Now to get in the diagnostic mode

Hooking up a factory or someother type professional scan tool an checking for DTC'S - diagnostic trouble codes stored in the 4X4 control module is the proper way to start diagnostics . Your best bet ,have a qualified repair shop check it out .

Principles of Operation
The electronic shift on the fly (ESOF) system is an electronic shift system that allows the operator to choose between 2 different 4-wheel drive modes as well as 2-wheel drive. The operator can switch between 2WD and 4H mode at speeds up to 88 km/h (55 mph). To engage or disengage 4L range, the vehicle speed must be less than 5 km/h (3 mph), the brake pedal pressed and the transmission must be in NEUTRAL (or the clutch pedal pressed in manual transmission vehicles).
When the mode select switch (MSS) on the instrument panel is turned, the 4WD control module (PCM) activates the electromagnetic clutch and powers the transfer case shift motor. When the shift motor reaches the desired position, as determined by the contact plate position inputs to the 4WD control module (PCM), power to the shift motor will be removed. When the transfer case front and rear output shafts are synchronized, the spring loaded lockup collar mechanically engages the mainshaft hub to the drive sprocket. Finally, the front axle integrated wheel ends (IWEs) are engaged and the electromagnetic clutch is deactivated.

Feature Inputs:
• Mode select switch (MSS)
• Wheel speeds (via CAN communication)
• Contact plate position inputs A, B, C, D (grounded when closed, open circuit when open)
• Transmission neutral
• Brake ON/OFF (BOO)

Feature Outputs:
• Transfer case synchronization clutch
• Transfer case shift motor relays
• Integrated wheel-end (IWE) vacuum solenoid
• Instrument cluster indicators (via CAN communication)
• 4WD mode (via CAN communication to PCM)
• Inspection and Verification
  
  1. Verify the customer concern.
  1. Visually inspect for obvious signs of mechanical or electrical damage.
  
  
  Visual Inspection Chart Mechanical Electrical
  • Halfshafts
  • Integrated wheel ends (IWE)
  • Shift motor
  • Driveshaft and universal joints
  • Vacuum leaks
  • Fluid leaks
  • Matching tire sizes
  • Transfer case
  • Central junction box (CJB) mini fuses:
    • 11 (10A) (IWE vacuum solenoid)
    • 28 (5A)
    • 29 (15A)
    • 30 (15A)
  • CJB fuse 111 (20A)
  • Wiring harness
  • Mode select switch (MSS)
  • Synchronization clutch
  • Connector(s)
  • IWE vacuum solenoid
  • Circuitry
  
  
  1. If an obvious cause for an observed or reported concern is found, correct the cause (if possible) before proceeding to the next step.
  1. If the cause is not visually evident, connect the diagnostic tool to the data link connector and select the vehicle to be tested from the diagnostic tool menu. If the diagnostic tool does not communicate with the vehicle:
  • check that the program card is correctly installed (if using NGS+).
  • check the connections to the vehicle.
  • check the ignition switch position.
  1. If the diagnostic tool still does not communicate with the vehicle, refer to the diagnostic tool operating manual.
  1. Carry out the data link diagnostics test. If the diagnostic tool responds with:
  • SCP+, SCP-, UBP, CAN or ISO circuits fault; all electronic control units no response/not equipped, refer to Section 418-00 .
  • No response/not equipped for powertrain control module (PCM). Refer to Section 418-00 to diagnose module communication problems.
  • No response/not equipped for 4WD control module (PCM), Go To Pinpoint Test J .
  • System passed, retrieve and record the continuous diagnostic trouble codes (DTCs), erase the continuous DTCs and carry out the self-test diagnostics for the 4WD control module (PCM).
  1. If the DTCs retrieved are related to the concern, go to the 4WD Control Module (PCM) DTC Index to continue diagnostics.
  1. If no DTCs related to the concern are retrieved, GO to Symptom Chart .
  2. 4WD Control Module (PCM) Diagnostic Trouble Code (DTC) Index
     DTC Description Source Action B1317 Battery Voltage High 4WD Control Module (PCM) CHECK the battery and charging system for faults. REFER to Section 414-00 . CLEAR the DTC. REPEAT the self-test. B1318 Battery Voltage Low 4WD Control Module CHECK the battery and charging system for faults. REFER to Section 414-00 . CLEAR the DTC. REPEAT the self-test. B1342 ECU is Defective 4WD Control Module CLEAR the DTC. REPEAT the self-test. If DTC B1342 is retrieved, INSTALL a 4WD control module (integral to the PCM). REFER to Section 303-14 . REPEAT the self-test. C1728 Transfer Case Unable to Transition Between 2WD HIGH and 4WD HIGH 4WD Control Module Go To Pinpoint Test L . C1729 Transfer Case Unable to Transition Between 4WD HIGH and 4WD LOW 4WD Control Module Go To Pinpoint Test M . C1979 IWE Solenoid Circuit Failure 4WD Control Module Go To Pinpoint Test K . C1980 IWE Solenoid Circuit Short to Battery 4WD Control Module Go To Pinpoint Test K . P1812 Transmission 4-Wheel Drive Mode Select Circuit Failure 4WD Control Module Go To Pinpoint Test L . P1815 Transmission 4-Wheel Drive Mode Select Short Circuit to Ground 4WD Control Module Go To Pinpoint Test L . P1820 Transfer Case Clockwise Shift Relay Coil Circuit Failure 4WD Control Module Go To Pinpoint Test L . P1822 Transfer Case Clockwise Shift Relay Coil Short Circuit To Battery 4WD Control Module Go To Pinpoint Test L . P1824 Transmission 4-Wheel Drive Clutch Relay Circuit Failure 4WD Control Module Go To Pinpoint Test N . P1826 Transmission 4-Wheel Drive Low Clutch Relay Short Circuit to Battery 4WD Control Module Go To Pinpoint Test N . P1827 Transmission 4-Wheel Drive Low Clutch Relay Short Circuit to Ground 4WD Control Module Go To Pinpoint Test N . P1828 Transfer Case Counterclockwise Shift Relay Coil Circuit Failure 4WD Control Module Go To Pinpoint Test L . P1830 Transfer Case Counterclockwise Shift Relay Coil Short Circuit To Battery 4WD Control Module Go To Pinpoint Test L . P1849 Transmission Transfer Case Contact Plate A Short Circuit to Ground 4WD Control Module Go To Pinpoint Test L . P1853 Transmission Transfer Case Contact Plate B Short Circuit to Ground 4WD Control Module Go To Pinpoint Test L . P1857 Transmission Transfer Case Contact Plate C Short Circuit to Ground 4WD Control Module Go To Pinpoint Test L . P1861 Transmission Transfer Case Contact Plate D Short Circuit to Ground 4WD Control Module Go To Pinpoint Test L . P1867 Transmission Transfer Case Contact Plate General Circuit Failure 4WD Control Module Go To Pinpoint Test L . P1891 Transmission Transfer Case Contact Plate Ground Return Open Circuit 4WD Control Module Go To Pinpoint Test L . U1900 CAN Communication BUS Fault - Received Error 4WD Control Module DIAGNOSE the module communication network. REFER to Section 418-00 . U2023 Fault Received From External Node 4WD Control Module DIAGNOSE the module communication network. REFER to Section 418-00 . U2051 One Or More Calibration Files Missing/Corrupt 4WD Control Module Method 3 programming fault. REFER to Section 418-00 for 4WD control module (PCM) programming information.

Without hooking up a factory or professional scan tool an checking for DTC'S - diagnostic trouble code's . And or going through other diagnostic procedures for Transfer Case Shift Control Switch Indicator Flashes, then Returns to Previous Mode an other diagnostic testing procedures ,you should not replace anything . You best bet ,take it to a qualified repair shop. Do you know what DTC'S are ? What an electronic control module is ?
The transfer case brake control is supplied voltage at all times, with the key ON, through the B+ circuit. The brake control is activated when the transfer case shift control module registers the following modes:
• AUTO FWD
• 4HI
• 4LO
This is accomplished when the transfer case shift control module provides ground to the brake control through the T-Case Lock circuit. If there is a fault in the brake control circuit, the transfer case shift control module goes into a shift block mode. The shift block mode causes the mode indicator to flash for 10 seconds when another mode is selected. After the 10 second period has ended, the indicator reverts back to the previous mode selection.

DTC B0770
DTC B0775
DTC B0780
DTC B0785
DTC B0790
DTC B2725
DTC C0300
DTC C0305
DTC C0306
DTC C0321
DTC C0327
DTC C0359
DTC C0374
DTC C0379
DTC C0550

Without proper diagnostic tool's an factory service repair information an knowledge how it work's , very doubtful you could fix these , or should you try .

When you change the mode from floor to vent to defrost do you hear switching taking place behind the dash or inside ?

Air Delivery Improper

Test Description
The numbers below refer to the step numbers on the diagnostic table.
The measured voltage should be near the specified values for each mode position.
The HVAC control module is supplied by two ignition 3 voltage circuits. Test the ignition 3 voltage circuit that does not supply the blower motor switch.
Step
Action
Value
Yes
No
Schematic Reference: HVAC Schematics
Connector End View Reference: HVAC Connector End Views
DEFINITION: Air does not flow correctly from the air distribution outlets.
1
Did you perform the HVAC Diagnostic System Check?
--
YES - Go to Step 2
NO - Go to Diagnostic System Check - HVAC Systems - Manual
2
Turn ON the ignition, with the engine OFF.
Place the blower motor switch in the OFF position.
Is the blower motor OFF?
--
YES - Go to Step 3
NO - Go to Blower Motor Always On
3
Place the blower motor switch in each speed position.
Does the blower motor operate at all?
--
YES - Go to Step 4
NO - Go to Blower Motor Inoperative
4
Does the blower motor operate in each speed position?

YES - Go to Step 5
NO - Go to Blower Motor Malfunction
5
Except for the blower motor speed, are all of the functions of the HVAC control module inoperative?
--
YES - Go to Step 14
NO - Go to Step 6
6
Place the blower motor switch in the maximum speed position.
Place the mode switch in the vent position.
Place the recirculation switches in the recirculation position and in the outside air position.
Does the recirculation door move to the correct position for each selection?
--
YES - Go to Step 7
NO - Go to Air Recirculation Malfunction
7
Place the blower motor switch in the maximum speed position.
Place the mode switch in each position.
Is the air flow sufficient from the correct outlets in each mode?
--
YES - Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems
NO - Go to Step 8
8
Inspect the air distribution system for the following conditions:
• A dirty HVAC air filter, if applicable
• An obstruction to the air flow
• Air leaks
• Misaligned air ducts
Did you find and correct the condition?
--
YES - Go to Step 23
NO - Go to Step 9
9
Inspect the mode door and the mode actuator for the following conditions:
• A misaligned mode actuator
Refer to Mode Actuator Replacement .
• Broken or binding linkages or mode door
• An obstruction that prevents the mode actuator from operating within its full range of motion
• Missing seals to the mode door
• Misaligned seals to the mode door
Did you find and correct the condition?
--
YES - Go to Step 23
NO - Go to Step 10
10
Turn OFF the ignition.
Disconnect the mode actuator.
Turn ON the ignition, with the engine OFF.
Probe the ignition 3 voltage circuit of the mode actuator with a test lamp that is connected to a good ground.
Does the test lamp illuminate?
--
YES - Go to Step 11
NO - Go to Step 20
11
Test the ground circuit of the mode actuator for an open or high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?
--
YES - Go to Step 23
NO - Go to Step 12
12
Measure the voltage from the mode door control circuit of the mode actuator to a good ground.
Place the mode switch in each mode position while observing the voltage.
Does the voltage measure near the specified values for each mode position?
Vent 0.2V, Bi-Level 3.0V, Floor 6.0V, Mix-Blend 9.0V, Defrost 12.0V
YES - Go to Step 18
NO - Go to Step 13
13
Test the mode door control circuit of the mode actuator for an open, high resistance, short to ground, or short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?
--
YES - Go to Step 23
NO - Go to Step 19
14
Test the ignition 3 voltage circuit of the HVAC control module for an open or high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?
--
YES - Go to Step 23
NO - Go to Step 15
15
Test the battery positive voltage circuit of the HVAC control module for an open or high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?
--
YES - Go to Step 23
NO - Go to Step 16
16
Test the ground circuit of the HVAC control module for an open or high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?
--
YES - Go to Step 23
NO - Go to Step 17
17
Test the off blower motor control circuit of the HVAC control module for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?
--
YES - Go to Step 23
NO - Go to Step 19
18
Inspect for poor connections at the harness connector of the mode actuator. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.
Did you find and correct the condition?
--
Go to Step 23
Go to Step 21
19
Inspect for poor connections at the harness connector of the HVAC control module. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.
Did you find and correct the condition?
--
Go to Step 23
Go to Step 22
20
Repair the ignition 3 voltage circuit of the mode actuator. Refer to Wiring Repairs in Wiring Systems.
Did you complete the repair?
--
Go to Step 23
--
21
Replace the mode actuator. Refer to Mode Actuator Replacement .
Did you complete the replacement?
--
Go to Step 23
--
22
Replace the HVAC Control module. Refer to HVAC Control Module Replacement .
Did you complete the replacement?
--
Go to Step 23
--
23
Operate the system in order to verify the repair.
Did you correct the condition?
--
System OK
Go to Step 8

Air Distribution
The HVAC control module controls the distribution of air by the use of a defrost actuator and a mode actuator. The modes that may be selected are:
?€¢
Defrost

?€¢
Defog

?€¢
Panel

?€¢
Bi-Level

?€¢
Floor

The mode and defrost actuators are connected to the mode and defrost doors by a cam type linkage system. Depending on the position of the door, air is directed through the HVAC module and distributed through various ducts leading to the outlets in the dash. If the HVAC control module detects a fault with the mode or defrost doors the HVAC control module will try to drive the actuator for a predetermined amount of time, to defrost, which is the defaulted position for the mode and defrost door actuators. When the mode switch is placed in the defrost or defog positions the A/C is commanded on and the recirculation door is moved to the outside air position to help reduce window fogging. A/C is available in all modes and recirculation is only available in the panel and bi-level modes.
Circuit Description The following DTCs are for the HVAC door actuators: ?€¢
B0248 is for the defrost actuator.
?€¢
B0263 is for the mode actuator.
?€¢
B0408 is for the left air temperature actuator.
?€¢
B0418 is for the right air temperature actuator.
The HVAC control module controls the HVAC door actuators to regulate the airflow through the HVAC system. Each actuator consists of a stepper motor, a logic circuit, and a potentiometer. The potentiometer inside the door actuator allows the module to monitor the current position of the actuator drive shaft. The logic circuit inside the actuators receives control signals from the HVAC control module and controls the internal stepper motor. When a door positional change is required, the HVAC control module calculates a commanded door position. The module compares the commanded door position to the actual door position and determines the needed direction of motor rotation. The module applies a signal voltage to the door control circuit that is an input to the internal logic circuit of the door actuator. A 5 volt signal increases the door position. A 0 volt signal decreases the door position. When the commanded door position is equal to the actual door position, the HVAC control module sends a 2.5 volt signal to the door actuator and motor rotation stops. The ignition 3 voltage circuit provides source voltage to the logic circuit. The module provides ground to the actuator logic circuit through the low reference circuit. I would start by having the HVAC control module checked for DTC'S -diagnostic trouble codes First . Then check the system by using scan tool data . 1
Did you perform the HVAC Diagnostic System Check?
Go to Step 2
Go to Diagnostic System Check - HVAC Systems - Manual

2

1. Install a scan tool.
2. Turn ON the ignition, with the engine OFF.
3. With a scan tool, command the appropriate HVAC door actuator ON and OFF while observing the corresponding Door Actual parameter.

Does the scan tool indicate that the value of the appropriate Door Actual parameter changes?
Go to Diagnostic Aids
Go to Step 3

I would

code p 1402 refers to fuel tank leakage diagnostic module--motor malfunction===causes --fuel tank leakage motor diagnostic module motor
code p 1403 refers to the fuel tank diagnostic module ---valve malfunction
go to a service dealer and have the unit tested
it is possible that by replacing or cleaning the valve section , the problem will be fixed

The rear wiper / washers are controlled by the GEM - generic electronic module .
NOTE: The generic electronic module (GEM) will not activate the rear wiper system if either the liftgate or the liftgate glass is ajar. If either the liftgate or the liftgate glass becomes ajar while the rear wiper is in operation, the GEM will park the rear wiper motor.
There are two distinct modes of wiper operation:

• Off Mode: In this mode, there is no rear wiper activity, and the wiper motor will be in the PARK position.
• Interval Mode: This mode is selected when the rear wiper switch is in either the Interval 1 or 2 position. When this mode is selected, the rear wiper motor is driven up onto the glass by activating the rear wiper UP relay. When the wiper motor HIGH/LOW/PARK position input reaches the high position, the UP relay is deactivated and the DOWN relay is activated to reverse the wiper motor direction. When the wiper motor reaches the LOW position, as determined by the HIGH/LOW/PARK position input, the GEM deactivates the DOWN relay and will begin a new wiper cycle 1 to 10 seconds later, depending on the interval position selected.

Inspection and Verification

1. The wiper/washer system is a generic electronic module (GEM) controlled system; refer to Section 419-10 .

1. Verify the customer concern by operating the wiper/washer system.

1. Visually inspect for obvious signs of mechanical and electrical damage.

Visual Inspection Chart Mechanical Electrical

• Hoses to windshield washer pump
• Wiper linkage

• Fuses 6 (5A), 8 (5A), 15 (5A), and 20 (5A)
• Wiring harness
• Loose or corroded connector(s)
• Relays
• Motors
• Multifunction switch
• Washer fluid level switch

1. If the concern remains after the inspection, connect New Generation STAR (NGS) Tester to the data link connector (DLC) located beneath the instrument panel and select the vehicle to be tested from the NGS menu. If NGS Tester does not communicate with the vehicle:
   • Check that the program card is properly installed.
   • Check the connections to the vehicle.
   • Check the ignition switch position.

1. If NGS Tester still does not communicate with the vehicle, refer to the New Generation STAR Tester manual.

1. Perform the DATA LINK DIAGNOSTIC TEST. If NGS Tester responds with:
   • CKT914, CKT915 or CKT70 = ALL ECUS NO RESP/NOT EQUIP, refer to Section 418-00 .
   • NO RESPONSE/NOT EQUIPPED for generic electronic module (GEM), go to Pinpoint Test M.
   • SYSTEM PASSED, retrieve and record the continuous diagnostic trouble codes (DTCs), erase the continuous DTCs and perform self-test diagnostics for the GEM.

1. If the DTCs retrieved are related to the concern, go to GEM Diagnostic Trouble Code (DTC) Index to continue diagnostics.

1. If no DTCs related to the concern are retrieved, proceed to Symptom Chart to continue diagnostics. Your best bet is take this to a ASE certified repair shop !

All fuses supply power to the four wheel drive control module , the control module supplies power to mode select switch . The 4WD control module accomplishes shifts by interpreting inputs from the following:

• mode select switch (MSS)
• vehicle speed signal
• encoder plate position
• brake pedal switch
• digital transmission range (TR) sensor
• ignition switch
• transfer case shift motor
• Based on these inputs, the 4WD control module controls the shifts into 2WD, 4WD HIGH or 4WD LOW with the following outputs:
  
  • shift motor (clockwise)
  • shift motor (counterclockwise)
• Fuses
• Battery junction box (BJB) fuse:
  • 1 (50A)
  • 3 (50A)
  • 13 (20A)
  • 30 (10A)
• Central junction box (CJB) fuse:
• 28 (7.5A) (manual transmission)
• 10 (7.5A)
• 11 (7.5A)
• 5 (15A)
• If the concern remains after the inspection, connect the diagnostic tool to the data link connector (DLC) located beneath the instrument panel and select the vehicle to be tested from the diagnostic tool menu.

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 .

That is fault code 136
136. (10001000) Motor Stall
The Motor Control Module has been unable to start the motor. Possible causes of this fault
are: Faulty motor harness, faulty or jammed motor, seized bearings or seals, faulty Motor
Control Module, faulty Rotor Position Sensor or harness.
Primary Source: Wiring.
Action: Measure/check the motor harness, connectors and motor for
discontinuity. This can be done by taking a resistance measurement
between phases of the motor harness at the Motor Control Module
end. Nominal resistance should be around 32 Ohms.
Secondary Source: Motor.
Action: 1) Check free rotation of the agitator and basket by rotating by hand.
Bearings and seals may be seized.
2) Check the Rotor Position Sensor and associated harness for
water, mechanical damage or corrosion.
Tertiary Source: Motor Control Module.
Action: If the primary and secondary checks pass inspection, then replace
the Motor Control Module.

2-Speed Torque-On-Demand (TOD) Operation
The automatic 4-wheel drive (A4WD) system is a 2-speed torque-on-demand (TOD) operation that utilizes the following components:

• Transfer case
• 4-wheel drive (4WD) control module (integral to the powertrain control module [PCM])
• Mode select switch (MSS)
• Gearmotor encoder assembly (part of the transfer case shift motor)
• Transfer case shift motor
• Shift motor sense plate (part of the gearmotor encoder assembly)

Principles of Operation
Transfer Case Shift Motor The externally mounted transfer case shift motor, located at the rear of the transfer case, turns the shift cam assembly. As the shift cam assembly turns, it positions the reduction shift fork for desired transfer case operation. An integral position sensor in the shift motor provides shift motor position information to the 4WD control module.
Mode Select Switch (MSS) The push button MSS, mounted on the instrument panel, allows the operator to select the 4x4 Auto, 4x4 High, and 4x4 Low transfer case operating modes. The indicator light, on the instrument cluster push button, will illuminate only when the 4x4 Low position is engaged.
Visual Inspection Chart Mechanical Electrical

• Axle shafts and CV joints
• Driveshaft and universal joints
• Fluid leaks
• Matching tire sizes
• Transfer case shift motor

• Battery junction box (BJB) fuses:
  • 8 (30A)
  • 17 (5A)
  • 18 (20A)
• Central junction box (CJB) fuses:
  • 12 (5A)
  • 24 (15A)
• 4x4 module (PCM)
• Wiring harness
• Gearmotor encoder contact plate
• Connector(s)
• Circuitry
• Mode indication switch (MSS)

1. If an obvious cause for an observed or reported concern is found, correct the cause (if possible) before proceeding to the next step.

1. If the concern is not visually evident, connect the diagnostic tool to the data link connector and select the vehicle to be tested from the diagnostic tool menu. If the diagnostic tool does not communicate with the vehicle:
   • check that the program card is correctly installed.
   • check the connections to the vehicle.
   • check the ignition switch position.

1. If the diagnostic tool still does not communicate with the vehicle, refer to the diagnostic tool operating manual.

1. Carry out the diagnostic tool data link test. If the diagnostic tool responds with:
   • CAN circuit fault; all electronic control units no response/not equipped, refer to Section 418-00 .
   • No response/not equipped for 4WD module (PCM), Go To Pinpoint Test G .
   • System passed, retrieve and record the continuous diagnostic trouble codes (DTCs), erase the continuous DTCs and carry out the 4WD module (PCM) self test.

1. If the DTCs retrieved are related to the concern, go to the 4WD Control Module (PCM) Diagnostic Trouble Code (DTC) Index to continue diagnostics. 4WD Control Module (PCM) Diagnostic Trouble Code (DTC) Index
   DTC Description Source Action B1317 Battery Voltage HIGH 4WD Module (PCM) REFER to Section 414-00 . B1318 Battery Voltage LOW 4WD Module (PCM) REFER to Section 414-00 . B1319 Driver Door Ajar Circuit Failure 4WD Module (PCM) Go To Pinpoint Test M . B1322 Driver Door Ajar Circuit Short To Ground 4WD Module (PCM) Go To Pinpoint Test M . B1342 ECU is Defective 4WD Module (PCM) CLEAR the DTCs. REPEAT the 4x4 module (PCM) self test. If DTC B1342 is retrieved, INSTALL a new 4x4 module (PCM). REFER to Section 303-14 . CLEAR the DTCs. REPEAT the self test. B1483 Brake Pedal Input Circuit Failure 4WD Module (PCM) Go To Pinpoint Test M . B1485 Brake Pedal Input Short to Battery 4WD Module (PCM) Go To Pinpoint Test M . C1729 Transfer Case Unable to Transition Between 4H and 4L 4WD Module (PCM) Go To Pinpoint Test K . C1970 4WD Low Mode Switch LED Short to Battery 4WD Module (PCM) Go To Pinpoint Test K . C1971 4WD Low Mode Switch LED Circuit Failure 4WD Module (PCM) Go To Pinpoint Test K . P1707 Transfer Case NEUTRAL or PARK/NEUTRAL Indication Circuit 4WD Module (PCM) Go To Pinpoint Test M . P1812 Transmission 4-Wheel Drive Mode Select Circuit Failure 4WD Module (PCM) Go To Pinpoint Test K . P1815 Transmission 4-Wheel Drive Mode Select Short Circuit to Ground 4WD Module (PCM) Go To Pinpoint Test K . P1816 Transmission NEUTRAL Safety Switch Circuit Failure 4WD Module (PCM) Go To Pinpoint Test M . P1819 Transmission NEUTRAL Safety Switch Circuit Short to Ground 4WD Module (PCM) Go To Pinpoint Test M . P1820 Transfer Case Clockwise Shift Relay Coil Circuit Failure 4WD Module (PCM) Go To Pinpoint Test K . P1822 Transfer Case Clockwise Shift Relay Coil Circuit Short To Battery 4WD Module (PCM) Go To Pinpoint Test K . P1824 4-Wheel Drive Clutch Relay Circuit Failure 4WD Module (PCM) Go To Pinpoint Test H . P1826 4-Wheel Drive Low Clutch Relay Short Circuit to Battery 4WD Module (PCM) Go To Pinpoint Test H . P1827 4-Wheel Drive Low Clutch Relay Short Circuit to Ground 4WD Module (PCM) Go To Pinpoint Test H . P1828 Transfer Case Counterclockwise Shift Relay Coil Circuit Failure 4WD Module (PCM) Go To Pinpoint Test K . P1830 Transfer Case Counterclockwise Shift Relay Coil Circuit Short To Battery 4WD Module (PCM) Go To Pinpoint Test K . P1849 Transfer Case Contact Plate A Short Circuit to Ground 4WD Module (PCM) Go To Pinpoint Test K . P1853 Transfer Case Contact Plate B Short Circuit to Ground 4WD Module (PCM) Go To Pinpoint Test K . P1857 Transfer Case Contact Plate C Short Circuit to Ground 4WD Module (PCM) Go To Pinpoint Test K . P1861 Transfer Case Contact Plate D Short Circuit to Ground 4WD Module (PCM) Go To Pinpoint Test K . P1867 Transfer Case Contact Plate General Circuit Failure 4WD Module (PCM) Go To Pinpoint Test K . P1891 Transfer Case Contact Plate Ground Return Open Circuit 4WD Module (PCM) Go To Pinpoint Test K . U1900 CAN Communication BUS Fault 4WD Module (PCM) REFER to Section 418-00 . U2023 External Node Fault 4WD Module (PCM) REFER to Section 418-00 . U2051 One Or More Calibration Files Missing/Corrupt 4WD Module (PCM) Reprogram/Reflash the 4x4 module. REFER to Section 418-00 . - For All Other DTCs 4WD Module (PCM) REFER to Section 418-00 .
2. Your best bet mite be to take it to a qualified repair shop !