2009 hummer H3.. I have a code co327 it says encoder circuit short to ground or open..and code co276 transmission control module communication problem.. any idea how to fix ?

Question edited for clarity.
don't is a contraction of 'do not', doesn't is a contraction of 'does not'. I changed it.

This seems to explain the issue. Or if nothing lights up, check the fuse box diagram

https://www.justanswer.com/gm/5quae-gm-hummer-h3-2006-hummer-h3-107330-miles-no-lights-4x4.html

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 proper test your guess is as good as mine , or any ones . Looking up diagnostic procedures in service repair manual an testing for that code is the way to find the problem .


Circuit/System Testing
Note: Use the schematic to identify the following:
• Control modules the vehicle is equipped with
• Control module locations on the low and high speed GMLAN serial data circuits
• The control modules B+, ignition, ground, communication enable and serial data circuit terminals
Determine the module that is not communicating. Refer to Control Module U Code List.
U0109 00
Lost Communication with Fuel Pump Control Module

Ignition OFF, disconnect the necessary harness connector of the module that is not communicating.
Test for less than 5 ? between each ground circuit terminal and ground.
? If greater than the specified range, test the ground circuit for an open/high resistance.
If equipped, verify that a test lamp illuminates between each B+ circuit terminal and ground.
? If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit fuse is open, test the control circuits of the control module for a short to ground. If the circuits test normal, replace the control module.
If equipped, ignition ON, verify that a test lamp illuminates between each ignition circuit terminal and ground.
? If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance. If the circuit fuse is open, test the control circuits of the control module for a short to ground. If the circuits test normal, replace the control module.
Note: Only the high speed GMLAN modules have a serial data communication enable circuit OR an accessory wakeup serial data circuit, and the BCM is the output for these circuits. Refer to the module schematics to identify which modules have these circuits.
If equipped, ignition ON, verify that a test lamp illuminates between the communication enable circuit terminal OR the accessory wakeup circuit terminal and ground.
? If the test lamp does not illuminate, test the circuit for an open/high resistance. If the circuits test normal, replace the BCM.
Ignition OFF for 60 seconds, test for less than 5 ? between the serial data circuit terminals and the DLC terminal listed below:
• Class 2 serial data circuit terminal 2
• Low speed GMLAN serial data terminal 1
• High speed GMLAN serial data terminal 6 or 14
? If greater than the specified range, test the serial data circuit for an open/high resistance between the non communicating control module and a module setting the DTC or a serial data splice pack.
If all circuits test normal, replace the control module that is not communicating.

No fuse , sensor make own voltage
The vehicle speed sensor (VSS) provides vehicle speed information to the powertrain control module (PCM) or transmission control module (TCM). The VSS is a permanent magnet (PM) generator. The PM generator produces a pulsing AC voltage as rotor teeth on the transmission output shaft pass through the sensor's magnetic field. The AC voltage level and the number of pulses increase as the speed of the vehicle increases. Output voltage varies with speed from a minimum of 0.5 volts at 100 RPM to more than 100 volts at 8,000 RPM. The PCM/TCM converts the pulsing voltage to vehicle speed. The PCM/TCM uses the vehicle speed signal to determine shift timing and TCC scheduling.
. What code # P0 what ? What speed sensor ? VSS - vehicle speed sensor , wheel speed sensor ? No diagnostic code tells you the sensor is mess up . Sensors circuit's can set a number code's lo voltage , high voltage , short to ground , open circuit . Your best bet ,take it to a qualified repair shop.

Power an ground check for the BCM . Traction control an StabiliTrak are controlled by the EBCM - electronic brake control module . What year is your H3

The transmission range (TR) switch is part of the park/neutral position (PNP) and backup lamp switch assembly, which is externally mounted on the transmission manual shaft. The TR switch contains four internal switches that indicate the transmission gear range selector lever position. The powertrain control module (PCM) or transmission control module (TCM) supplies ignition voltage to each switch circuit. As the gear range selector lever is moved, the state of each switch may change, causing the circuit to open or close. An open circuit or switch indicates a high voltage signal. A closed circuit or switch indicates a low voltage signal. The PCM/TCM detects the selected gear range by deciphering the combination of the voltage signals. The PCM/TCM compares the actual voltage combination of the switch signals to a TR switch combination chart stored in memory.

It's on the outside of the transmission ,

DTC U0100-U0299
Circuit/System Description
The serial data circuit is the means by which the control modules in the vehicle communicate with each other. Once the scan tool is connected to the serial data circuit through the DLC, the scan tool can be used to monitor each module for diagnostic purposes and to check for diagnostic trouble codes (DTCs). When the ignition switch is in RUN, each control module communicating on the serial data circuit sends a state of health (SOH) message to ensure that the control module is operating properly. When a control module stops communicating on the serial data circuit, for example if the module loses power or ground, the SOH message it normally sends on the serial data circuit disappears. Other control modules on the serial data circuit, which expect to receive that SOH message, detect its absence; those control modules in turn sets a DTC associated with the loss of SOH of the non-communicating control module. The DTC is unique to the control module which is not communicating, for example, when the inflatable restraint sensing and diagnostic module (SDM) SOH message disappears, several modules set DTC U1088. Note: a loss of serial data communications DTC does not represent a failure of the module that set it.

U0100 00
Lost Communication with Engine/Powertrain Control Module (ECM/PCM)

Circuit/System Verification
Verify that following BCM DTCs are not present:
• U1814
• U2099
• B1428
• B1370
• B1380
• B1440
• B1441
? If any listed DTC is present, refer to Diagnostic Trouble Code (DTC) List - Vehicle to diagnose that DTC prior to this diagnostic.

Circuit/System Testing
Note: Use the schematic to identify the following:
• Control modules the vehicle is equipped with
• Control module locations on the low and high speed GMLAN serial data circuits
• The control modules B+, ignition, ground, communication enable and serial data circuit terminals
Determine the module that is not communicating. Refer to Control Module U Code List.
Ignition OFF, disconnect the necessary harness connector of the module that is not communicating.
Test for less than 5 ? between each ground circuit terminal and ground.
? If greater than the specified range, test the ground circuit for an open/high resistance.
If equipped, verify that a test lamp illuminates between each B+ circuit terminal and ground.
? If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit fuse is open, test the control circuits of the control module for a short to ground. If the circuits test normal, replace the control module.
If equipped, ignition ON, verify that a test lamp illuminates between each ignition circuit terminal and ground.
? If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance. If the circuit fuse is open, test the control circuits of the control module for a short to ground. If the circuits test normal, replace the control module.
Note: Only the high speed GMLAN modules have a serial data communication enable circuit OR an accessory wakeup serial data circuit, and the BCM is the output for these circuits. Refer to the module schematics to identify which modules have these circuits.
If equipped, ignition ON, verify that a test lamp illuminates between the communication enable circuit terminal OR the accessory wakeup circuit terminal and ground.
? If the test lamp does not illuminate, test the circuit for an open/high resistance. If the circuits test normal, replace the BCM.
Ignition OFF for 60 seconds, test for less than 5 ? between the serial data circuit terminals and the DLC terminal listed below:
• Class 2 serial data circuit terminal 2
• Low speed GMLAN serial data terminal 1
• High speed GMLAN serial data terminal 6 or 14
? If greater than the specified range, test the serial data circuit for an open/high resistance between the non communicating control module and a module setting the DTC or a serial data splice pack.
If all circuits test normal, replace the control module that is not communicating.

DTC C0327 Encoder Circuit Malfunction - you have a electrical circuit problem ! I suggest you take this to a ASE certified repair facility . There is a very long diagnostic process to test this !
Circuit Description
The transfer case encoder is a switch that converts a shaft position, representing a mode or range position, into electrical signals for use by the transfer case shift control module. The encoder houses 4 Hall effect sensors that are used for channels P, A, B, and C. These sensors provide a path to ground, when a magnet, (part of the Motor Encoder), passes over them.
The transfer case shift control module supplies an 8 V reference and a ground circuit for the encoder hall effect sensors to function.
The transfer case shift control module supplies current limited 5 V on all the channels, thus as these channels are pulled to ground, the module can interpret the location of the transfer case shift position.
This DTC detects an open, short to ground, or a short to voltage (12 V) in the Encoder Feed Circuit, an open in the Signal Ground Circuit, an open, short to ground, or short to voltage (12 V) in the Encoder channel circuits.

What large square fuse ? The 4X4 switch get's it's B+ voltage from the four - wheel drive control module . computer controlled ! Has two relay's - transfercase hi to low & low to high ,located in the Auxiliary relay box #3 . location left side of radiator core support . Your best bet ,take it to a qualified repair shop that has a diagnostic tool that can communicate with the 4X4 control module . Read code's ! Probably has a code like one of these
P1812 Transmission 4-Wheel Drive Mode Select Circuit Failure 4WD control module Go To Pinpoint Test D . P1815 Transmission 4-Wheel Drive Mode Select Short Circuit to Ground 4WD control module Go To Pinpoint Test A .
But code have a few others as well .
B2105 Throttle Position Input Out of Range Low 4WD control module Go To Pinpoint Test B . B2106 Throttle Position Input Out of Range High 4WD control module Go To Pinpoint Test B . C1728 Transfer Case Unable to Transition Between 2H and 4H. 4WD control module Go To Pinpoint Test C . C1729 Transfer Case Unable to Transition Between 4WD HIGH and 4WD LOW 4WD control module Go To Pinpoint Test D . C1979 IWE Solenoid Circuit Failure 4WD control module Go To Pinpoint Test F . C1980 IWE Solenoid Short to Battery 4WD control module Go To Pinpoint Test F . P1812 Transmission 4-Wheel Drive Mode Select Circuit Failure 4WD control module Go To Pinpoint Test D . P1815 Transmission 4-Wheel Drive Mode Select Short Circuit to Ground 4WD control module Go To Pinpoint Test A . P1824 Transmission 4-Wheel Drive Clutch Relay Circuit Failure 4WD control module Go To Pinpoint Test A . P1826 Transmission 4-Wheel Drive Low Clutch Relay Short Circuit to Battery 4WD control module Go To Pinpoint Test A . P1827 Transmission 4-Wheel Drive Low Clutch Relay Short Circuit to Ground 4WD control module Go To Pinpoint Test A . P1849 Transmission Transfer Case Contact Plate A Short Circuit to Ground 4WD control module Go To Pinpoint Test D . P1853 Transmission Transfer Case Contact Plate B Short Circuit to Ground 4WD control module Go To Pinpoint Test D . P1857 Transmission Transfer Case Contact Plate C Short Circuit to Ground 4WD control module Go To Pinpoint Test D . P1861 Transmission Transfer Case Contact Plate D Short Circuit to Ground 4WD control module Go To Pinpoint Test D . P1867 Transmission Transfer Case Contact Plate General Circuit Failure 4WD control module Go To Pinpoint Test D . P1891 Transmission Transfer Case Contact Plate Ground Return Open Circuit 4WD control module Go To Pinpoint Test D .

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