Hummer H2. Manual — part 732

DIAGNOSTIC INFORMATION AND PROCEDURES

DIAGNOSTIC STARTING POINT - HORNS

Begin the system diagnosis with Diagnostic System Check - Horns . The Diagnostic System Check will
provide the following information:

z

The identification of the control module(s) which command the system

z

The ability of the control module(s) to communicate through the serial data circuit

z

The identification of any stored diagnostic trouble codes (DTCs) and their status

The use of the Diagnostic System Check will identify the correct procedure for diagnosing the system and
where the procedure is located.

DIAGNOSTIC SYSTEM CHECK - HORNS

Test Description

The number(s) below refer to the step number(s) on the diagnostic table.

2: Lack of communication may be due to a partial malfunction of the class 2 serial data circuit or due to a
total malfunction of the class 2 serial data circuit. The specified procedure will determine the particular
condition.

4: The presence of DTCs which begin with "U" indicate some other module is not communicating. The
specified procedure will compile all the available information before tests are performed.

Diagnostic System Check - Horns

Step

Action

Yes

No

1

Install a scan tool.
Does the scan tool power up?

Go to Step 2

Go to Scan Tool Does Not

Power Up in Data Link

Communications

2

1. Turn ON the ignition, with

the engine OFF.

2. Attempt to establish

communication with the
body control module
(BCM).

Does the scan tool communicate
with the body control module?

Go to Step 3

Go to Scan Tool Does Not

Communicate with Class 2

Device in Data Link

Communications

3

Select the body control module
display DTCs function on the
scan tool.
Does the scan tool display any
DTCs?

Go to Step 4

Go to Symptoms - Horns

2004 Hummer H2

2004 ACCESSORIES & EQUIPMENT Horns - Hummer H2

DIAGNOSTIC TROUBLE CODE (DTC) LIST

Diagnostic Trouble Code (DTC) List

DTC B2752

Circuit Description

The vehicle horns are activated whenever ground is applied to the horn relay coil through the horn relay control
circuit. Ground may be applied by either of the following:

z

Body control module (BCM)

z

Horn switch

Conditions for Running the DTC

z

The body control system voltage must be between 9.0 and 16.0 volts.

z

The BCM is commanding the horn relay on or the horn switch is pressed.

Conditions for Setting the DTC

The BCM detects a short to ground or an open in the horn relay control circuit for approximately 3 minutes.

Action Taken When the DTC Sets

z

If the horn relay control circuit is shorted to ground the horns will remain ON at all times.

z

If the horn relay control circuit is open the horn will only work with the horn button on the steering
wheel.

z

The BCM stores DTC B2752 in memory.

Conditions for Clearing the DTC

4

Does the scan tool display any
DTCs which begin with a "U"?

Go to Scan Tool Does Not

Communicate with Class 2

Device in Data Link

Communications

Go to Step 5

5

Does the scan tool display DTC
B1000, B1004, B1007, or
B1009?

Go to Diagnostic Trouble

Code (DTC) List in Body

Control System

Go to Step 6

6

Does the scan tool display DTC
B1327 or B1328?

Go to Diagnostic Trouble

Code (DTC) List in Engine

Electrical

Go to Diagnostic Trouble

Code (DTC) List

DTC

Diagnostic Procedure

Module(s)

B2752

DTC B2752

BCM

2004 Hummer H2

2004 ACCESSORIES & EQUIPMENT Horns - Hummer H2

z

A current DTC will clear when the fault is no longer present and the ignition is cycled.

z

A history DTC will clear after 100 consecutive ignition cycles without a fault present.

z

A scan tool may be used to clear history and current DTC(s).

Diagnostic Aids

z

Always begin diagnosis with the first DTC listed on the scan tool.

z

The scan tool must display DTC B2752 as a current code before performing these diagnostics.

z

Inspect for a sticking horn pad and or switch.

z

Perform a visual inspection for loose or poor connections at all related components.

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

Test Description

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

2: Listen for an audible click when the horn relay operates. Command both the ON and OFF states.
Repeat the commands as necessary.

3: Tests for voltage at the coil side of the horn relay. The HORN fuse supplies power to the coil side of
the horn relay.

4: Verifies that the body control module (BCM) is providing ground to the horn relay.

5: Tests if ground is constantly being applied to the horn relay.

DTC B2752

Step

Action

Yes

No

Schematic Reference:Horns Schematics

1

Did you perform the Horns Diagnostic System Check?

Go to Step 2

Go to Diagnostic

System Check -

Horns

2

1. Install a scan tool.

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

3. With a scan tool, command the horn relay ON and OFF.

Does the horn relay turn ON and OFF with each command?

Go to

Diagnostic

Aids

Go to Step 3

3

1. Turn OFF the ignition.

2. Disconnect the horn relay.

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

4. Connect a test lamp between the battery positive voltage

circuit of the horn relay coil and a good ground.

Does the test lamp illuminate?

Go to Step 4

Go to Step 10

2004 Hummer H2

2004 ACCESSORIES & EQUIPMENT Horns - Hummer H2

SYMPTOMS - HORNS

4

1. Connect a test lamp between the control circuit of the horn

relay and the battery positive voltage circuit of the horn
relay coil.

2. With a scan tool, command the horn relay ON and OFF.

Does the test lamp turn ON and OFF with each command?

Go to Step 8

Go to Step 5

5

Does the test lamp remain illuminated with each command?

Go to Step 7

Go to Step 6

6

Test the control circuit of the horn relay for an open. Refer to
Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?

Go to Step

13

Go to Step 9

7

Test the control circuit of the horn relay for a short to ground.
Refer to Circuit Testing and Wiring Repairs in Wiring
Systems.
Did you find and correct the condition?

Go to Step

13

Go to Step 9

8

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

Go to Step

13

Go to Step 11

9

Inspect for poor connections at the harness connector of the body
control module (BCM). Refer to Testing for Intermittent
Conditions and Poor Connections and Connector Repairs in
Wiring Systems.
Did you find and correct the condition?

Go to Step

13

Go to Step 12

10

Repair the battery positive voltage circuit of the horn relay coil.
Refer to Wiring Repairs in Wiring Systems.
Did you complete the repair?

Go to Step

13

-

11

Replace the horn relay.
Did you complete the replacement?

Go to Step

13

-

12

Replace the BCM. Refer to Body Control Module
Replacement in Body Control System.Did you complete the
replacement?

IMPORTANT:

Perform the BCM programming procedure when replacing the
BCM.

Go to Step

13

-

13

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

IMPORTANT: The following steps must be completed before using the symptom tables.

2004 Hummer H2

2004 ACCESSORIES & EQUIPMENT Horns - Hummer H2