Hummer H2. Manual — part 235

6

Inspect the harness connector of the module that is not
communicating for poor connections and terminal tension
at the following circuits:

z

The battery positive voltage input circuits

z

The switched battery positive voltage supply

z

The battery positive voltage output circuits

z

The ignition voltage input circuits

z

The ignition voltage output circuits

z

The ground circuits

z

The class 2 serial data circuits

Refer to the following:

z

Control Module References in Body Control
System for the applicable schematic

z

Testing for Intermittent Conditions and Poor
Connections in Wiring Systems

z

Connector Repairs in Wiring Systems

Did you find and correct the condition?

Go to Step 8

Go to Step

7

7

Replace the module that is not communicating. Refer to
Control Module References in Body Control System for
the appropriate Repair Instructions for the module
replacement.Did you complete the replacement?

IMPORTANT:

Perform the module programming or setup procedure
if required.

Go to Step 10

-

8

1. Install a scan tool.

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

3. Select the Display DTCs function for the module

which was not communicating.

Does the scan tool display any DTCs which do not begin
with a "U"?

Go to Control Module

References in Body

Control System for

applicable Diagnostic

System Check

Go to Step

9

9

Use the scan tool in order to clear the DTCs.
Did you complete the action?

Go to Step 10

-

10

Select the Display DTCs function for the modules which
had U1000 set as a current DTC.
Does the scan tool display DTCs which do not begin with

Go to Control Module

References in Body

Control System for

2004 Hummer H2

2004 ACCESSORIES & EQUIPMENT Data Link Communications - Hummer H2

DTC U1001-U1254

Circuit Description

Modules connected to the class 2 serial data circuit monitor for serial data communications during normal
vehicle operation. Operating information and commands are exchanged among the modules. When a module
receives a message for a critical operating parameter, the module records the identification number of the
module which sent the message for State of Health monitoring. A critical operating parameter is one which,
when not received, requires that the module use a default value for that parameter. Once an identification
number is learned by a module, it will monitor for that module's Node Alive message. Each module on the class
2 serial data circuit which is powered and performing functions that require detection of a communications
malfunction is required to send a Node Alive message every 2 seconds. When no message is detected from a
learned identification number for 5 seconds, a DTC U1xxx where xxx is equal to the 3-digit identification
number is set.

The control module ID number list below provides a method for determining which module is not
communicating. A module with a class 2 serial data circuit malfunction or which loses power during the current

a "U"?

applicable Diagnostic

System Check

Go to Step

11

11

Use the scan tool in order to clear the DTCs.
Did you complete the action?

System OK

-

12

Did you record any other DTCs for the modules which
had U1000 set as a current DTC?

Go to Control Module

References in Body

Control System for

applicable Diagnostic

System Check

Go to Step

13

13

1. Install a scan tool.

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

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

4. Turn OFF the ignition for at least 5 seconds.

5. Turn ON the ignition with the engine OFF.

6. Select the Display DTCs function.

Does the scan tool display U1000 set as a current DTC?

Go to Step 14

Go to

Diagnostic

Aids

14 Replace the module which had U1000 set as a current

DTC. Refer to Control Module References in Body
Control System for the appropriate Repair Instructions for
the module replacement.Did you complete the
replacement?

IMPORTANT:

Perform the module programming or setup procedure
if required.

System OK

-

2004 Hummer H2

2004 ACCESSORIES & EQUIPMENT Data Link Communications - Hummer H2

ignition cycle will have a Loss of Communication DTC set by other modules that depend on information from
that failed module. The modules that can communicate will set a DTC indicating the module that can not
communicate.

DTC U1001-U1254

When more than one Loss of Communication DTC is set in either 1 module or in several modules, diagnose the
DTCs in the following order:

1. Current DTCs before history DTCs unless told otherwise in the diagnostic table.

2. The DTC which is reported the most times.

3. From the lowest number DTC to the highest number DTC.

Conditions for Running the DTC

z

The following diagnostic trouble codes do not have a current status:

{

U1300

{

U1301

{

U1305

z

The vehicle power mode requires serial data communication to occur.

Conditions for Setting the DTC

A message from a learned identification number has not been detected for the past 5 seconds.

Action Taken When the DTC Sets

Control Module

ID Number

Powertrain Control Module (PCM)

016

Transfer Case Shift Control Module (TCSCM)

026

Electronic Brake Control Module (EBCM)

040

Air Suspension Module (ESC)

057

Body Control Module (BCM)

064

Inflatable Restraint Sensing and Diagnostic Module (SDM)

088

Instrument Panel Cluster (IPC)

096

Radio

128

Audio Amplifier

129

Vehicle Communications Interface Module (VCIM)

151

HVAC Control Module

152

Driver Door Module (DDM)

160

Front Passenger Door Module (FPDM)

161

Driver Seat Module (DSM)

166

Rear Seat Audio (RSA) Control

167

2004 Hummer H2

2004 ACCESSORIES & EQUIPMENT Data Link Communications - Hummer H2

The module uses a default value for the missing parameter.

Conditions for Clearing the DTC

z

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

z

A history DTC clears when the module ignition cycle counter reaches the reset threshold, without a repeat
of the malfunction.

Diagnostic Aids

z

An intermittent open between the inoperative module and a star connector may cause this code to set.

z

A poor connection at the inoperative module or a star connector may cause this code to set.

z

An intermittent open in a star connector may cause this code to set.

z

An improperly powered module may cause this code to set.

Test Description

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

6: The module which was not communicating on the class 2 serial data circuit may have set Loss of
Communication DTCs for those modules that it was monitoring.

DTC U1001-U1254

Step

Action

Yes

No

Schematic Reference: Data Link Connector (DLC) Schematics
Connector End View Reference: Master Electrical Component List and Inline Harness Connector
End Views in Wiring Systems

1

Test the following circuits of the module that is not
communicating for an open or a short to ground:

z

The battery positive voltage input circuits

z

The battery positive voltage output circuits

z

The ignition voltage input circuits

z

The ignition voltage output circuits

z

The switched battery positive voltage circuits

Refer to the following:

z

Control Module References in Body Control System
for the applicable schematic

IMPORTANT:

Use the control module ID number list in order to
determine which module is not communicating.

2004 Hummer H2

2004 ACCESSORIES & EQUIPMENT Data Link Communications - Hummer H2