Hummer H2. Manual — part 234

DTC U1000

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. When a module does not
associate an identification number with at least one critical parameter within 5 seconds of beginning serial data
communication, DTC U1000 is set. When more than one critical parameter does not have an identification
number associated with it, the DTC will only be reported once.

The class 2 serial data line on this vehicle is a star configuration, with the body control module (BCM) and
powertrain control module (PCM) each have a second class 2 serial data line between them. The following
modules communicate on the class 2 serial data line:

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The audio amplifier

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The body control module (BCM)

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The driver door module (DDM)

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The driver seat module (DSM)

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The electronic brake control module (EBCM)

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The electronic suspension control (ESC) module

U1040 DTC U1001-U1254

ESC, IPC, PCM, SDM

U1057 DTC U1001-U1254

BCM, IPC

U1064 DTC U1001-U1254

DDM, ESC, FPDM, HVAC, IPC, PCM, Radio, RSA, SDM, VCIM

U1088 DTC U1001-U1254

VCIM

U1096 DTC U1001-U1254

BCM, SDM

U1128 DTC U1001-U1254

Audio Amplifier, RSA

U1129 DTC U1001-U1254

Radio

U1151 DTC U1001-U1254

Radio

U1152 DTC U1001-U1254

BCM

U1160 DTC U1001-U1254

BCM, DSM, ESC, FPDM

U1161 DTC U1001-U1254

BCM, DDM, DSM, ESC

U1166 DTC U1001-U1254

DDM

U1167 DTC U1001-U1254

Radio

U1300

DTC U1300, U1301,
or U1305

EBCM, ESC, HVAC, IPC, PCM, Radio, RSA, SDM, VCIM

U1301

DTC U1300, U1301,
or U1305

EBCM, ESC, HVAC, IPC, PCM, Radio, RSA, SDM, VCIM

U1305

DTC U1300, U1301,
or U1305

Audio Amplifier, BCM, DDM, DSM, FPDM, TCSCM
or

2004 Hummer H2

2004 ACCESSORIES & EQUIPMENT Data Link Communications - Hummer H2

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The front passenger door module (FPDM)

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The HVAC control module

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The inflatable restraint sensing and diagnostic module (SDM)

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The instrument panel cluster (IPC)

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The powertrain control module (PCM)

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The radio

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The rear seat audio (RSA) controller

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The transfer case shift control module (TCSCM)

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The vehicle communication interface module (VCIM) w/UE1

Conditions for Running the DTC

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Voltage supplied to the module is in the normal operating voltage range of 9-16 volts.

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DTCs U1300, U1301 or U1305 do not have a current status.

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The vehicle power mode requires serial data communication to occur.

Conditions for Setting the DTC

A node alive message has not been received from an unidentified module within the last 5 seconds after
establishing class 2 serial data communication.

Action Taken When the DTC Sets

The module uses a default value for the missing parameter.

Conditions for Clearing the DTC

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

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

Diagnostic Aids

When a malfunction occurs while modules are communicating, a lost communication DTC is set as a current
DTC. When the modules stop communicating the current lost communication DTC is cleared but the history
DTC remains. When the modules begin to communicate again, the module with the open fuse will not be
learned by the other modules so U1000 is set current by the other modules. If the malfunction occurs when the
modules are not communicating, only U1000 is set.

Test Description

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

1: A DTC U1001 - U1254 Lost Communications with XXX with a history status may indicate the cause

2004 Hummer H2

2004 ACCESSORIES & EQUIPMENT Data Link Communications - Hummer H2

of U1000.

2: The modules not communicating are the likely cause of U1000. The modules that are available on the
class 2 serial data circuit are listed in the Circuit Description.

6: The module which was not communicating due to a poor connection to the class 2 serial data circuit
may have set DTC U1001 - U1254 Lost Communications with XXX for those modules that it was
monitoring.

9: The modules which can communicate indicate the module which cannot communicate. You must clear
the serial data communication DTCs from these modules to avoid future misdiagnosis.

12: If all modules are communicating, the module which set U1000 may have done so due to some other
condition.

14: The module which set U1000 is the likely cause of the malfunction.

DTC U1000

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

1. Install a scan tool.

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

3. Record the DTCs set in by each module. If using a

Tech 2, use the Class 2 DTC Check feature to
determine which modules have DTCs set.

Did you record any DTCs in the range of U1001-U1254
with a history status?

Go to Diagnostic Trouble

Code (DTC) List

Go to Step

2

2

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

2. Attempt to communicate with each module on the

class 2 serial data circuit. If using a Tech 2, obtain
this information using the class 2 Message Monitor
feature.

3. Record all of the modules communicating on the

class 2 serial data circuit.

4. Compare the list of modules which are

communicating to the list given in Circuit
Description.

Does any module on the class 2 serial data circuit not
communicate?

Go to Step 3

Go to Step

12

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

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The battery positive voltage supply circuits

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The switched battery positive supply circuits

2004 Hummer H2

2004 ACCESSORIES & EQUIPMENT Data Link Communications - Hummer H2

3

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The battery positive voltage output circuits

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The ignition voltage input circuits

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The ignition voltage output circuits

Refer to the following:

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Control Module References in Body Control
System for the applicable schematic

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Circuit Testing in Wiring Systems

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Wiring Repairs in Wiring Systems

Did you find and correct the condition?

Go to Step 8

Go to Step

4

4

1. Turn OFF the ignition.

2. Test the ground circuits of the module that is not

communicating for an open. Refer to the following:

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Control Module References in Body
Control System for the applicable schematic

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Circuit Testing in Wiring Systems

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Wiring Repairs in Wiring Systems

Did you find and correct the condition?

Go to Step 8

Go to Step

5

5

1. Turn OFF the ignition.

2. Test the class 2 serial data circuits of the module

that is not communicating for an open. Refer to the
following:

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Data Link Connector (DLC) Schematics

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Circuit Testing in Wiring Systems

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Wiring Repairs in Wiring Systems

Did you find and correct the condition?

IMPORTANT:

Inspect all connectors in the serial data
communications circuit.
Refer to the following:

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Data Link Connector (DLC) Schematics

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Testing for Intermittent Conditions and Poor
Connections in Wiring Systems

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Connector Repairs in Wiring Systems

Go to Step 8

Go to Step

6

2004 Hummer H2

2004 ACCESSORIES & EQUIPMENT Data Link Communications - Hummer H2