This step helps determine whether the front axle switch is locking and unlocking.
3. 4. This step tests transfer case clutch performance.

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.

Scheme 64

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

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.

Scheme 65

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

The indicator lamps circuit consist of the following 5 individual lamps contained inside the mode/range switch assembly

1. 4HI
2. AUTO 4WD
3. 2HI
4. 4LO
5. Neutral

The following lamps are contained inside their respective range button

1. 4HI
2. AUTO 4WD
3. 2HI
4. 4LO
5. Neutral

When the ignition in ON, the transfer case shift control module illuminates the indicator that corresponds to the current automatic temperature control (ATC) 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.

Scheme 66

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 lamp circuits.
3. 4. This step tests the suspect lamp circuits for a short to ground.
4. 5. This step repairs a short to ground in the suspect lamp circuit.

The transfer case shift control module controls the transfer case lock solenoid. The transfer case lock solenoid is released by being energized. This is accomplished by grounding the lock solenoid control circuit during gear shifts, and in the AUTO or adapt mode. Locking action is applied when power or ground are taken away from the lock solenoid, the transfer case motor is prevented from moving. The system is capable of providing a 2HI, 4HI and 4LO lock-up without the need of additional vehicle power to hold the transfer case in these positions.

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: 4HI, the AUTO or the Adapt mode (AWD), 2HI, Neutral (N) and 4LO.

If there is a fault in the brake control circuit, 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 will also go into shift block mode if there is a mechanical concern causing the shift lever detent shaft to bind, or 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.

Scheme 67

Scheme 68

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.
8. 9. This step determines if a short to ground, short to voltage, open, or high resistance on the transfer case lock circuit is causing a shift block.
9. 10. This step replaced the encoder motor assembly.

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 a permanent magnetic (PM) 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 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.

Scheme 69

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.

The indicator lamps circuit consist of 5 individual lamps contained inside the mode/range switch assembly. The following lamps are contained inside the respective range button

1. AUTO 4WD
2. 2HI
3. 4HI
4. 4LO

Each time the ignition is cycled, all 5 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 ATC 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.

Scheme 70

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 lamp circuit for an open or high resistance.
4. 5. This step tests the lamp feed circuit for an open or short to ground.

Scheme 71

Scheme 72

Scheme 73

Scheme 74

Scheme 75

Scheme 76

Scheme 77

Scheme 78

Scheme 79

Scheme 80

Scheme 81

Scheme 82

Scheme 83

Scheme 84

Scheme 85

1. Raise and suitably support the vehicle. Refer to «LIFTING AND JACKING THE VEHICLE»(/chevrolet/avalanche/i-2001-2006/remont/hoistjack/#jacking-and-lifting-avalanche__lifting-and-jacking-the-vehicle) in General Information.
2. Remove the transfer case shield bolts, if equipped.
3. Remove the transfer case shield, if equipped.

Scheme 86

1. Position the transfer case shield, if equipped. NOTE: Refer to «FASTENER NOTICE»(/chevrolet/avalanche/i-2001-2006/remont/oem-general-information/#gm-vehicles-cautions-notices__fastener-notice) in Cautions and Notices.
2. Install the transfer case shield bolts, if equipped. Tighten Tighten the bolts to 20 N.m (15 lb ft).
3. Lower the vehicle.

Removal Procedure

Important: When performing the following procedures, use only hand tools to remove and install the drain and fill plugs.

Scheme 87

Scheme 88

1. Raise and suitably support the vehicle. Refer to «LIFTING AND JACKING THE VEHICLE»(/chevrolet/avalanche/i-2001-2006/remont/hoistjack/#jacking-and-lifting-avalanche__lifting-and-jacking-the-vehicle) in General Information.
2. Remove the transfer case shield, if equipped. Refer to «TRANSFER CASE SHIELD REPLACEMENT»(/chevrolet/avalanche/i-2001-2006/remont/transfer-case/#transfer-case-nvg-236246-np8) .
3. Remove the fill plug.
4. Remove the drain plug.

Installation Procedure

Note. Refer to FASTENER NOTICE in Cautions and Notices.

Important: Use only drain and fill plugs that are made from aluminum. Steel or brass plugs are not compatible with the magnesium case.

Scheme 89

Scheme 90

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 Auto-Trak II, transfer case fluid, GM P/N 12378508 (Canadian P/N 10953626).
3. Install the fill plug. Tighten Tighten the plug to 20 N.m (15 lb ft).
4. Install the transfer case shield, if equipped. Refer to «TRANSFER CASE SHIELD REPLACEMENT»(/chevrolet/avalanche/i-2001-2006/remont/transfer-case/#transfer-case-nvg-236246-np8) .
5. Lower the vehicle.

Scheme 91

Scheme 92

1. Remove the transfer case shield, if equipped. Refer to «TRANSFER CASE SHIELD REPLACEMENT»(/chevrolet/avalanche/i-2001-2006/remont/transfer-case/#transfer-case-nvg-236246-np8) .
2. Remove the front propeller shaft. Refer to PROPELLER SHAFT REPLACEMENT - FRONT in Propeller Shaft.
3. Disconnect the transfer case switch electrical connector (2).
4. Disconnect the encoder motor electrical connector (7).
5. Remove the encoder motor bolts.
6. Remove the encoder motor.
7. Remove the actuator insulator gasket.
8. If replacing the encoder motor, remove the locating pins from the old motor.

Important

1. If the encoder motor is being replaced, ensure that the transfer case is in the neutral position. Manually shift the transfer case at the shift shaft, using a crescent wrench if necessary.
2. When installing the encoder motor, ensure that the encoder motor is indexed correctly and the motor is flat against the transfer case before tightening the bolts.
3. A NEW encoder motor does NOT come with locating pins.

Scheme 93

Scheme 94

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»(/chevrolet/avalanche/i-2001-2006/remont/oem-general-information/#gm-vehicles-cautions-notices__fastener-notice) 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 (7).
6. Connect the transfer case switch electrical connector (2).
7. Install the front propeller shaft. Refer to PROPELLER SHAFT REPLACEMENT - FRONT in Propeller Shaft.
8. Install the transfer case shield, if equipped. Refer to «TRANSFER CASE SHIELD REPLACEMENT»(/chevrolet/avalanche/i-2001-2006/remont/transfer-case/#transfer-case-nvg-236246-np8) .

Scheme 95

Scheme 96

1. Remove the transfer case shield, if equipped. Refer to «TRANSFER CASE SHIELD REPLACEMENT»(/chevrolet/avalanche/i-2001-2006/remont/transfer-case/#transfer-case-nvg-236246-np8) .
2. Disconnect the front speed sensor electrical connector (5).
3. Remove the front speed sensor.

Note. Refer to FASTENER NOTICE in Cautions and Notices.

Scheme 97

Scheme 98

1. Install the front speed sensor. Tighten Tighten the speed sensor to 15 N.m (11 lb ft).
2. Connect the front speed sensor electrical connector (5).
3. Install the transfer case shield, if equipped. Refer to «TRANSFER CASE SHIELD REPLACEMENT»(/chevrolet/avalanche/i-2001-2006/remont/transfer-case/#transfer-case-nvg-236246-np8) .

Scheme 99

Scheme 100

1. Raise and suitably support the vehicle. Refer to «LIFTING AND JACKING THE VEHICLE»(/chevrolet/avalanche/i-2001-2006/remont/hoistjack/#jacking-and-lifting-avalanche__lifting-and-jacking-the-vehicle) in General Information.
2. Disconnect the left rear speed sensor electrical connector (4).
3. Remove the left rear speed sensor.

Note. Refer to FASTENER NOTICE in Cautions and Notices.

Scheme 101

Scheme 102

1. Install the left rear speed sensor. Tighten Tighten the speed sensor to 15 N.m (11 lb ft).
2. Connect the left rear speed sensor electrical connector (4).
3. Lower the vehicle.

Scheme 103

Scheme 104

1. Raise and suitably support the vehicle. Refer to «LIFTING AND JACKING THE VEHICLE»(/chevrolet/avalanche/i-2001-2006/remont/hoistjack/#jacking-and-lifting-avalanche__lifting-and-jacking-the-vehicle) in General Information.
2. Disconnect the right rear speed sensor electrical connector (3).
3. Remove the right rear speed sensor.

Note. Refer to FASTENER NOTICE in Cautions and Notices.

Scheme 105

Scheme 106

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

Transfer Case Output Shaft Seal Replacement - Front

Tools Required

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

Scheme 107

Scheme 108

Scheme 109

Scheme 110

Scheme 111

1. Remove the transfer case shield, if equipped. Refer to «TRANSFER CASE SHIELD REPLACEMENT»(/chevrolet/avalanche/i-2001-2006/remont/transfer-case/#transfer-case-nvg-236246-np8) .
2. Remove the front propeller shaft. Refer to PROPELLER SHAFT REPLACEMENT - FRONT 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 race from the seal.
7. Insert a flat-tipped screwdriver or a small pry bar in the space between the outer race of the seal and transfer case.
8. Remove the outer part of the seal.

Scheme 112

1. Install the J 43484 (2) to the J 8092 (1).
2. Install the seal onto the J 43484 .
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 in Propeller Shaft.
5. Check the fluid level. Add fluid if necessary.
6. Install the transfer case shield, if equipped. Refer to «TRANSFER CASE SHIELD REPLACEMENT»(/chevrolet/avalanche/i-2001-2006/remont/transfer-case/#transfer-case-nvg-236246-np8) .

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

Scheme 113

Scheme 114

1. Remove the transfer case shield, if equipped. Refer to «TRANSFER CASE SHIELD REPLACEMENT»(/chevrolet/avalanche/i-2001-2006/remont/transfer-case/#transfer-case-nvg-236246-np8) .
2. Remove the rear propeller shaft. Refer to PROPELLER SHAFT REPLACEMENT - REAR 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.

Scheme 115

Scheme 116

1. Using the J 45380 , install a NEW output shaft bushing. 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. Important: Ensure the drain hole on the boot of the rear output shaft seal is facing down toward the ground.
2. Using the J 37668-A , install a NEW front output shaft seal.
3. Install the rear propeller shaft. Refer to PROPELLER SHAFT REPLACEMENT - REAR in Propeller Shaft.
4. Check the fluid level. Add fluid if necessary.
5. Install the transfer case shield, if equipped. Refer to «TRANSFER CASE SHIELD REPLACEMENT»(/chevrolet/avalanche/i-2001-2006/remont/transfer-case/#transfer-case-nvg-236246-np8) .

Scheme 117

Scheme 118

Scheme 119

1. Remove the transfer case shield, if equipped. Refer to «TRANSFER CASE SHIELD REPLACEMENT»(/chevrolet/avalanche/i-2001-2006/remont/transfer-case/#transfer-case-nvg-236246-np8) .
2. Remove the front propeller shaft. Refer to PROPELLER SHAFT REPLACEMENT - FRONT in Propeller Shaft.
3. Remove the rear propeller shaft. Refer to PROPELLER SHAFT REPLACEMENT - REAR in Propeller Shaft.
4. Remove the vent hose (2) from the transfer case fitting (1).
5. Reposition the vent hose out of the way.
6. Remove the harness inline to engine harness connector (1) clip from the fuel feed and return pipe bracket.
7. Disconnect the encoder motor electrical connector (7).
8. Disconnect the speed sensor electrical connectors (3, 4, and 5).
9. Remove the harness clips (6, 8) from the transfer case.
10. Reposition the harness out of the way. Important: Ensure that the transfer case is correctly secured to the transmission jack.
11. Support the transfer case with a suitable transmission jack. Important: When removing the transfer case from the transmission, do not remove the transmission mount or the transfer case adapter.
12. Remove the transfer case adapter nuts.
13. Remove the fuel feed and return pipe bracket.
14. Separate the transfer case from the transmission by moving the transfer case straight back toward the rear of the vehicle.
15. Rotate the transfer case so that the transfer case is perpendicular to the transmission.
16. Lower the transfer case.

Scheme 120

Scheme 121

Scheme 122

1. Rotate the transfer case so that the transfer case is perpendicular to the transmission.
2. Raise the transfer case into position.
3. Rotate the transfer case so that the transfer case aligns with the transfer case adapter.
4. Install the transfer case.
5. Install the fuel feed and return pipe bracket. NOTE: Refer to «FASTENER NOTICE»(/chevrolet/avalanche/i-2001-2006/remont/oem-general-information/#gm-vehicles-cautions-notices__fastener-notice) in Cautions and Notices.
6. Install the transfer case adapter nuts. Tighten Tighten the nuts to 50 N.m (37 lb ft).
7. Remove the transmission jack from the transfer case.
8. Position the harness to the transfer case.
9. Install the harness clips (6, 8) to the transfer case.
10. Connect the speed sensor electrical connectors (3, 4, and 5).
11. Connect the encoder motor electrical connector (7).
12. Install the harness inline to engine harness connector (1) clip to the fuel feed and return pipe bracket.
13. Position the vent hose to the transfer case.
14. Install the vent hose (2) to the transfer case fitting (1).
15. Install the rear propeller shaft. Refer to PROPELLER SHAFT REPLACEMENT - REAR in Propeller Shaft.
16. Install the front propeller shaft. Refer to PROPELLER SHAFT REPLACEMENT - FRONT in Propeller Shaft.
17. Install the transfer case shield, if equipped. Refer to «TRANSFER CASE SHIELD REPLACEMENT»(/chevrolet/avalanche/i-2001-2006/remont/transfer-case/#transfer-case-nvg-236246-np8) .

Transfer Case Input Shaft Seal Replacement

Tools Required

J 42738 Seal Installer

Scheme 123

1. Remove the transfer case. Refer to «TRANSFER CASE ASSEMBLY REPLACEMENT»(/chevrolet/avalanche/i-2001-2006/remont/transfer-case/#transfer-case-nvg-236246-np8) .
2. Using a flat-tipped screwdriver, remove the input shaft seal.

Important: When installing the input shaft seal, make sure that the part numbers on the seal are facing outward (away from the body of the transfer case).

Scheme 124

1. Align the transfer case input shaft seal evenly on the input shaft. Important: The input shaft seal should be even with the surface of the transfer case after installation.
2. Using the J 42738 , install the transfer case input shaft seal.
3. Install the transfer case. Refer to «TRANSFER CASE ASSEMBLY REPLACEMENT»(/chevrolet/avalanche/i-2001-2006/remont/transfer-case/#transfer-case-nvg-236246-np8) .
4. Check the fluid level. Add fluid if necessary.

Scheme 125

Scheme 126

Scheme 127

Scheme 128

Scheme 129

Scheme 130

1. Remove the transfer case. Refer to «TRANSFER CASE ASSEMBLY REPLACEMENT»(/chevrolet/avalanche/i-2001-2006/remont/transfer-case/#transfer-case-nvg-236246-np8) .
2. Support the transmission with a suitable jack stand.
3. Remove the transmission mount nuts.
4. Remove the crossmember bolts.
5. Remove the crossmember.
6. Remove the transmission mount bolts.
7. Remove the transmission mount.
8. Remove the transfer case adapter bolts.
9. Remove the transfer case adapter.
10. Remove the transfer case seal.
11. Remove the transfer case gasket, if necessary.

Important: If the gasket or the seal becomes damaged, replace it. DO NOT use any type of silicone sealer or liquid gasket maker in place of the seal or gasket.

Scheme 131

Scheme 132

Scheme 133

Scheme 134

Scheme 135

Scheme 136

1. Install a NEW transfer case adapter seal.
2. Install the transfer case adapter. NOTE: Refer to «FASTENER NOTICE»(/chevrolet/avalanche/i-2001-2006/remont/oem-general-information/#gm-vehicles-cautions-notices__fastener-notice) 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 transmission mount.
5. Install the transmission mount bolts. Tighten Tighten the bolts to 47 N.m (35 Lb ft).
6. Install the crossmember.
7. Install the crossmember bolts. Tighten Tighten the bolts to 70 N.m (52 Lb ft).
8. Install the transmission mount nuts. Tighten Tighten the nuts to 40 N.m (30 Lb ft).
9. Remove the transmission jack.
10. Install a NEW transfer case gasket, if necessary.
11. Install the transfer case. Refer to «TRANSFER CASE ASSEMBLY REPLACEMENT»(/chevrolet/avalanche/i-2001-2006/remont/transfer-case/#transfer-case-nvg-236246-np8) .
12. Check the fluid level. Add fluid if necessary.

Scheme 137

Scheme 138

1. Remove the instrument panel (I/P) cluster bezel. Refer to BEZEL REPLACEMENT - INSTRUMENT PANEL (I/P) CLUSTER in Instrument Panel, Gages, and Console.
2. Using a flat-tipped screwdriver, gently pry the retaining clips open on the housing.
3. Slide out the selector switch until the electrical connectors are accessible.
4. Disconnect the selector switch electrical connectors (2, 3).
5. Remove the selector switch from the housing.

Scheme 139

Scheme 140

1. Position the selector switch close to the housing so the electrical connectors can be connected.
2. Connect the selector switch electrical connectors (2, 3).
3. Slide the selector switch into the housing until the switch snaps into place. Important: Make sure that the selector switch is seated properly in the housing before installing the IP cluster bezel.
4. Install the I/P cluster bezel. Refer to BEZEL REPLACEMENT - INSTRUMENT PANEL (I/P) CLUSTER in Instrument Panel, Gages, and Console.

Scheme 141

Scheme 142

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

Scheme 143

Scheme 144

1. Install the shift control module to the bracket.
2. Connect the shift control module electrical connectors.
3. Start the engine and test the automatic transfer case system for proper shift operation.

Set-up for Module Programming/Reprogramming

Important: Ensure that the vehicle battery is fully charged and that a battery charger is no longer connected. If performing this procedure for module replacement, install new module before proceeding. Before reprogramming close the doors and wait two minutes to allow other modules to stop communicating via the class 2 data line. Failure to do so could result in a failed reprogramming procedure.

1. Turn OFF all accessories.
2. Turn ON the ignition, with the engine OFF.

Remote Programming Feature

1. Connect the scan tool to the vehicle.
2. Power-up the scan tool and select the Service Programming feature.
3. Select the appropriate vehicle.
4. Press the Request Info button on the scan tool.
5. Connect the scan tool to the computer station.
6. Follow the menu select items for reprogramming and provide information as to what type of device you are programming and whether you are reprogramming or replacing the electronic control unit (ECU).
7. Select "vehicle" from the selection menu.
8. Select the module you wish to Program.
9. Select "Normal" for Programming Type.
10. Select the applicable software calibrations.
11. Transfer data file to the scan tool.
12. Reconnect the scan tool to the vehicle.
13. Turn ON the ignition, with the engine OFF.
14. Select the Service Programming feature on the scan tool.
15. Press the Program button on the scan tool.

Programming Using Scan Tool Pass-Through Connection

1. Connect the scan tool to vehicle and power it up.
2. Connect the computer station to the scan tool.
3. Select "PC Using Scan Tool Connection" from the programming menu on the computer station.
4. Follow the menu select items for reprogramming and provide information as to what type of device you are programming and whether you are reprogramming or replacing the electronic control unit (ECU).
5. Select "vehicle" from the selection menu.
6. Select the module you wish to program.
7. Select "Normal" for Programming Type.
8. Select the applicable software calibrations.
9. Transfer data file to the scan tool.

Scheme 145

The New Venture Gear model NVG 246 RPO NP8 transfer case is a two speed automatic, active, transfer case. The NVG 246 transfer case has many changes from prior years. The NVG 246 is now classified as an Electronic Architect Upgrade (EAU). The upgrades to the NVG 246 EAU include some of the following internal changes

1. A new encoder motor for faster operation in the AWD mode.
2. The control actuator lever (3) is a new design with different cam angles.
3. The shift detent plunger and spring is no longer used.
4. The clutch assembly (1) uses a new style return spring and clutch washer.
5. A new rear output shaft (2) no longer uses a retaining ring by the oil pump.
6. The range shift fork (4) is a newer design.

The NVG 246 EAU provides 5 modes, Auto 4WD, 4HI, 4LO, 2HI and Neutral. The Auto 4WD position allows the capability of an active transfer case, which provides the benefits of on-demand torque biasing wet clutch and easy vehicle tuning through software calibrations. The software calibrations allow more features such as flexible adapt ready position and clutch preload torque levels. The technology allows for vehicle speed dependent clutch torque levels to enhance the performance of the system. For example, the system is calibrated to provide 0-5 ft Lb of clutch torque during low speed, low engine torque operation, and predetermined higher torque for 40 km/h (25 mph) and greater. This prevents crow-hop and binding at low speeds and provides higher torque biases at higher vehicle speeds, in order to enhance stability.

The NVG 246 EAU transfer case features a 4 button shift control switch located on the instrument panel. When the ignition key is in the RUN position, the transfer case shift control module monitors the transfer case shift control switch to determine if the driver desires a new mode/range position. At a single press of the transfer case shift control switch, the lamp of the new desired position will begin flashing to inform the driver that the transfer case shift control module has received the request for a new mode/range position. The lamp will continue to flash until all shifting criteria has been met and the new mode/range position has been reached, or has been engaged. Once the new mode/range position is fully active, the switch indicator lamp for the new position will remain ON constantly.

During normal driving situations, the transfer case can operate in the Auto 4WD mode. In the Auto 4WD mode, the transfer case shift control module monitors rear wheel slip speed, based on the inputs from both the front and rear propshaft speed sensors. When the vehicle experiences a rear wheel slip condition, the transfer case shift control module sends a pulse width modulated (PWM) signal to an electronic motor, which is the transfer case encoder motor. This motor rotates the transfer case control actuator lever shaft, applying a clutch pack. This clutch pack is designed to deliver a variable amount of torque, normally delivered to the rear wheels, and transfers it to the front wheels. Torque is ramped up to the front wheels until the front propshaft speed sensor matches that of the rear propshaft speed sensor. Torque is ramped down to the front wheels. The process would repeat if rear wheel slip is detected again.

The NVG 246 EAU transfer case has the added feature of also providing the driver with 3 manual mode/range positions

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

The driver may choose to select any of these mode/range 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 engine is running.
2. The automatic transmission is in Neutral.
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 rotating the transmission output shaft. Neutral position may be obtained only if the following criteria has been met

1. The engine is running.
2. The automatic transmission is in Neutral.
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 will illuminate.

The NVG 246 EAU case halves are high-pressure die-cast magnesium. Ball bearings support the input shaft, the front output shaft, and the rear output shaft. A thrust bearing is located inside of the input shaft gear to support the front of the rear output shaft. The transfer case requires Auto Trac® II Fluid GM P/N 12378508 (Canadian P/N 10953626) which is blue in color. The fluid is designed for smooth clutch application. An oil pump, driven by the rear output shaft, pumps the fluid through the rear output shaft oil gallery to the clutch and bearings.

There are two versions of the NVG 246 EAU, which depend on the transmission applications and vehicle applications. If the vehicle is equipped with a transmission RPO M30, the transmission splines in the input gear will have 27 teeth. With this application the planetary carrier assembly will have 4 pinion gears. If the vehicle is equipped with transmission RPO MT1 or MN8, the transmission splines in the input gear will have 32 teeth. The planetary carrier assembly on this application will have 6 pinion gears.

Scheme 146

When the NVG 246 EAU is in the 2HI mode, the power flows from the transmission (1) to the input shaft gear (2). The input shaft gear (2) is connected to the rear output shaft (4) by the high/low range collar (3). The range collar (3) outer teeth are engaged with the input shaft gear (2) inner, high-speed position teeth. At the same time the range collar is slip splined to the rear output shaft (4). The rear output shaft (4) delivers the power flow to the rear propshaft (5). The position of the control actuator lever shaft (7) allows no clutch (6) engagement. The high/low range shift fork (8), is in the high-speed position on the control actuator lever shaft (7).

Scheme 147

In the 4HI mode, the power flow to the rear propshaft (10) is the same as it is in the 2HI mode. To deliver power flow to the front propshaft (13) during the 4HI position, the transfer control module commands the encoder motor (15) to apply the clutch to a calibrated torque. The encoder motor (15) turns the control actuator lever shaft (14). A brake in the encoder motor (15) holds the control actuator lever shaft (14) in the full clutch position. The control actuator lever shaft (14) is cam designed and the cam action moves the clutch lever (4). The clutch lever (4) pivots on the clutch lever pivot studs and moves toward the clutch apply plate, to engage the clutch. As more pressure is applied to the clutch apply plate, the clutch discs are compressed. Using inner clutch discs, which are engaged with the clutch hub (5), and the outer clutch discs, which are engaged with the clutch housing (6), the power flow is delivered to the clutch housing (6). The clutch hub (5) is splined to the rear output shaft (9), and the clutch housing (6) rotates on a needle bearing on the rear output shaft (9). The chain drive sprocket (7) is splined to the clutch housing (6). The power flows from the drive sprocket (7), through the chain (11), to the chain driven sprocket. The driven sprocket is splined to the front output shaft (12). The power flow is delivered to the front propshaft (13) through the front output shaft (12).

During the Auto 4WD mode, the power flow is the same as it is in the 4HI mode. Except, during the Auto 4WD mode, the encoder motor (15) rotates the control actuator shaft lever (14) to the correct torque level positions. Rotating the control actuator (14) to the various positions changes the clutch torque level. When a difference of front propshaft (13) to rear propshaft (10) speed is recognized, the transfer case control modules command for more, or less clutch torque.

Scheme 148

When shifting the transfer case to the 4LO mode, it commands the encoder motor (9) to turn the control actuator lever shaft (8), to move the high/low range shift fork (10). The shift fork (10) moves the high/low range collar (6), which is slip splined on the rear output shaft (7) toward the rear of the transfer case. The range collar (6) outer teeth disengage from the input shaft gear (2) inner teeth. The range collar (6) outer teeth then engage in the planetary carrier (5) teeth. The power flow is now from the input shaft gear (2) planetary teeth to the planetary gears (3) in the carrier. Rotating the planetary gears (3), which are engaged in the annulus gear (4), the planetary carrier (5) rotates. The planetary carrier (5) engaged to the range collar (6), drives the rear output shaft (7), providing a 2.72:1 reduction to the speed of the rear output shaft (7). The power flow to the front propshaft is the same as it is in the 4HI.

A neutral position is obtained when the range collar (6) is not engaged to the input shaft gear (2) or the planetary carrier (5). Neutral position is used for towing the vehicle.

Service 4WD Indicator: The Service 4WD indicator is an integral part of the cluster and cannot be serviced separately. This lamp is used to inform the driver of the vehicle that a transfer case system malfunctioned. The Service 4WD indicator is controlled by the transfer case shift control module via Class 2.

Transfer Case Encoder: The encoder is mounted to the transfer case motor/encoder assembly and is replaced as an assembly. The encoder converts the shift detent lever shaft position, representing a mode or range, into an electrical signal input to the transfer case shift control module. The module detects what position the transfer case is in by monitoring the voltage returned on the encoder signal circuit. This voltage translates into AUTO 4WD, 2HI, 4HI, NEUTRAL, and 4LO or in transition between gears.

Transfer Case Motor/Encoder: The transfer case motor/encoder consists of a permanent magnet (PM) DC motor and gear reduction assembly. It is located on the left hand side, driver's side, of the transfer case. When activated, it turns the shift detent lever shaft of the transfer case, clockwise or counterclockwise

to shift the transfer case. The motor/encoder is controlled with a pulse width modulated (PWM) signal by the transfer case shift control module. This circuit consists of a driver on both the Motor A and Motor B circuits. The encoder motor is bi-directional in order to allow the motor to shift the transfer case from 2HI or 4HI to NEUTRAL and 4LO positions.

Transfer Case Motor Lock: The transfer case motor lock is used to provide a 2HI, 4HI, and 4LO lock-up feature. When the lock circuit is energized, the transfer case encoder motor is allowed to turn. When the transfer case is placed 2HI, 4HI, or 4LO the motor lock circuit is de-energized and the lock is applied. This assures that the transfer case remains in the current gear position until a new gear position is requested. When AUTO is selected, the motor lock remains applied until an adaptive mode, torque being applied to the front propshaft, is required. During an adaptive mode the motor lock circuit is energized and the motor lock is released, enabling the encoder motor to turn and apply or release torque at the front propshaft.

Transfer Case Shift Control Module: The transfer case shift control module uses the VIN information for calculations that are required for the different calibrations used based on axle ratio, transmission, tire size, and engine. The system does not know which calibration to use without this information. When the vehicle is in the AWD mode, the transfer case shift control module monitors the speed of the front and rear propshaft, in order to detect wheel slippage. When wheel slippage is detected, the module applies a clutch pack contained inside the transfer case. This clutch pack is used to lock-in and apply the front propshaft, transferring torque to the front wheels. The clutch pack is applied by a motor/encoder assembly. When slip is no longer detected by the transfer case shift control module, the clutch is no longer applied.

Transfer Case Speed Sensors: There are three speed sensors on the automatic transfer case (ATC), two on the rear output shaft and one on the front output shaft. Each speed sensor is a permanent magnet (PM) generator. The PM generator produces a pulsing AC voltage. The AC voltage level and number of pulses increases as speed increases. Vehicle Speed Sensor - One of the two speed sensors on the rear output shaft is the vehicle speed sensor (VSS) 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. Rear Propshaft Speed Sensor - The transfer case shift control module converts the pulsating AC voltage from the rear transfer case speed sensor to a rear propshaft speed in RPM to be used for calculations. The rear propshaft speed can be displayed with a scan tool. Front Propshaft Speed Sensor - The transfer case shift control module converts the pulsating AC voltage from the front transfer case speed sensor to front propshaft speed in RPM to be used for calculations, and to monitor the difference between the front and rear sensor speed. It is also used in the AUTO, Adapt, mode to determine the amount of slip and the percent of torque to apply to the front axle. The front propshaft speed can be displayed with a scan tool.

Scheme 149

See also:
• LIFTING AND JACKING THE VEHICLE
• FASTENER NOTICE
• DIAGNOSTIC SYSTEM CHECK - Transfer Case
• TRANSFER CASE DESCRIPTION AND OPERATION