Transfer Case - Nvg 226-NP8: Overview GMC Envoy II

Transfer Case Control Schematic Icons

Transfer Case Control Schematic Icons Icon Icon Definition IMPORTANT: Twisted-pair wires provide an effective shield that helps protect sensitive electronic components from electrical interference. If the wires were covered with shielding, install new shielding. In order to prevent electrical interference from degrading the performance of the connected components, you must maintain the proper specification when making any repairs to the twisted-pair wires shown : The wires must be twisted a minimum of 9 turns per 31 cm (12 in) as measured anywhere along the length of the wires. The outside diameter of the twisted wires must not exceed 6.0 mm (0.25 in)

Scheme 1

Scheme 2

Scheme 3

Scheme 4

Scheme 5

Scheme 6

Scheme 7

Scheme 8

Test Description

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

1. 2: This step looks for the visual operation of the AWD indicator. Command both the ON and OFF states.
2. 3: This step helps determine if proper voltage is supplied to the transfer case select switch.
3. 4: This step helps determine if there is a short to ground in the indicator control circuit.
4. 5: This step helps determine if there is an open in the indicator control circuit.
5. 6: This step tests the indicator feed circuit for an open or high resistance.
6. 7: This step tests the AWD indicator control circuit for a short to ground.
7. 8: This step tests the AWD indicator control circuit for an open or high resistance.

DTC B0770

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

1. 2: This step looks for the visual operation of the 4HI indicator. Command both the ON and OFF states.
2. 3: This step helps determine if proper voltage is supplied to the transfer case select switch.
3. 4: This step helps determine if there is a short to ground in the indicator control circuit.
4. 5: This step helps determine if there is an open in the indicator control circuit.
5. 6: This step tests the indicator feed circuit for an open or high resistance.
6. 7: This step tests the 4HI neutral control circuit for a short to ground.
7. 8: This step tests the 4HI neutral control circuit for an open or high resistance.

DTC B0775

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

1. 2: This step looks for the visual operation of the 4LO indicator. Command both the ON and OFF states.
2. 3: This step helps determine if proper voltage is supplied to the transfer case select switch.
3. 4: This step helps determine if there is a short to ground in the indicator control circuit.
4. 5: This step helps determine if there is an open in the indicator control circuit.
5. 6: This step tests the indicator feed circuit for an open or high resistance.
6. 7: This step tests the 4LO neutral control circuit for a short to ground.
7. 8: This step tests the 4LO neutral control circuit for an open or high resistance.

DTC B0780

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

1. 2: This step looks for the visual operation of the 2HI indicator. Command both the ON and OFF states.
2. 3: This step helps determine if proper voltage is supplied to the transfer case select switch.
3. 4: This step helps determine if there is a short to ground in the indicator control circuit.
4. 5: This step helps determine if there is an open in the indicator control circuit.
5. 6: This step tests the indicator feed circuit for an open or high resistance.
6. 7: This step tests the 2HI neutral control circuit for a short to ground.
7. 8: This step tests the 2HI neutral control circuit for an open or high resistance.

DTC B0785

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

1. 2: This step looks 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 propshaft speed sensor low circuit for a short to ground, a high resistance or an open.
5. 6: This step tests the rear propshaft speed sensor high circuit for a short to ground, a high resistance or an open.
6. 7: This step tests the rear propshaft speed sensor low circuit for a short to voltage.
7. 8: This step tests the rear propshaft speed sensor high circuit for a short to voltage.
8. 9: This step tests the rear propshaft speed sensor low circuit for a short to the rear propshaft 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 propshaft speed sensor low signal circuit for a short to ground, a high resistance or an open.
5. 6: This step tests the front propshaft speed sensor high signal circuit for a short to ground, a high resistance or an open.
6. 7: This step tests the front propshaft speed sensor low signal circuit for a short to voltage.
7. 8: This step tests the front propshaft speed sensor high signal circuit for a short to voltage.
8. 9: This step tests the front propshaft speed sensor low signal circuit for a short to the front propshaft 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 tests 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 encoder motor brake solenoid for an internal short to ground.
6. 7: This step tests the control circuit of the encoder motor brake for a short to voltage or an open.
7. 8: 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 tests 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 that the reference voltage measured in Step 4 was correct, Step 6 reviews the reading originally measured in Step 3 to see if it was higher or lower than what should have been 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 LO circuit for a short to voltage.
3. 4: This step tests the 4WD LO circuit for an open or high resistance.
4. 5: This step repairs the 4WD LO 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 operating 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 short to voltage or ground.
7. 8: This step tests the front axle switch signal circuit for a short to voltage.
8. 9: This step tests the front axle ignition 3 voltage circuit and the front axle switch circuit for an open or short to ground.
9. 10: This step tests the front axle control circuit and the front axle ground circuit for an open or high resistance.

DTC C0379

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 between 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 between 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 an 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 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 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 circuit have an open or high resistance.
2. 3: This step helps to determine if the fault is due to a faulty transfer case shift module, encoder/motor assembly, or the brake control circuit.
3. 4: This step replaces a faulty transfer case shift control module.
4. 5: This step tests the T-Case Lock circuit for an open, short to ground or short to voltage.
5. 6: This step replaces a faulty 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

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

General Operation

The New Venture Gear model NVG 226 RPO NP8 transfer case is a two speed automatic, active, transfer case. The NVG 226 provides five modes, Auto 4WD, 4 HI, 4 LO, 2 HI 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 lb ft of clutch torque during low speed, low engine torque operation, and predetermined higher torque for 32 km/h (20 mph) and greater. This prevents crow-hop and binding at low speeds and provides higher torque biases at higher vehicle speeds, to enhance stability.

The NVG 226 requires no clutch shimming. The transfer case control module controls for the wear of the clutch and different clutch torque levels. The software learns adapt ready positions, which are for the correct clutch torque. The learned adapt ready positions vary as the unit wears over its life.

The NVG 226 case halves are high-pressure die-cast aluminum. 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 clutch discs have friction material on one side only, to prevent warpage. 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.

Scheme 9

When the NVG 226 is in the 2 HI mode, the power flows from the transmission to the input shaft gear (1). The input shaft gear (1) is connected to the rear output shaft (5) by the high/low range collar (2). The range collar (2) inner teeth, high-speed, are engaged with the input shaft gear (1) high-speed position teeth. At the same time the range collar is slip splined to the rear output shaft (5). The rear output shaft (5) delivers the power flow to the rear propshaft (6). The position of the control actuator lever shaft (8) allows no clutch engagement. The shift detent lever (7), which moves the shift rail and shift fork (10), is in the high-speed position on the control actuator lever shaft (8).

Scheme 10

In the 4 HI mode, the power flow to the rear propshaft is the same as it is in the 2 HI mode. To deliver power flow to the front propshaft during the 4 HI position, the transfer control module commands the encoder motor to apply the clutch to a calibrated torque. The encoder motor turns the control actuator lever shaft (8). A brake in the encoder motor holds the control actuator shaft (8) in the full clutch position. The control actuator lever shaft (8) is cam designed and the cam action moves the clutch lever (4). The clutch lever (4) pivots on the control 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 (3), and the outer clutch discs, which are engaged with the clutch housing, the power flow is delivered to the clutch housing. The clutch hub (3) is splined to the rear output shaft (5), and the clutch housing rotates on a needle bearing on the rear output shaft (5). The chain drive sprocket is splined to the clutch housing. The power flows from the drive sprocket, through the chain, to the chain driven sprocket. The driven sprocket is splined to the front output shaft (9). The power flow is delivered to the front propshaft through the front output shaft (9).

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

Scheme 11

When shifting the transfer case to the 4 LO mode, it commands the encoder motor to turn the control actuator lever shaft (8), to move the shift detent lever (7), and to apply the clutch. The shift detent lever (7) moves the shift rail and the spring dampened shift fork (10). The shift fork (10) moves the high/low range collar (2) on the rear output shaft (5) splines toward the rear of the transfer case. The range collar (2) inner teeth, high speed, disengage from the input shaft gear (1) high speed teeth. The range collar (2) outer teeth, low speed, then engage in the planetary carrier teeth. The power flow is now from the input shaft gear (1) planetary teeth to the planetary gears in the carrier. Rotating the planetary gears, which are engaged in the annulus gear, the carrier rotates. The carrier, that is engaged to the range collar, then drives the rear output shaft. Therefore, providing a 2.69:1 reduction to the speed of the rear output shaft. The power flow to the front propshaft is the same as it is in the 4 HI.

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

Scheme 12

The NVG 226 transfer case features a rotary 4 mode 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 turn 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 226 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 funning.
2. The automatic transmission is in Neutral.
3. The vehicle speed is less than 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 less than 5 km/h (3 mph).
4. The transfer case is in 2HI mode.

Once these conditions have been met, turn the rotary switch clockwise past the last and hold for 10 seconds. When the system completes the shift to neutral, the red neutral lamp will illuminate.

Scheme 13

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 propshafts in order to detect wheel slippage. When wheel slippage is detected, the module applies a clutch pack contained in side 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.

Scheme 14

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 (drivers side) of the transfer case. When activated it turns the sector shaft of the transfer case (clockwise or counter clockwise) to shift the transfer case. The 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 to allow the motor to shift the transfer case from 2HI or 4HI to NEUTRAL and 4LO positions.