Hummer H3. Manual — part 1651

DTC C0550

Circuit Description

At each power-up the transfer case shift control module runs a self-test on the following
functions:

EEPROM Checksum

ROM Checksum

RAM Checksum

RAM Malfunction

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC C0550 ECU Malfunction

Conditions for Running the DTC

The ignition is ON.

The system voltage is 9-18 volts.

Conditions for Setting the DTC

Critical operational parameters stored in EEPROM have failed Checksum test indicating
invalid data.

Masked ROM code has failed Checksum test indicating that masked ROM data is not
currently valid.

ROM code has failed Checksum test indicating that ROM data is not currently valid.

Did you complete the repair?

Go to Step 8

8

1. Use the scan tool in order to

clear the DTCs.

2. Operate the vehicle within the

Conditions for Running the
DTC as specified in the
supporting text.

Does the DTC reset?

-

Go to Step 2 System OK

2007 Hummer H3

2007 TRANSMISSION Transfer Case - BW 4493/4494 - H3

One or more ROM locations have failed operational test indicating that some portions of
RAM are not functional.

Action Taken When the DTC Sets

The SERVICE 4WD indicator will be latched on and the system will be disabled.

The transfer case control switch will display the current position LED while DTC C0550 is
current, but further shifting will be disabled.

Conditions for Clearing the DTC

Replace the transfer case shift control module.

Perform the Diagnostic System Check - Vehicle.

Test Description

The number below refers to the step number on the diagnostic table.

2: This step replaces the transfer case shift control module.

DTC C0550

SYMPTOMS - TRANSFER CASE

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 - Vehicle?

Go to Step 2

Go to
Diagnostic
System Check
- Vehicle

2

Replace the transfer case shift control
module. Refer to Control Module
References for replacement, setup and
programming.
Is the repair complete?

System OK

-

IMPORTANT:

1. Perform the Diagnostic System Check - Vehicle before using

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

There are no diagnostic trouble codes (DTCs) present.

2007 Hummer H3

2007 TRANSMISSION Transfer Case - BW 4493/4494 - H3

Visual/Physical Inspection

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

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

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 .

Symptom List

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

Electronic Rear Differential Lock Will Not Engage

Electronic Rear Differential Lock Will Not Disengage

Transfer Case Shift Control Switch Inoperative

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

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

Transfer Case Shift Control Switch Indicator Inoperative - One or More

Service Indicator Always On

Service Indicator Inoperative

Transfer Case Popping Noise

Transfer Case Whine or Rumble Noise

Transfer Case Growl or Grinding Noise

Transfer Case Clunk in 4HI Lock

The control module or 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.

2007 Hummer H3

2007 TRANSMISSION Transfer Case - BW 4493/4494 - H3

Transfer Case Clunk in 4LO Lock

Transfer Case Clunk during Acceleration and Deceleration

Transfer Case Shudder or Binding

Transfer Case Will Not Shift

Transfer Case Jumps Out of Gear

Transfer Case Leak Diagnosis

TRANSFER CASE SHIFT CONTROL SWITCH INOPERATIVE

Circuit Description

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

4HI

4HI Lock

4LO Lock

Differential Lock

Neutral

The transfer case shift control module supplies a regulated 5 volts, DC, to the switch through the
5 volt regulator circuit. The current travels through the resistor of the currently active switch. The
switch then returns the 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 is selected by the driver:

4HI

4HI Lock

4LO Lock

Differential Lock

Test Description

2007 Hummer H3

2007 TRANSMISSION Transfer Case - BW 4493/4494 - H3