NVG 243-NP1 (Two Speed Selectable)

The transfer case is used to provide power flow from the transmission to the front axle. The transfer case also provides a way of disconnecting the front axle in order to provide better fuel economy and quieter operation when the vehicle is driven on the roads where the four-wheel drive is not required. The transfer case provides an additional gear reduction when placed in low range. This is useful when difficult off-road conditions are encountered.
The New Venture Gear Model NV243 transfer case is used on all of the four-wheel drive vehicles under 9200 lbs. GVW.
The Model NV243 has an aluminum case, chain driven units with four modes of operation; neutral, two wheel drive high range, four wheel drive high range, and four wheel drive low range. The gear reduction for low range is provided by a planetary gear set.
A floor mounted shift lever is used in order to select the operating range for the NV241. The indicator lamps on the floor console show the current mode of operation. When four-wheel drive indicator lamp is designed to come ON whenever the front axle has engaged. A slight delay for the front axle indicator lamp to come ON is normal.
The New Venture Gear Model NV243 is electronically actuated. The vehicles equipped with this model have no transfer case selector lever. The operator selects 2HI, 4HI, or 4LO by pushing one of three switches mounted on the instrument panel. During normal driving the transfer case is in the 2HI mode. When the transfer case is in 2HI both the 4H1 and the 4L0 switch circuits are open, and both lights are OFF. When the four-wheel drive has been selected, the four-wheel drive indicator lamp on the switch turns on when the front axle has engaged.
The lamp will blink while the front axle is engaging. For more information on the electrical operation of the NV243, refer to Transfer Case System Description.

Two-Wheel Drive Operation
When the transfer case is in the 2 WHEEL range, the torque flows from the input gear to the range shift hub and the main shaft, through the propeller shaft to the rear axle.

2HI to 4HI

Important: Shifting into the 4HI range causes the following conditions to occur.

1. The front axle indicator lamp does not come on until the front axle engages.
2. The torque flows from the input gear to the mainshaft the same as in the two-wheel position.
The shift linkage moves the mode synchronizer sleeve into engagement with the clutch teeth of the drive sprocket. This locks the drive sprocket to the mainshaft through the synchronizer sleeve.
3. The torque is transmitted through the drive sprocket and the drive chain to the driven sprocket and the output shaft. The torque then flows through the front propeller shaft to the front axle.
4. The shift mechanism in the transfer case closes the transfer case switch.
The current is then applied to the front axle electro-mechanical actuator and the front axle switch. In the K30 vehicles, the power is also supplied by the transfer case relay to the transfer case synchronizer.
5. The front axle shift mechanism, when fully engaged, closes a switch, causing the front axle indicator lamp to come ON.
6. If the shift lever is moved back to the 2 WHEEL position, the operations in the preceding steps are reversed. The current to the thermal actuator is turned OFF. The gas cools and the piston retracts allowing the shift fork in the front axle in order to return to the two-wheel drive position.

Four-Wheel Drive Low Range Operation
When the transfer case is shifted into the 4LO position, the torque flow and the operation is similar to the 4HI range, except that the range shift hub engages the planetary carrier. The planetary gear set then provides a gear reduction to the front and the rear axles.

Identification
For New Venture Gear Transfer Cases, an identification tag is attached to the rear case half. The tag provides the transfer case model number, the low range reduction ratio, and the assembly part number.

Transfer Case System Description
The New Venture Gear Model NV243 is an electronically controlled optional transfer case for use on four wheel drive K trucks. The driver selects 2HI, 4HI, or 4LO by pushing one of three illuminating shift select buttons mounted on the instrument panel. The shift select buttons display the transfer case mode and range, self-test, diagnostic trouble codes, and electronic shift mechanical engaging problems. During normal driving the transfer case is in the 2HI mode. When the transfer case is in the 2HI mode. When the transfer case is in 2HI both the 4HI and 41_0 switch circuits are open, and both lights are OFF. When the four-wheel drive shift select button has been pressed, the four-wheel drive indicator lamp under the sift select button turns ON when the front axle has engaged. The shift select button will blink while the front axle is engaging. This is a normal condition. The shifting of the transfer case is performed by a motor/encoder that receives drive signals from the Transfer Case Control Module (TCCM). When the driver selects one of the transfer case shift select buttons, request signals are sent to the TCCM. If the correct input signals exists, the TCCM will send drive voltages to the motor/encoder. The motor/encoder will position the transfer case to the ordered shift position.

Mode Shifts
The mode shifts are shifts from 2HI to 4HI and 4HI to 2HI. A mode shift can be accomplished in any gear position and at any vehicle speed. If the system is in 2HI, the driver can shift into 4HI merely by pressing the 4HI shift select button. The 4HI button will blink status whenever a 2HI or 4HI shift is initiated and will continue to blink until the TCCM completes the shift. After the shift into 4HI is accomplished, the 4HI status lamp remains lit to indicate that the system is in 4HI.
There is a difference between when the TCCM sends voltage signals in order to engage a four wheel drive shift and when the vehicle is truly in four wheel drive. The transfer case can be shifted into 4HI and the front axle may not be engaged.
The driver can shift from 4HI back to 2HI by pressing the 2HI shift select button. The 2HI shift select button blinks until the shift to 2HI is complete. The 2HI shift select button will remain on once the shift is mechanically complete.

Range Shifts
1. The range shifts are the shifts between the HI and the LO ranges.
^ 2HI to 4LO
^ 4HI to 4LO
^ 4LO to 4HI
^ 4LO to 2HI

2. A range shift can only be made with the automatic transmission in neutral or with the manual transmission clutch fully depressed. The shift occurs when the vehicle speed is below three miles per hour.
Whenever a shift into 4LO is initiated, the 4LO shift select button blinks. The 4LO shift select button will continue to blink until the shift is completed mechanically or until 30 seconds elapses. The 4LO shift select button must be on and not blinking prior to shifting the transmission into gear or releasing the clutch pedal.
If a range shift is initiated when the transmission is engaged or the vehicle speed is above 3 mph, the 4LO shift select button will blink for 30 seconds and no range shift actually occurs, the TCCM will default and position the transfer case into 4HI.

Transfer Case Control Module Description
1. The TCCM performs the following functions:
^ Receives input signals
^ Processes the signal information
^ Develops output signals
^ Sends the output signal in order to control the shifting of the transfer case

2. The TCCM receives input signals from the following sources:
^ The transfer case shift select buttons
^ The NSBU switch on the vehicles with automatic transmissions
^ The clutch position switch on the vehicles with manual transmissions
^ The vehicle sped sensor calibrator module
^ The encoder/motor range and the mode feedback signals
^ The diagnostic enable
^ The front axle mechanical status signal

3. In order to ensure the electronic shift system is operating properly, the transfer case control module (TCCM) continually performs diagnostics checks on itself and other parts of the electronic shift system when the ignition switch is in the run position. The following are different types of system checks that the TCCM continually performs.

RAM/ROM Check
The TCCM compares the current internal operating program with a stored operating program. This comparison allows the TCCM in order to evaluate if the TCCM's RAM and ROM are operating properly. Should the TCCM detect a problem with the internal operating program, a diagnostic trouble code (DTC) of 4 is stored indicating the TCCM memory is damaged. Replace the TCCM. Refer to Transfer Case Control Module Description.

Data Memory Retention Check
The TCCM checks the stored diagnostic trouble code memory to see if the memory has changed since the ignition switch was last positioned to OFF. This self test checks in order to see if the RAM standby power supply has been interrupted. If the TCCM detects a RAM standby power supply interruption, (the loss of stored diagnostic trouble code) the TCCM stores a DTC of 1 indicating RAM standby power failure.
This condition occurs when the TCCM is disconnected from the wiring harness or battery power is removed. The DTC of 1 automatically clears from the TCCM after cycling the ignition switch ON and OFF five times.

Encoder Signal Check
The TCCM checks the encoder signal in order to verify that the transfer case is in either 2HI, 4HI, or 4LO.

Encoder Switch Monitor Check
While the transfer case shifts, the encoder within the electric-shift motor is monitored for the proper operating sequence. If during a shift, the encoder changes to an incorrect position, an error counter in the TCCM starts to count the number of times the encoder fails. If the encoder fails eight times, the TCCM produces a DTC of 2 indicating an Encoder Fault. When this happens, the TCCM outputs a signal in order to default the rail shift pattern in the encoder in order to allow for only shifts into 2HI and 4LO.
In order to protect against transient, random encoder faults caused by vibration, contamination, electrical noise, etc., the error counter reduces the count by one each time a good encoder value is detected. The encoder must fail 25 percent of the time for the TCCM to store a DTC of 2 and indicate a damaged encoder.

Motor and Relay Voltage Checks
Whenever the electric-shift motor is turned ON or OFF the motor and the electrical circuits are tested both in the de-energized and energized condition. If one or both voltage relays fail to detect the proper voltage after energizing or de-energized and energized condition. If one or both of the voltage relays fail to detect the proper voltage after energizing or de-energizing, the shift is aborted by the TCCM and a DTC of 3 is stored in order to indicate a faulty TCCM motor circuit.
If one or both relays fail to detect the proper voltage after de-energizing, both relays are turned ON by the TCCM, (even with the ignition switch positioned OFF) in order to prevent the motor from running. The TCCM then stores a DTC of 3 in order to indicate a faulty TCCM motor circuit. All of the status lamps blink three times, stop, and repeat the blinking continuously in order to alert the driver that the electronic shift system requires immediate repair. The battery will drain when this condition occurs, regardless of the ignition switch position.

Motor/Encoder Circuit Operation
The TCCM operates the motor/encoder in one direction by energizing one relay while the second relay is de-energized. The TCCM operates the motor in the reverse direction by energizing the second relay while the first relay is de-energized. The encoder part of the motor/encoder sends shift positioning signals to the TCCM.
The motor/encoder converts a shaft position, representing a mode of range selection, into electrical signals for use by the TCCM. By interpreting the four channels (P, A, B, C) of the encoder, the transfer case control module can detect what position the transfer case is in 2HI, 4HI, 4LO, or in transition between any of the two.
The four hall effect sensors of the motor/encoder are used for channels (A, B, C, and P). These sensors provide a path to ground when a magnet passes over them. A rotating magnetic ring causes the hall effect sensors voltage to drop from 5 to 0 volts. The TCCM detects the voltage of all the channels and interprets the current transfer case shift position.