Hummer H2. Manual - part 2656

DTC C0550 

SYMPTOMS - TRANSFER CASE 

Visual/Physical Inspection 

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Inspect for aftermarket devices which could affect the operation of the automatic transfer case system. 
Refer to Checking Aftermarket Accessories in Wiring Systems.  

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Inspect the easily accessible or visible system components for obvious damage or conditions which could 
cause the symptom.  

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Inspect the automatic transfer case for the proper fluid level.  

Intermittent 

Faulty electrical connections or wiring may be the cause of intermittent conditions. Refer to Testing for 
Intermittent Conditions and Poor Connections in Wiring Systems. 

Symptom List 

Refer to a symptom diagnostic procedure from the following list in order to diagnose the symptom: 

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Electronic Rear Differential Lock Will Not Engage  

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Electronic Rear Differential Lock Will Not Disengage  

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Transfer Case Shift Control Switch Inoperative  

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Transfer Case Shift Control Switch Indicator Always On - Two or More  

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Transfer Case Shift Control Switch Indicator Flashes, then Returns to Previous Mode  

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Transfer Case Shift Control Switch Indicator Inoperative - One or More  

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Service Indicator Always On  

Step

Action

Yes

No

Schematic Reference: Transfer Case Control Schematics 
Connector End View Reference: Transfer Case Control Connector End Views

1

Did you perform the Diagnostic System Check-Transfer 
Case?

Go to 

Step 2

Go to Diagnostic System 

Check - Transfer Case

2

Replace the transfer case shift control module. Refer to 
Transfer Case Shift Control Module Replacement . 
Is the repair complete?

System 

OK

-

IMPORTANT:

1. Perform the Transfer Case Diagnostic System Check before using the 

Symptom Tables in order to verify that the following statements are true: 

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DTCs are not set.  

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The control modules can communicate via the serial data link.  

2. Review the system operation in order to familiarize yourself with the 

system functions. Refer to Transfer Case Description and Operation .  

 

2004 Hummer H2 

2004 DRIVELINE/AXLE Transfer Case - BW 4484 - Hummer H2

  

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Service Indicator Inoperative  

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Transfer Case Popping Noise  

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Transfer Case Whine or Rumble Noise  

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Transfer Case Growl or Grinding Noise  

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Transfer Case Clunk in 4HI Lock  

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Transfer Case Clunk in 4LO Lock  

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Transfer Case Clunk during Acceleration and Deceleration  

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Transfer Case Shudder or Binding  

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Transfer Case Will Not Shift  

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Transfer Case Jumps Out of Gear  

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Transfer Case Leak Diagnosis  

TRANSFER CASE SHIFT CONTROL SWITCH INOPERATIVE 

Circuit Description 

The range/mode switch circuit consists of the following 5 switches: 

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4HI  

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4HI Lock  

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4LO Lock  

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Neutral  

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Differential Lock  

The transfer case shift control module supplies a regulated 5 volts, DC to the switch through the 5 volt regulator 
circuit. The current travel through the resistor of the currently active switch. The switch then returns current to 
the transfer case shift control module through the switch signal circuit. 

The transfer case shift control module constantly monitors this signal voltage to determine the condition of the 
mode switch circuit. 

When each switch is depressed, the switch will complete a circuit through the respective resistor. The transfer 
case shift control module continuously monitors the switch input to determine which of the following buttons 
were selected by the driver: 

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4HI  

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4HI Lock  

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4LO Lock  

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Differential Lock  

Test Description 

 

2004 Hummer H2 

2004 DRIVELINE/AXLE Transfer Case - BW 4484 - Hummer H2

  

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

2: This step tests the functionality of the mode switch.  

3: This step tests the modules ability to operate the transfer case modes.  

Transfer Case Shift Control Switch Inoperative 

TRANSFER CASE SHIFT CONTROL SWITCH INDICATOR ALWAYS ON - TWO OR MORE 

Circuit Description 

The indicator lamps circuit consist of the following 5 individual lamps contained inside the mode/range switch 
assembly: 

Step

Action

Yes

No

Schematic Reference: Transfer Case Control Schematics 
Connector End View Reference: Transfer Case Control Connector End Views

1

Did you perform the Diagnostic System Check-Transfer Case?

Go to 

Step 2

Go to Diagnostic 

System Check - 

Transfer Case

2

1. Install a scan tool.  

2. Start the engine.  

3. Place the transmission into neutral.  

4. Set the park brake.  

5. Observe the mode switch selected parameter on the scan tool 

while selecting each of the mode positions on the switch.  

Does the state change with the selection of each of the mode 
positions?

Go to 

Step 5

Go to Step 3

3

Test the switch signal and 5 volt reference circuits for an open, high 
resistance, short to ground, and short to voltage. Refer to Circuit 
Testing and Wiring Repairs in Wiring Systems. 
Did you find and correct the condition?

Go to 

Step 6

Go to Step 4

4

Replace the mode selection switch. Refer to Transfer Case Shift 
Control Switch Replacement . 
Did you complete the repair?

Go to 

Step 6

-

5

Replace the transfer case shift control module. Refer to Transfer 
Case Shift Control Module Replacement . 
Did you complete the repair?

Go to 

Step 6

-

6

1. Use the scan tool in order to clear the DTCs.  

2. Operate the vehicle in order to determine if the symptom has 

been corrected.  

Is the symptom still present?

Go to 

Step 2

System OK

 

2004 Hummer H2 

2004 DRIVELINE/AXLE Transfer Case - BW 4484 - Hummer H2

  

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4HI  

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4HI Lock  

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4LO Lock  

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Neutral  

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Differential Lock  

The following lamps are contained inside their respective mode button: 

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4HI  

z

4HI Lock  

z

4LO Lock  

z

Neutral  

z

Differential Lock  

When the ignition in ON, the transfer case shift control module illuminates the indicator that corresponds to the 
current gear position by providing a ground through a current limiting driver. 

The transfer case shift control module flashes each indicator lamp after a shift has been requested and will 
continue to flash until the transfer case shift control module can complete the shift. 

A solid state circuit located inside the switch supplies ignition voltage to the lamps. The solid state circuit also 
receives voltage whenever the headlamp switch is in the parklamp or headlamp position. When the solid state 
circuit receives voltage from the headlamp switch, the switch reduces the voltage supplied to the indicator 
lamps, dimming the lamps when the headlamps are ON. 

Test Description 

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

2: This step tests the transfer case electrical control of the lamp circuits.  

3: This step tests the suspect lamp circuits for a short to ground.  

Transfer Case Shift Control Switch Indicator Always On - Two or More 

Step

Action

Yes

No

Schematic Reference: Transfer Case Control Schematics 
Connector End View Reference: Transfer Case Control Connector End Views

1

Did you perform the Diagnostic System Check-Transfer 
Case?

Go to 

Step 2

Go to Diagnostic System 

Check - Transfer Case

2

1. Turn the ignition ON, with the engine OFF.  

2. Install a scan tool.  

3. Use the scan tool in order to command all the indicator 

lamps OFF.  

Go to 

 

2004 Hummer H2 

2004 DRIVELINE/AXLE Transfer Case - BW 4484 - Hummer H2