Hummer H1 (2006+). Manual - part 157

OBD-472

On-Board Diagnostics

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DTC U0073 High Speed CAN Communication Bus (Figure OBD-120)

Figure OBD-120:   CAN Communication Bus Circuit

Circuit Description

Modules connected to the controller area network (CAN) serial data circuits monitor for serial data communications during normal
vehicle operation. Operating information and commands are exchanged among the modules. If no communication is detected on

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 On-Board Diagnostics  OBD-473

5745804

CAN serial data circuit, the DTC is set. A total non communication condition may be caused by a short to battery or voltage on any
of the CAN circuits or a short between the CAN high and low circuits.

The following modules communicate on CAN serial data (LLY engine):

• The engine control module (ECM) 

• The transmission control module (TCM) 

• The fuel injector control module (FICM) 

• The glow plug controller module (GPCM) 

Conditions for Setting the DTC

A total non communication condition is detected on CAN serial data circuit.

Action Taken When the DTC Sets 

• The module uses a default value for the missing parameter. 

• The malfunction indicator lamp (MIL) will illuminate on the second consecutive ignition cycle that the diagnostic runs and 

fails, for the type B DTCs. For a detailed description about DTC types, refer to Diagnostic Trouble Code (DTC) Type 
Definitions in Engine Controls - 6.6L (LLY). 

Conditions for Clearing the MIL/DTC

The MIL/DTC clearing depends on DTC type. For information about DTC types, refer to Diagnostic Trouble Code (DTC) Type(s)
in Engine Controls - 6.6L (LLY).

DTC Type B 

• The MIL clears after 3 ignition cycles when the malfunction is no longer present. 

• A current DTC clears when the malfunction is no longer present. 

• A history DTC clears when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunc-

tion.

Step

Action

Value(s)

Yes

No

    1

Did you perform the Diagnostic System Check - Vehicle?

Go to Step 2

Go to Diagnos-

tic System 

Check

    2

1.

Observe the Freeze Frame/Failure Records for this DTC.

2.

Turn OFF the ignition for 30 seconds.

3.

Start the engine.

4.

Operate the vehicle within the Conditions for Running the 
DTC. You may also operate the vehicle within the conditions 
that you observed from the Freeze Frame/Failure Records.

Does the DTC fail this ignition?

Go to Step 3 

Go to Testing 

for Intermittent 
Conditions and 

Poor Connec-

tions

    3

1.

Turn OFF the ignition.

2.

Disconnect the fuel injector control module (FICM).

3.

Disconnect the CAN circuits from the FICM.

4.

Reconnect the FICM.

5.

Operate the vehicle within the Conditions for Running the 
DTC.

6.

Retrieve DTCs from engine control module (ECM) and 
transmission control module (TCM).

Does the DTC reset as current in any module?

Go to Step 4

Go to Step 7

OBD-474

On-Board Diagnostics

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    4

1.

Turn OFF the ignition.

2.

Disconnect the glow plug control module (GPCM).

3.

Disconnect the CAN circuits from the GPCM.

4.

Reconnect the GPCM.

5.

Operate the vehicle within the Conditions for Running the 
DTC.

6.

Retrieve DTCs from ECM and TCM.

Does the DTC reset as current in any module?

Go to Step 5

Go to Step 7

    5

NOTE:

• If the vehicle is not equipped with TCM skip to the next 

step.

• If the code set only in TCM, disconnect the ECM in this 

step.

• If the code was set by ECM or by both modules, discon-

nect the TCM in this step. 

1.

Turn OFF the ignition.

2.

Disconnect the module conform to the important statement.

3.

Disconnect the CAN circuits from the module.

4.

Reconnect the module.

5.

Operate the vehicle within the Conditions for Running the 
DTC.

6.

Retrieve DTCs from the module still connected.

Does the DTC reset as current?

Go to Step 6 

Go to Step 7

    6

NOTE: Turn ON the ignition, with the engine OFF, when testing
for a short to voltage. Use DVOM MIN/MAX function to capture
intermittent conditions.

1.

Turn OFF the ignition.

2.

Disconnect the last module still connected to CAN bus.

3.

Test the CAN serial data circuits for a short to ground, short 
to voltage, an open, or a short between them. 

• Testing for Intermittent Conditions and Poor Connections 

• Circuit Testing 

• Connector Repairs 

• Wiring Repairs 

Did you find and correct the condition?

Go to Step 9 

Go to Step 7

    7

Inspect for an intermittent or poor connections at the last discon-
nected/reconnected module.

Did you find and correct the condition?

Go to Step 9

Go to Step 8

    8

NOTE: Perform the module setup procedure if required.

Replace the last disconnected/reconnected module. 

Did you complete the replacement?

Go to Step 9 

Step

Action

Value(s)

Yes

No

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 On-Board Diagnostics  OBD-475

5745804

    9

1.

Reconnect all wires and modules.

2.

Clear the DTCs with a scan tool.

3.

Turn OFF the ignition for 30 seconds.

4.

Start the engine.

5.

Operate the vehicle within the Conditions for Running the 
DTC. You may also operate the vehicle within the conditions 
that you observed from the Freeze Frame/Failure Records.

Did the DTC fail this ignition?

Go to Step 3 

System OK

Step

Action

Value(s)

Yes

No