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Transfer Case - Nvg 263-NP1 (Selectable): Diagnosis GMC Sierra 2500

Transfer Case 2 illustrations ~4441 words

Diagnostic Starting Point - Transfer Case

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

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

Scan Tool Data List

The scan tool provides the following capabilities

  1. Displays the data list
  2. Displays current and history trouble codes
  3. Clears the diagnostic trouble codes after a repair is completed

Important: Ensure that the scan tool that you are using is functioning properly and has the latest software. Use of a malfunctioning scan tool or one that has old software can result in misdiagnosis and unnecessary parts replacement.

In order to use the scan tool, connect to the Data Link Connector (DLC) and turn the ignition switch to the RUN position.

The Transfer Case Scan Tool Data List contains all the automatic transfer case (ATC) related parameters that are available on the scan tool. The scan tool data list is arranged in alphanumeric order.

Use the Transfer Case Scan Tool Data List only after the following is determined

  1. A Diagnostic System Check has been completed.
  2. No Diagnostic Trouble Codes (DTCs) are 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 gear is in PARK or NEUTRAL.
  4. The accessories are OFF.

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 & POOR CONNECTIONS for further diagnosis.

Scheme 244

Scheme 244
Scheme 244

Scan Tool Data Definitions

The Automatic Transfer Case (ATC) Scan Tool Data Definitions contain a brief description of all ATC related parameters available on the scan tool. The list is in the order that the parameters appear on the scan tool.

Commanded Mode Indicator: The scan tool displays a range of 2WD to 4WD Low. This parameter indicates the current mode in which ATC is operating.

Encoder Circuit A: The scan tool displays On or Off. This parameter indicates whether transfer case shift control module is sensing voltage on the Encoder Circuit A (On=<1 volt, Off=>3 volts).

Encoder Circuit B: The scan tool displays On or Off. This parameter indicates whether transfer case shift control module is sensing voltage on the Encoder Circuit B (On=<1 volt, Off=>3 volts).

Encoder Circuit C: The scan tool displays On or Off. This parameter indicates whether transfer case shift control module is sensing voltage on the Encoder Circuit C (On=<1 volt, Off=>3 volts).

Encoder Circuit P: The scan tool displays On or Off. This parameter indicates whether transfer case shift control module is sensing voltage on the Encoder Circuit P (On=<1 volt, Off=>3 volts).

Encoder Gear Position: The scan tool displays a range of 2WD to 4WD Low. This parameter indicates the actual transfer case sector shaft position as sensed by the encoder.

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

Front Axle Switch 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.

GM Part Number: The scan tool displays an eight-digit number. This parameter indicates the transfer case shift control module GM software number.

Ignition 3: 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 its ignition feed.

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

Neutral Indicator Light: 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.

Park Switch: The scan tool displays Open or Closed. This parameter indicates the feedback states of the Park/Neutral Switch.

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.

Software ID: The scan tool displays a four-digit number. This parameter indicates the transfer case shift control module calibration version number.

Throttle Anticipation Mode: The scan tool displays Enabled or Disabled. This parameter changes from Disabled to Enabled when the vehicle starts movement from a stop position, light to heavy throttle is applied, and is currently in AWD mode. Throttle Anticipation Mode helps eliminate the clunking sound normally associated with front axle engagement.

TP (Throttle Position) Angle: The scan tool displays a range of 0-100 percent. The TP Angle is computed by the PCM from the TP sensor voltage. The TP Angle should read 0 percent at idle and 100 percent at Wide-Open Throttle (WOT).

2WD High Indicator Light: 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 Light: 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 Lamp Open: The scan tool displays Yes or No. This parameter indicates if the 4WD Lamp circuit is open or shorted to ground, when a Yes is displayed.

4WD Lamp Shorted: The scan tool displays Yes or No. This parameter indicates if the 4WD Lamp circuit is shorted to voltage or a loss of driver ground, when a Yes is displayed.

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.

Scheme 245

Scheme 245: Diagnostic Trouble Code (DTC) List
Scheme 245: Diagnostic Trouble Code (DTC) List

Circuit Description

The transfer case shift control switch consists of three normally open switches. The transfer case shift control module supplies a regulated 8 volts DC to the switch through the 8 volt reference circuit. The current travels through a 9.09 K ohms resistor located inside the switch. The switch returns current to the transfer case shift control module through the 4WD switch signal circuit.

The transfer case shift control module constantly monitors this signal voltage in order to determine the condition of the shift control switch circuit. If no buttons are pressed, and the transfer case shift control module detects a voltage level outside the possible range, approximately -0.5 to 1.0 volts, for longer than 5 minutes, the transfer case shift control module will set this DTC or if a button is held down or sticks for a period longer than 5 minutes.

When each of the switches is depressed they will complete a circuit through their own specific resistor. The transfer case shift control module continuously monitors the switch input to determine whether the 4HI, 2HI, and 4LO button selections are made by the driver. Neutral may be obtained if the following conditions are met

  1. The engine is running.
  2. The automatic transmission is in neutral or the clutch pedal is depressed on a manual transmission application.
  3. The vehicle speed is below (5 km/h) 3 mph.
  4. The transfer case is in the 2 HI mode.

Once these conditions have been met, pressing and holding both the 2 HI and 4 LO buttons for 10 seconds will shift the transfer case into neutral, turning on the red neutral indicator lamp.

Conditions for Setting the DTC

  1. The system constantly monitors the voltage on the 4WD switch signal circuit.
  2. If the system detects a voltage level outside the possible range produced when no buttons are depressed, approximately -0.5 to 1.0 volts, the DTC is logged.

Action Taken When the DTC Sets

  1. All shifting will be disabled.
  2. The SERVICE 4WD indicator lamp will be commanded on for the remainder of the current ignition cycle.

Conditions for Clearing the DTC

  1. The transfer case shift control module will clear the current DTC if the condition for setting the DTC no longer exists.
  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 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 4H, 2H, N, and 4L ranges.

This DTC detects a short to ground in the motor control A or motor control B circuit.

  1. The system will test the motor circuits: The system checks for unwanted voltage. The system supplies voltage on one circuit and reads the voltage back on the other.
  2. If the system detects a problem with the circuits, the DTC is logged.
  3. The transfer case shift control module senses a low voltage return in Motor Control A or Motor Control B when a high voltage is expected.
  1. All shifting will be disabled.
  2. The SERVICE 4WD indicator lamp will be commanded on 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 no longer exists.
  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 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 4H, 2H, N, and 4L ranges.

This DTC detects a short to voltage in the motor control A or motor control B circuits or a shorted motor.

  1. The system will test the motor circuits by reading the voltage on each circuit.
  2. If the system detects a problem with the circuits, the DTC is logged.
  3. The transfer case shift control module senses a high voltage in the motor control A or motor control B circuits when a low voltage is expected.
  1. All shifting will be disabled.
  2. The SERVICE 4WD indicator lamp will be commanded on 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 no longer exists.
  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 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 4H, 2H, N, and 4L ranges.

This DTC detects an open in the motor control A or motor control B circuits, or an open motor.

  1. The system will test 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 problem 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.
  1. All shifting will be disabled.
  2. The SERVICE 4WD indicator lamp will be commanded on 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 no longer exists.
  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 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 4H, 2H, N, and 4L ranges.

This DTC detects an open in the module ground circuit.

The system test the motor circuits

  1. The system checks for unwanted voltage.
  2. The system supplies voltage on each of the motor circuits and reads the voltage back on the other circuit.
  3. After the system checks for opens and shorts on the motor circuits, the system applies voltage through the motor and back to the module to ground.
  4. If the system detects a high voltage on the ground circuit, the DTC is logged.
  1. All shifting will be disabled.
  2. The SERVICE 4WD indicator lamp will be commanded on 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 no longer exists.
  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 transfer case encoder is a switch that converts a shaft position, representing a mode or range position, into electrical signals for use by the transfer case shift control module. The encoder houses 4 hall effect sensors that are used for channels P, A, B, and C. These sensors provide a path to ground, when a magnet, (part of the shift rail), passes over them.

The transfer case shift control module supplies an 8 volts reference and a ground circuit for the encoder hall effect sensors to function.

The transfer case shift control module supplies 5 volts on all the channels, thus as these channels are pulled to ground, the module can interpret the location of the transfer case shift position.

This DTC detects an open, short to ground, or a short to voltage (12 Volts) in the 8 volts reference circuit, an open in the signal ground circuit, an open, short to ground, or short to voltage (12 Volts) in the encoder signal circuits.

The transfer case shift control module reads back all high or low voltage on the encoder signal circuits.

  1. The transfer case shift control module will not allow any further mode or range shifts.
  2. The SERVICE 4WD indicator lamp will be commanded on 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 no longer exists.
  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 4WD low signal 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 transfer case shift control module problem, or a short to voltage on the 4WD low signal circuit.

  1. After the transfer case shift control module grounds the 4WD low signal circuit and reads back a high voltage, the DTC is set. The system will not attempt again during that ignition cycle.
  2. The transfer case shift control module reads back a high voltage when a low voltage is expected on the 4 low signal circuit.
  1. The transmission shift point may be affected.
  2. The SERVICE 4WD indicator lamp will be commanded on 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 no longer exits.
  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 front axle control circuit consists of an electric motor actuator which engages and disengages the front axle. The front axle actuator's motor consists of the following components within the actuator assembly

  1. A permanent magnetic (PM) motor
  2. A worm gear controlled plunger
  3. A front axle switch
  4. An electronic control circuit. The front axle actuator has 4 circuits connected to the actuator.
  5. The ignition 3 voltage circuit
  6. The ground circuit
  7. The axle actuator control circuit
  8. The axle switch signal circuit

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

This DTC detects a shorted actuator, or a short to 12 volt on the axle actuator control circuit.

  1. The system will try to engage the front axle. If the system cannot engage the front axle, the system will not attempt the procedure again during that ignition cycle.
  2. The transfer case shift control module reads back the front axle output as a high voltage when a low voltage is expected.
  1. All shifting for 4WD mode will be disabled.
  2. The SERVICE 4WD indicator lamp will be commanded ON 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 does not exist.
  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.

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

  1. EEPROM Checksum
  2. ROM Checksum
  3. RAM Checksum
  4. RAM Malfunction
  5. Relay Malfunction
  1. Critical operational parameters, stored in EEPROM, have failed the Checksum test, indicating invalid data.
  2. The masked ROM code has failed the Checksum test, indicating that masked the ROM data is no longer valid.
  3. The ROM code has failed the Checksum test, indicating that the ROM data is no longer valid.
  4. One or more ROM locations have failed the operational tests, indicating that some portions of RAM are not functional.
  5. The motor circuit test has indicated that one of the modules's relays is not able to make contact.

The SERVICE 4WD indicator lamp will be commanded on and the system will be disabled.

  1. Replace the transfer case shift control module.
  2. Perform the Transfer Case Diagnostic System Check.

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.

The transfer case shift control module does not receive a valid VIN digit for the correct application, K truck within 2 seconds after power up.

  1. The ignition counts since last fault will be cleared.
  2. The system will be disabled until valid VIN data is received.
  3. The SERVICE 4WD indicator lamp will be commanded on.

A history DTC will clear after a valid VIN digit is received.

Visual/Physical Inspection

  1. Inspect for aftermarket devices that could affect the operation of the automatic transfer case system. Refer to «CHECKING AFTERMARKET ACCESSORIES»(ref-175672-S27030348872005042500000) .
  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.

Symptom List

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

  1. See «Front Axle Will Not Engage»(ref-175704-S16356663702005042700000) .
  2. See «Front Axle Will Not Disengage»(ref-175704-S27747783512005042700000) .
  3. See «Transfer Case Shift Control Switch Inoperative»(ref-175704-S10851736482005042700000) .
  4. See «Service Indicator Always On»(ref-175704-S06553645352005042700000) .
  5. See «Service Indicator Inoperative»(ref-175704-S36151905442005042700000) .
  6. See «Transfer Case Shift Control Switch Indicator Always On - Two Or More»(ref-175704-S27168225012005042700000) .
  7. See «Transfer Case Shift Control Switch Indicators Flash Continuously»(ref-175704-S33555694772005042700000) .
  8. See «Transfer Case Shift Control Switch Indicator Inoperative - One Or More»(ref-175704-S36579157512005042700000) .
  9. See «Transfer Case Popping Noise»(ref-175704-S15110141982005042700000) .
  10. See «Transfer Case Whine Or Rumble Noise»(ref-175704-S21858734072005042700000) .
  11. See «Transfer Case Growl Or Grinding Noise»(ref-175704-S10266073922005042700000) .
  12. See «Transfer Case Clunk In 2 HI Only»(ref-175704-S04702190412005042700000) .
  13. See «Transfer Case Clunk In 4HI»(ref-175704-S33064590652005042700000) .
  14. See «Transfer Case Clunk In 4LO»(ref-175704-S12968207402005042700000) .
  15. See «Transfer Case Shudder Or Binding»(ref-175704-S32576893732005042700000) .
  16. See «Transfer Case Will Not Shift»(ref-175704-S00837372572005042700000) .
  17. See «Transfer Case Jumps Out Of Gear»(ref-175704-S40975706142005042700000) .
  18. See «Transfer Case Leak Diagnosis»(ref-175704-S03756738752005042700000) .

The front axle control circuit consists of an electric motor actuator which 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 all within the actuator assembly.

The front axle actuator has four circuits connected

  1. Ignition 3 voltage circuit
  2. Ground circuit
  3. Axle actuator control circuit
  4. Axle switch signal circuit

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

The front axle control circuit consists of an electric motor actuator which 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 all within the actuator assembly.

The front axle actuator has four circuits connected

  1. Ignition 3 voltage circuit
  2. Ground circuit
  3. Axle actuator control circuit
  4. Axle switch signal circuit

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

The transfer case shift control switch circuit consists of 3 normally open switches. The transfer case shift control module supplies a regulated 8 volts DC to the switch through the 8 volt-reference circuit. The current travels through a 9.09 K ohms resistor located inside the switch. Then switch returns current to the transfer case shift control module through the 4WD switch signal circuit.

The transfer case shift control module constantly monitors this signal voltage to determine the condition of the shift control switch circuit. The transfer case shift control module will set this DTC if any of the following conditions exist

  1. None of the buttons are pressed, and the transfer case shift control module detects a voltage level outside the possible range (approximately -0.5 to +1.0 volts) for more than 5 minutes
  2. A button is held down, or a button is stuck in the down position for a period more than 5 minutes

Each switch will complete a circuit through that switch's own specific resistor, when depressed. The transfer case shift control module continuously monitors the switch input to determine if the following button selections are made by the driver

  1. 4HI
  2. 2HI
  3. 4LO Neutral may be obtained if the following conditions are met
  4. The engine is running.
  5. The automatic transmission is in neutral, or the clutch pedal is depressed on a manual transmission application
  6. The vehicle speed is below 5 km/h (3 mph).
  7. The transfer case is in the 2HI mode.

Once these conditions have been met, press and hold both the 2HI and 4LO buttons for 10 seconds in order to shift the transfer case into neutral. The red neutral indicator lamp will illuminate.

The indicator circuits consist of four individual lamps contained inside the transfer case shift control switch. They are 2HI, 4HI, 4LO and NEUTRAL. The 2HI, 4HI, and 4LO indicators are contained inside their respective range button. The NEUTRAL indicator is located on the front panel of the switch. When the ignition is ON, the transfer case shift control module illuminates the indicator 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 after a shift has been requested, and will continue to flash until the transfer case shift control module can complete the shift.

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, it waits for the action to take place before the gear change is made. While waiting, the shift control switch indicator will continue to flash for a period of time, at which time all other mode requests will be 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 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 has four circuits connected

  1. Ignition 3 voltage circuit
  2. Ground circuit
  3. Axle actuator control circuit
  4. Axle switch signal circuit

Whenever 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 indicator lamps circuit consist of four individual indicators contained inside the transfer case shift control switch. They are 2HI, 4HI, 4LO and Neutral. The 2HI, 4HI, and 4LO indicators are contained inside their respective range button. When the ignition in ON, the transfer case shift control module illuminates the indicator 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 after a shift has been requested and will continue 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 indicators. The solid state circuit also receives voltage whenever the headlamp switch is in the parklamp or headlamp position. When the solid state circuit receives voltage from the headlamp switch, the circuit will reduce the voltage supplied to the indicators, dimming the indicators when the headlamps are ON.

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