Transfer Case (NVG126-NP4): Overview Oldsmobile Bravada III

Test Description

The number(s) below refer to the step number(s) on the diagnostic table.

1. 2. Lack of communication 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 will determine 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 will compile 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 DTCs P0502 and P0503 first.
5. 6. Perform diagnostics for DTC C0300 and C0305 first before addressing other DTCs. DTC C0300 and C0305 can be responsible for setting other DTCs.

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

1. 2. Tests to see if the malfunction is intermittent.
2. 3. Tests the internal resistance of the propshaft speed sensor.
3. 4. Tests to see if the propshaft speed sensor can generate a sufficient amount of AC voltage.
4. 5. Tests the RSS LO circuit for a short to ground, a high resistance, or an open.
5. 6. Tests the RSS HI circuit for a short to ground, a high resistance, or an open.
6. 7. Tests the RSS LO circuit for a short to voltage.
7. 8. Tests the RSS HI circuit for a short to voltage.
8. 9. Tests the RSS LO circuit for a short to the RSS HI circuit.

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

1. 2. Tests to see if the malfunction is intermittent.
2. 3. Tests the internal resistance of the propshaft speed sensor.
3. 4. Tests to see if the propshaft speed sensor can generate a sufficient amount of AC voltage.
4. 5. Tests the FSS LO circuit for a short to ground, a high resistance, or an open.
5. 6. Tests the FSS HI circuit for a short to ground, a high resistance, or an open.
6. 7. Tests the FSS LO circuit for a short to voltage.
7. 8. Tests the FSS HI circuit for a short to voltage.
8. 9. Tests the FSS LO circuit for a short to the FSS HI circuit.

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

1. 2. Tests the motor circuit for a current malfunction.
2. 3. Helps isolate motor malfunctions from the transfer case shift control module and wiring.
3. 4. Test for an open, high resistance, short to ground, or short to voltage.

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

1. 2. Tests the encoder circuit for a current malfunction.
2. 3. Tests for an internal encoder malfunction which is present only in certain areas of the encoder sensor.
3. 4. Tests for proper reference voltage at the encoder.
4. 5. Tests the 5 V Reg. Encoder Circuit for a short to voltage, short to ground, an open or high resistance.
5. 6. After determining that the reference voltage measured in Step 4 was correct, Step 6 reviews the reading originally measured in Step 3 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.
6. 7. Tests the Encoder Signal circuit and the Encoder Return circuit for a short to voltage.
7. 8. Helps determine a faulty encoder.
8. 9. Tests the Encoder Signal circuit and the Encoder Return circuit for an open or a short to ground.

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

1. 2. Determines if the Rear Propshaft Speed Sensor and wiring are working properly.
2. 3. Determines if the Front Propshaft Speed Sensor and wiring are working properly.
3. 4. Helps determine if the DTC set due to a mechanical or an electrical failure.
4. 5. Tests the integrity of the Motor Feed circuits.
5. 6. Determines whether the transfer case is mechanically functioning properly.

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

1. 2. Replacement of the transfer case shift control module.

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Symptoms - Transfer Case

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

1. 2. Determines whether the failure is the result of a malfunctioning transfer case shift control module or the instrument cluster.

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

1. 2. Determines whether the failure is the result of a faulty transfer case shift control module or the instrument cluster.

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Transfer Case Description and Operation

The New Venture Gear model NVG 126 RPO NP4 transfer case is a one speed automatic, active, transfer case. The NVG 126 provides only one mode, Auto 4WD, and is transparent to the operator. The active transfer case 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 pre-load 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 0-7 N.m (0-62 lb in) of clutch torque during low speed, low engine torque operation, and predetermined higher torque for 32 km/h (20 mph) and greater. This prevents crop-hop and binding at low speeds, and provides higher torque biases at higher vehicle speeds, to enhance stability. Above 32 km/h (20 mph), both the rear propshaft and the front propshaft are driving the vehicle.

The NVG 126 requires no clutch shimming. The transfer case control module controls the clutch wear and 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 126 case halves are high-pressure die-cast aluminum. Ball bearings support the input shaft gear, the front output shaft, and the rear output shaft. A needle 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 to prevent warpage.

The transfer case requires Auto Trac II Fluid GM P/N United States 12378508, GM P/N Canada 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.

To drive the rear propshaft (5), the power flows from the transmission to the input shaft gear (1). The input shaft gear (1) is splined to the rear output shaft (2). The power flows from the rear output shaft (2) to the rear propshaft (5).

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To drive the front propshaft (8), the clutch hub (3) is splined to the rear output shaft (2). When the transfer case control module commands for more or less clutch torque, the encoder motor (7) turns the control actuator lever shaft (6). The control actuator lever shaft (6) is cam designed, and the cam action moves the clutch lever (4). The clutch lever (4) pivots on the control lever studs and moves toward the clutch apply plate to increase clutch torque. 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 outer clutch discs, which are engaged with the clutch housing, the power flow is delivered to the clutch housing. The chain drive sprocket is splined to the clutch housing. The power flows from the drive sprocket through the chain (9), to the chain driven sprocket. The driven sprocket is splined to the front output shaft (8). The power flow is delivered to the front propshaft through the front output shaft (8).