Transfer Case (NVG226-NP8): 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. Look for the visual operation of the AWD Indicator. Command both the ON and OFF states.
2. 3. Helps determine if there is proper voltage supplied to the transfer case select switch.
3. 4. Helps determine if there is a short to ground in the indicator control circuit.
4. 5. Helps determine if there is an open in the indicator control circuit.
5. 6. Tests the indicator feed circuit for an open or high resistance.
6. 7. Tests the AWD Indicator control circuit for a short to ground.
7. 8. Tests the AWD Indicator control circuit for an open or high resistance.

Scheme 53

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

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

Scheme 54

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

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

Scheme 55

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

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

Scheme 56

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

1. 2. Look for the visual operation of the Neutral Indicator. Command both the ON and OFF states.
2. 3. Tests for voltage at the Neutral Indicator Feed side of the transfer case select switch.
3. 4. Verifies that the transfer case shift control module is providing ground to the Neutral Indicator.
4. 5. Tests if ground is constantly being applied to the Neutral Indicator.
5. 6. Tests the control circuit of the neutral indicator for a short to voltage or an open.
6. 7. Tests the control circuit of the neutral indicator for a short to ground.

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Scheme 58

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

1. 2. Tests for proper operation of the transfer case mode select switch.
2. 3. Tests for proper voltage supply to the mode switch.
3. 4. Tests the mode switch for proper resistance values in all mode switch states.
4. 5. Tests the switch signal circuit for a short to voltage.
5. 6. Tests the switch signal circuit for a short to ground.
6. 7. Tests the switch signal circuit for an open.
7. 8. Tests the switch signal circuit for a short to the 5 V Reg circuit.
8. 9. Determines whether the 5 V Reg circuit is greater than or less than specified voltage.
9. 10. Tests the 5 V Reg circuit for a short to voltage.
10. 11. Tests the 5 V Reg circuit for a short to ground.
11. 12. Tests the 5 V Reg circuit for an open.

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Scheme 60

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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Scheme 64

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.

Scheme 65

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. Tests for voltage at the Brake Feed side of the encoder motor brake.
3. 4. Verifies that the transfer case shift control module is providing ground to the encoder motor brake.
4. 5. Tests if ground is constantly being applied to the encoder motor brake.
5. 6. Tests the control circuit of the encoder motor brake for a short to voltage or an open.
6. 7. Tests the control circuit of the encoder motor brake for a short to ground.

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Scheme 67

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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Scheme 69

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

1. 2. Tests for proper reference voltage to the transfer case shift control module on the 4WD LO circuit.
2. 3. Tests the 4WD LO circuit for a short to voltage.
3. 4. Tests the 4WD LO circuit for an open or high resistance.
4. 5. Repairs the 4WD LO circuit for a short to voltage.

Scheme 70

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

1. 2. Helps determine if the DTC set due to a mechanical or an electrical fault.
2. 3. Tests the integrity of the Motor Feed circuit.
3. 4. Determines whether the Encoder Motor is moving to the proper position.

Scheme 71

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

1. 2. Tests the front axle circuit for a current malfunction.
2. 3. Helps determine if the failure is the result of a short to voltage or ground.
3. 4. Helps determine if the front axle control circuit is shorted to ground.
4. 5. Tests the integrity of the front axle switch and battery feed circuits.
5. 6. Tests the front axle control circuit for short to ground.
6. 7. Tests the front axle switch circuit for short to voltage.
7. 8. Tests the front axle battery feed circuit and the front axle switch circuit for an open or short to ground.
8. 9. Tests the front axle control circuit and the front axle ground circuit for an open or high resistance.

Scheme 72

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

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Scheme 75

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

1. 2. Tests the electrical function of the front axle actuator. Helps determine between mechanical and electrical malfunctions.
2. 3. Tests for proper power and ground at the front axle actuator.
3. 4. Tests the operation of the front axle control circuit.
4. 5. Tests the electrical function of the front axle actuator control circuit.
5. 6. Tests for proper supply voltage to the front axle actuator.
6. 7. Tests for open fuse in the front axle feed circuit.
7. 8. Tests the front axle control circuit for an open or high resistance.
8. 9. Tests the front axle switch circuit for an open or high resistance.
9. 10. Helps determine if the front axle actuator has a mechanical malfunction.
10. 11. Tests the front axle switch circuit for a short to voltage.
11. 12. Inspect the front axle for a mechanical malfunction.

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Scheme 77

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

1. 2. Tests the functionality of the Mode/Range buttons.
2. 3. Tests the modules ability to operate the transfer case modes.

Scheme 78

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

1. 2. Helps determine whether the front axle switch is functioning properly.
2. 3. Helps determine whether the front axle switch is locking and unlocking.
3. 4. Tests transfer case clutch performance.

Scheme 79

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

1. 2. Tests the transfer case electrical control of the lamp circuits.
2. 3. Helps determine a short to ground in the suspect lamp circuit(s).
3. 4. Test the suspect lamp circuit(s) for a short to ground.
4. 5. Repair short to ground in the suspect lamp circuit.

Scheme 80

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

1. 2. Helps to determine if the fault is due to a faulty transfer case shift module, encoder/motor assembly, or the brake control circuit.
2. 3. Replace a faulty transfer case shift control module.
3. 4. Tests the T-Case Lock circuit for an open, short to ground, or short to voltage.
4. 5. Replace a faulty encoder/motor assembly.

Scheme 81

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

1. 2. Determine the position of the Front Axle Switch.
2. 3. Helps determine if the front axle will not engage.
3. 4. Helps determine if the front axle will not disengage.

Scheme 82

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

1. 2. Tests the transfer case electrical control of the lamp circuits.
2. 3. Helps determine module failures.
3. 4. Tests the effected lamp circuit for an open or high resistance.
4. 5. Tests the lamp feed circuit for an open or short to ground.

Scheme 83

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.

Scheme 84

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 226 RPO NP4 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 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 in the Auto 4WD mode. 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 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.

Scheme 95

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 96

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 97

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.