Transfer Case - Nvg 246-NP8: Overview GMC Sierra 3500

Test Description

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

1. 2: 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. 3: The presence of DTCs indicates that the transfer case shift control module has detected a fault. Go to symptoms for other concerns.
3. 4: 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. 5: 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. 6: 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.

Diagnostic System Check - Transfer Case

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

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

DTC B0790

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

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

DTC B2725

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

1. 2: This step tests to see if the malfunction is intermittent.
2. 3: This step tests the internal resistance of the propshaft speed sensor.
3. 4: This step tests to see if the propshaft speed sensor can generate a sufficient amount of AC voltage.
4. 5: This step tests the rear speed sensor low circuit for a short to ground, a high resistance, or an open.
5. 6: This step tests the rear speed sensor high circuit for a short to ground, a high resistance or an open.
6. 7: This step tests the rear speed sensor low circuit for a short to voltage.
7. 8: This step tests the rear speed sensor high circuit for a short to voltage.
8. 9: This step tests the rear speed sensor low circuit for a short to the rear speed sensor high circuit.

DTC C0300

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

1. 2: This step tests to see if the malfunction is intermittent.
2. 3: This step tests the internal resistance of the propshaft speed sensor.
3. 4: This step tests to see if the propshaft speed sensor can generate a sufficient amount of AC voltage.
4. 5: This step tests the front speed sensor low signal circuit for a short to ground, a high resistance, or an open.
5. 6: This step tests the front speed sensor high signal circuit for a short to ground, a high resistance or an open.
6. 7: This step tests the front speed sensor low signal circuit for a short to voltage.
7. 8: This step tests the front speed sensor high signal circuit for a short to voltage.
8. 9: This step tests the front speed sensor low signal circuit for a short to the front speed sensor high circuit.

DTC C0305

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

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

DTC C0306

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

1. 2: Listen for an audible click when the encoder motor brake operates. Command both the ON and OFF states. Repeat the commands as necessary.
2. 3: This step tests for voltage at the lock solenoid feed side of the encoder motor lock solenoid.
3. 4: This step verifies that the lock solenoid battery positive circuit is not shorted to power, shorted to ground, or have high resistance.
4. 5: This step determines if the encoder motor lock solenoid is faulty by checking the internal resistance.
5. 6: This step tests the control circuit of the encoder motor brake for a short to voltage or an open.
6. 7: This step determines if a corroded or damaged connector in the encoder motor harness is the cause.

DTC C0321

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

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

DTC C0327

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

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

DTC C0359

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

1. 2: This step determines if the rear propshaft speed sensor and wiring are operating properly.
2. 3: This step determines if the front propshaft speed sensor and wiring are operating properly.
3. 4: This step determines if the motor control A or motor control B circuits are shorted to ground within the encoder motor.
4. 5: This step tests the integrity of the motor windings.
5. 6: 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. 7: This step determines whether the transfer case is mechanically functioning properly.

DTC C0374

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

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

DTC C0379

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

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

DTC C0550

Symptoms - Transfer Case

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

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

Front Axle Will Not Engage

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

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

Front Axle Will Not Disengage

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

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

Transfer Case Shift Control Switch Inoperative

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

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.

No Correction for Slip in AWD Mode

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

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

Service Indicator Always On

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

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

Service Indicator Inoperative

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

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

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

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

1. 2: This step determines if the battery positive or ground circuits have an open or high resistance.
2. 3: This step helps to determine if the transfer case shift control module has the ability to command the encoder motor.
3. 4: This step determines if motor control A and motor control B circuits being shorted together is causing a shift block.
4. 5: This step determines if the motor control A and motor control B circuits are shorted together within the module.
5. 6: This step determines if a binding shift lever detent shaft is causing a shift block.
6. 7: This step has the transfer case removed and repaired.
7. 8: This step determines if the PNP switch is sending the correct range signal.
8. 9: This step replaces the transfer case shift control module.
9. 10: 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.
10. 11: This step replaced the encoder motor assembly.

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

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

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

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

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

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

Transfer Case Shift Control Switch Indicator Inoperative - One or More

General Operation

The New Venture Gear model NVG 246 RPO NP8 transfer case is a two speed automatic, active, transfer case. 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.

Scheme 22

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 3 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.

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

1. The oil pump suction pipe and screen will change to a one piece design.
2. The case half bolts will have a cup style washer and the bolt can be used again.
3. The clutch apply plate, clutch hub, and clutch oil restrictor plate will have a design change.
4. The 4 pinion gear planetary carrier assembly is changing to a 3 pinion gear design.

Scheme 23

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 24

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 25

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.