Transfer code c0308

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https://haynes.com/en-us/tips-tutorials/2007-13-chevy-silveradogmc-sierra-truck-routine-maintenance-faq


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Which of these does your vehicle have
Transfer Case - NVG 126-NP4
Transfer Case - NVG 226-NP8
Do you know what a RPO code is ? Where it's located on the vehicle ? RPO code NP4 or NP8 will tell you which transfer case your's has . Vacuumn has nothing to do with it . controlled electroniclly . Having a professional scan tool hooked up an DTC'S - diagnostic trouble codes check is what you should do .

The production/process codes provide the description of the Regular Production Options (RPOs) used on the vehicle. The RPO list is printed on the Service Parts Identification Label. The following is a list of the RPO abbreviations and the description of each:
NP4
Transfer Case Active Single Speed All Wheel Drive (AWD)
NP5
Steering Wheel Leather Wrapped
NP7
Steer Column EEC Approved
NP8
Transfer Case Active All Wheel Drive (AWD) 2 Speed

SERVICE 4WD indicator
The SERVICE 4WD indicator is an integral part of the cluster and cannot be serviced separately. This lamp is used to inform the driver of the vehicle that a transfer case system malfunction. The SERVICE 4WD indicator is controlled by the transfer case shift control module via Class 2.

Does your vehicle have three or four button shift switch ?
The NVG 236 transfer case features a 4 button shift control switch located on the instrument panel.
OR
The NVG 233 transfer case features a 3 button shift control switch,
The transfer case shift control module is equipped with the ability to store diagnostic information, which is useful to a technician in the event of module, component or wiring failures. This information can be retrieved from the transfer case shift control module by way of flash codes, which are displayed on the three transfer case shift control switch buttons. These buttons are located on the instrument panel to the right of the steering wheel Before obtaining DTCs, perform the following transfer case control module (TCCM) Self-Test.
TCCM Self-Test
Observe the transfer case shift control switch indicators while turning the ignition switch to RUN. A properly operating system will flash all indicators and then will return to the current gear. If the system is operating normally, then proceed to Displaying Codes.
If the TCCM failed the Self-Test, then test the following circuits.
• Battery Positive Voltage (40 and 1640), and Ignition 3 Voltage for battery voltage
• Ground Circuit for ground
• Diagnostic enable circuit for an open or high resistance
• Transfer case shift control switch connector
If the above circuits are normal but the TCCM still fails the Self-Test, replace the TCCM. Refer to Transfer Case Shift Control Module Replacement .

DTC Displaying
Turn OFF the ignition for 10 seconds.
Connect PIN 13 on the data link cable (DLC) to a ground. The DLC is located in the cab under the instrument panel on the driver's side.
Turn ON the ignition, with the engine OFF.
Observe the transfer case shift control switch select buttons for flashing codes. Refer to Diagnostic Trouble Code (DTC) List .
Important: If the transfer case shift control switch buttons all blink only once and then stop, no fault codes are stored in the transfer case shift control module.
• When one DTC is stored in memory, that code will blink that number of times followed by a 3 second pause and then repeat.
• If more than one code is stored, the first code will blink, followed by a 3 second pause and then the second code will blink.
• This sequence will continue until PIN 13 on the DLC is no longer grounded.
• If the TCCM will not communicate the presence or absence of DTCs, test the above circuits in Self-Test Step 2. If the circuits are complete, then replace the TCCM. Refer to Transfer Case Shift Control Module Replacement .

The four button switch system is a bit more complex ,need a factory scanner or professional one to check DTC'S

DTC B2725
DTC C0300
DTC C0305
DTC C0308
DTC C0309
DTC C0310
DTC C0315
DTC C0323
DTC C0324
DTC C0327
DTC C0362
DTC C0367
DTC C0374
DTC C0376
DTC C0387
DTC C0550
DTC C0611
this is where you should start ,checking code's .

Hi Jimi , There are very specific diagnostic procedures to follow for diagnosing this system. First a good visual inspection of the transfer case an fluid level an wiring connections. The transfer case shift control module is equipped with the ability to store diagnostic information, which is useful to a technician in the event of module, component or wiring failures. This information can be retrieved from the transfer case shift control module by way of flash codes, which are displayed on the three transfer case shift control switch buttons. These buttons are located on the instrument panel to the right of the steering wheel Before obtaining DTCs, perform the following transfer case control module (TCCM) Self-Test.
TCCM Self-Test

1. Observe the transfer case shift control switch indicators while turning the ignition switch to RUN. A properly operating system will flash all indicators and then will return to the current gear. If the system is operating normally, then proceed to Displaying Codes.
2. If the TCCM failed the Self-Test, then test the following circuits.
?€¢
Battery Positive Voltage (40 and 1640), and Ignition 3 Voltage for battery voltage



?€¢
Ground Circuit for ground



?€¢
Diagnostic enable circuit for an open or high resistance



?€¢
Transfer case shift control switch connector


3. If the above circuits are normal but the TCCM still fails the Self-Test, replace the TCCM. Refer to Transfer Case Shift Control Module Replacement .

DTC Displaying

1. Turn OFF the ignition for 10 seconds.
2. Connect PIN 13 on the data link cable (DLC) to a ground. The DLC is located in the cab under the instrument panel on the driver's side.
3. Turn ON the ignition, with the engine OFF.
4. Observe the transfer case shift control switch select buttons for flashing codes. Refer to Diagnostic Trouble Code (DTC) List .

Important: If the transfer case shift control switch buttons all blink only once and then stop, no fault codes are stored in the transfer case shift control module.
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When one DTC is stored in memory, that code will blink that number of times followed by a 3 second pause and then repeat.

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If more than one code is stored, the first code will blink, followed by a 3 second pause and then the second code will blink.

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This sequence will continue until PIN 13 on the DLC is no longer grounded.

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If the TCCM will not communicate the presence or absence of DTCs, test the above circuits in Self-Test Step 2. If the circuits are complete, then replace the TCCM. Refer to Transfer Case Shift Control Module Replacement .

Let me know if you have any codes , I have code definitions an procedures.

Which 4X4 system does your tahoe have ?
Transfer Case System Description (Selectable 4WD)
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.

Transfer Case System Description (Automatic 4WD)
The two speed Auto transfer case system utilizes a part time front axle. The system allows the driver to select the transfer case position with a touch of a button. The following positions can be selected: 4-wheel drive high range (4H), All Wheel Drive (AUTO), 2 Wheel Drive high range (2H), Neutral (N), and 4-Wheel Drive low range (4L).
The Auto Transfer Case (ATC) Control Module controls all the shifting action of the transfer case based on input from the driver as well as information from the Vehicle Control Module (VCM) /Powertrain Control Module (PCM).
4WD (4H or 4L) mode: This is accomplished by engaging the front axle, applying PWM to an electric motor to apply maximum torque, (fully compressing the transfer case clutch plates) to the front axle, then removing the ground on circuit 1569, thus locking the motor in position and stop the PWM to the motor.
AUTO mode: When in this mode of operation, the system should engage the front axle, then it monitors the front and rear propshaft speeds for any speed differences. When the system senses rear wheel slip, a difference of propshaft speed between front and rear, the Auto Transfer Case (ATC) Control Module will use pulse width modulation (PWM) to drive an electric motor. This motor transfers only the required torque to the front wheels to gain additional traction on slippery surfaces up to 75 mph. There is no torque applied to the front wheels until the module senses rear wheel slip.
Throttle anticipation (only operational when in AUTO mode): If the vehicle is below 5 mph and the accelerator is pressed quickly beyond a set point, the system will automatically transfer a percentage of torque to the front wheels to help prevent the rear wheels from slipping, as in a hard acceleration from a stopped position.
The Auto Transfer Case (ATC) Control Module also has the capability of engaging the front axle while the vehicle is in motion. It does this by applying PWM to the electric motor to apply torque to the front axle, this action is used to match the speed of the front and rear propshafts. After the module senses the proper speed, it then supplies a ground on circuit 1570 to engage the front axle.
The Auto Transfer Case (ATC) Control Module will accept a mode shift only when the engine is running and a valid Motor/Encoder signal is present. A mode shift is any shift between 2H, 4H, and AUTO.
The Auto Transfer Case (ATC) Control Module will permit a range shift only if the following conditions are met within 30 seconds of the request:

Automatic 4WD Diagnostic Aids
A Scan Tool reads and displays the following information:
• Diagnostic Trouble code(s)
• Code status bit (are codes set or not)
• Transfer case lock status
• Lamp in the switch/lamp assembly
• Motor/Encoder gear position
• Ignition (3) voltage
• Front propshaft speed sensor (KPH)
• Front axle switch (open/closed)
• Front axle requested position (engaged/disengaged)
• Rear propshaft speed sensor (KPH)
• Mode switch position request
• Park switch (open/closed)
• 4WD (Adapt) Mode Auto bit
• Current Mode corrective action PWM
• Average and highest PWM applied during last slip recovery event
• Throttle anticipation mode
• Average and highest PWM applied during last Throttle anticipation corrective action event
• Difference between front and rear propshaft RPM
• Adapt event counter
• Throttle position sensor percentage

Check the transfer case shift control module for DTC's. The transfer case shift control module is not a class 2 device. DTC's are displayed on the transfer case shift control switch. Refer to Diagnostic Trouble Code (DTC) Displaying .
Are any DTC's present?
Diagnostic Trouble Code (DTC) Displaying
The transfer case shift control module is equipped with the ability to store diagnostic information, which is useful to a technician in the event of module, component or wiring failures. This information can be retrieved from the transfer case shift control module by way of flash codes, which are displayed on the three transfer case shift control switch buttons. These buttons are located on the instrument panel to the right of the steering wheel Before obtaining DTCs, perform the following transfer case control module (TCCM) Self-Test.
TCCM Self-Test
Observe the transfer case shift control switch indicators while turning the ignition switch to RUN. A properly operating system will flash all indicators and then will return to the current gear. If the system is operating normally, then proceed to Displaying Codes.
If the TCCM failed the Self-Test, then test the following circuits.
• Battery Positive Voltage (40 and 1640), and Ignition 3 Voltage for battery voltage
• Ground Circuit for ground
• Diagnostic enable circuit for an open or high resistance
• Transfer case shift control switch connector
If the above circuits are normal but the TCCM still fails the Self-Test, replace the TCCM. Refer to Transfer Case Shift Control Module Replacement .
DTC Displaying
Turn OFF the ignition for 10 seconds.
Connect PIN 13 on the data link cable (DLC) to a ground. The DLC is located in the cab under the instrument panel on the driver's side.
Turn ON the ignition, with the engine OFF.
Observe the transfer case shift control switch select buttons for flashing codes. Refer to Diagnostic Trouble Code (DTC) List .
Important: If the transfer case shift control switch buttons all blink only once and then stop, no fault codes are stored in the transfer case shift control module.
• When one DTC is stored in memory, that code will blink that number of times followed by a 3 second pause and then repeat.
• If more than one code is stored, the first code will blink, followed by a 3 second pause and then the second code will blink.
• This sequence will continue until PIN 13 on the DLC is no longer grounded.
• If the TCCM will not communicate the presence or absence of DTCs, test the above circuits in Self-Test Step 2. If the circuits are complete, then replace the TCCM. Refer to Transfer Case Shift Control Module Replacement .

More then likely the problem is in the motor of the transfer case controller

co327 is a code for your transfer case encoder motor and the U codes are communication codes. Most likely cause is the encoder motor needs replacement

The New Venture Gear Model NV233 is an electronically controlled optional transfer case for use on four wheel drive T 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 4LO 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.

Transfer Case Control Module Description
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
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
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.
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.

Before replacing parts you should test the system !
Diagnostic Trouble Code (DTC) Displaying
The transfer case shift control module is equipped with the ability to store diagnostic information, which is useful to a technician in the event of module, component or wiring failures. This information can be retrieved from the transfer case shift control module by way of flash codes, which are displayed on the three transfer case shift control switch buttons. These buttons are located on the instrument panel to the right of the steering wheel Before obtaining DTCs, perform the following transfer case control module (TCCM) Self-Test.
TCCM Self-Test
Observe the transfer case shift control switch indicators while turning the ignition switch to RUN. A properly operating system will flash all indicators and then will return to the current gear. If the system is operating normally, then proceed to Displaying Codes.
If the TCCM failed the Self-Test, then test the following circuits.
• Battery Positive Voltage (40 and 1640), and Ignition 3 Voltage for battery voltage
• Ground Circuit for ground
• Diagnostic enable circuit for an open or high resistance
• Transfer case shift control switch connector
If the above circuits are normal but the TCCM still fails the Self-Test, replace the TCCM. Refer to Transfer Case Shift Control Module Replacement .
DTC Displaying
Turn OFF the ignition for 10 seconds.
Connect PIN 13 on the data link cable (DLC) to a ground. The DLC is located in the cab under the instrument panel on the driver's side.
Turn ON the ignition, with the engine OFF.
Observe the transfer case shift control switch select buttons for flashing codes. Refer to Diagnostic Trouble Code (DTC) List .
Important: If the transfer case shift control switch buttons all blink only once and then stop, no fault codes are stored in the transfer case shift control module.
• When one DTC is stored in memory, that code will blink that number of times followed by a 3 second pause and then repeat.
• If more than one code is stored, the first code will blink, followed by a 3 second pause and then the second code will blink.
• This sequence will continue until PIN 13 on the DLC is no longer grounded.
• If the TCCM will not communicate the presence or absence of DTCs, test the above circuits in Self-Test Step 2. If the circuits are complete, then replace the TCCM. Refer to Transfer Case Shift Control Module Replacement .

Is the 4WD fuse # 15 -10 amp located in the I/P fuse box good ?

It means your 4 wheel drive system needs to be serviced or is detecting a malfunction.

As long as the transfer-case is a New Process Gear 233C Pro code NP1 which was used from 1995 to 2005 on the Blazers. Keep in mind also there there was the NP233C Pro code NP6 which was used in the years 1998 to 2005 and NP8 which was used from 199 to 2003 so your going to need to know which PRO code transfer case you have in your Blazer. You can look that up on your PRO sticker in your glove box and look for NP1 or NP6 which would indicate which transfer-case you have.

Thank you for using fixya and good luck.