Hummer H2. Manual - part 237

SCAN TOOL DOES NOT COMMUNICATE WITH CLASS 2 DEVICE

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. Connecting a scan
tool to the DLC allows communication with the modules for diagnostic purposes.

Diagnostic Aids

The engine will not start when there is a total loss of class 2 serial data communication while the ignition is
OFF. The following conditions will cause a total loss of class 2 serial data communication:

A class 2 serial data circuit shorted to ground.

A class 2 serial data circuit shorted to voltage.

An internal condition within a module or connector on the class 2 serial data circuit, that causes a short to
voltage or ground to the class 2 serial data circuit.

Test Description

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

2: A partial malfunction in the class 2 serial data circuit uses a different procedure from a total
malfunction of the class 2 serial data circuit. The following modules communicate on the class 2 serial
data circuit:

Air Suspension Module (ESC)

Audio Amplifier (early production), refer to Radio/Audio System Description and Operation in
Entertainment for more information.

BCM

DDM

DSM

Test the ground circuit from pin 4 of the DLC for an
open or high resistance. Refer to Circuit Testing or
Wiring Repairs in Wiring Systems.
Did you find and correct the condition?

Go to Control Module

References in Body Control

System for the applicable

Diagnostic System Check

Go to

Step 3

Inspect for poor connections and terminal tension at the
DLC. Refer to Testing for Intermittent Conditions
and Poor Connections or Connector Repairs in
Wiring Systems.
Did you find and correct the condition?

Go to Control Module

References in Body Control

System for the applicable

Diagnostic System Check

Go to

Step 4

The scan tool may be malfunctioning. Refer to the scan
tool user guide.
Did you obtain a properly operating scan tool?

Go to Control Module

References in Body Control

System for the applicable

Diagnostic System Check

2004 Hummer H2

2004 ACCESSORIES & EQUIPMENT Data Link Communications - Hummer H2

EBCM

FPDM

HVAC Control Module

IPC

PCM

Radio

RSA Module

SDM

TCSCM

VCIM

3: The following DTCs may be retrieved with a history status, but are not the cause of the present
condition.

U1300

U1301

U1305

6: A state of health DTC with a history status may be present along with a U1000 or U1255 code having
a current status. This indicates that the malfunction occurred when the ignition was ON.

7: Data link connector terminals 2 and 5 provide the connection to the class 2 serial data circuit and the
signal ground circuit respectively.

10: A poor connection at DLC terminal of the splice pack - SP205 would cause this condition but will not
set a DTC.

11: An open in the class 2 serial data circuit between the DLC and splice pack - SP205 will prevent the
scan tool from communicating with any module. This condition will not set a DTC.

12: The class 2 serial data circuit is shorted to voltage or ground. The condition may be due to the wiring
or due to a malfunction in one of the modules. When testing the wire for a short, make sure there is not a
module connected to the wire being tested. This test isolates the BCM and the PCM class 2 serial data
circuits.

13: This test isolates the BCM class 2 serial data circuits.

16: The BCM detects that the ignition is ON and sends the appropriate power mode message to the other
modules. Therefore, the BCM must remain connected to the DLC for any other module to communicate
with the scan tool. This test isolates the splice pack - SP207 serial data circuits.

21: This test isolates the splice pack - SP206 serial data circuits and radio.

28: This test isolates the EBCM and TCSCM class 2 serial data circuits.

32: This test isolates the rest of the splice pack - SP205 serial data circuits.

36: If there are no current DTCs that begin with a "U", the communication malfunction has been repaired.

37: The communication malfunction may have prevented diagnosis of the customer complaint.

Scan Tool Does Not Communicate with Class 2 Device

Step

Action

Yes

Schematic Reference:Data Link Connector (DLC) Schematics

2004 Hummer H2

2004 ACCESSORIES & EQUIPMENT Data Link Communications - Hummer H2

Connector End View Reference:Master Electrical Component List and Inline Harness Connector
End Views in Wiring Systems

Does the scan tool power up?

Go to Step 2

Go to Scan

Tool Does

Not Power

1. Turn ON the ignition leaving 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.

Does the scan tool communicate with any module on the
class 2 serial data circuit?

Go to Step 3

Go to Step

1. Select the Display DTCs function for each module. If

using a Tech 2, use the Class 2 DTC Check feature in
order to determine which modules do have DTCs set.

2. Record all of the displayed DTCs, the DTC status and

the module which set the DTC.

Did you record any DTCs in the range of U1000 to U1305?

Go to Step 4

Go to Step

Are the history DTCs U1300, U1301 or U1305 retrieved
from any module?

Go to Step 5

Go to Step

Test the class 2 serial data circuit for an intermittent short to
ground or an intermittent short to voltage. Refer to the
following:

Testing for Intermittent Conditions and Poor
Connections

Circuit Testing

Connector Repairs

Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

IMPORTANT:

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

Go to Step 36

Go to Step

Is U1000 or U1255 the only DTC displayed in the
previously specified range?

Go to DTC U1000

Go to DTC

U1001-

U1254

Diagnose the non-communicating module by using the DTC
U1001-U1254 procedure for the module which is not

Go to Control Module

References in Body

2004 Hummer H2

2004 ACCESSORIES & EQUIPMENT Data Link Communications - Hummer H2

communicating. Refer to

DTC U1001-U1254

Did you complete the action?

Control System for the

applicable Diagnostic

System Check

1. Turn OFF the ignition.

2. Disconnect the scan tool from the data link connector

(DLC).

3. Inspect for poor connections at the DLC terminals 2

and 5. Refer to Testing for Intermittent Conditions
and Poor Connections and Connector Repairs in
Wiring Systems.

Did you find and correct the condition?

Go to Control Module

References in Body

Control System for the

applicable Diagnostic

System Check

Go to Step

Test the DLC ground circuit at terminal 5 for an open. Refer
to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?

Go to Control Module

References in Body

Control System for the

applicable Diagnostic

System Check

Go to Step

1. Disconnect the splice pack - SP205.

2. Inspect for poor connections at the splice pack -

SP205. Refer to Testing for Intermittent Conditions
and Poor Connections and Connector Repairs in
Wiring Systems.

Did you find and correct the condition?

Go to Control Module

References in Body

Control System for the

applicable Diagnostic

System Check

Go to Step

Test the class 2 serial data circuit between the DLC and the
splice pack - SP205 for an open, a short to ground, or a short
to voltage. Turn ON the ignition leaving the engine OFF
when testing for a short to voltage. Refer to Circuit Testing
and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?

Go to Control Module

References in Body

Control System for the

applicable Diagnostic

System Check

Go to Step

1. Using the correct terminal adapter, connect a jumper

wire to the DLC terminal of the splice pack - SP205.

2. Connect the other end of the jumper wire, using

correct terminal adapter, to the BCM terminal of the
splice pack - SP205.

3. Turn ON the ignition leaving the engine OFF.

4. Attempt to communicate with the BCM.

Does the scan tool communicate with the BCM?

Go to Step 16

Go to Step

1. Turn OFF the ignition.

2. Disconnect the PCM.

3. Turn ON the ignition leaving the engine OFF.

2004 Hummer H2

2004 ACCESSORIES & EQUIPMENT Data Link Communications - Hummer H2

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