Hummer H2. Manual - part 733

1. Perform Diagnostic System Check - Horns before using the symptom tables in order to verify that all of 

the following are true: 

z

There are no DTCs set.  

z

The body control module (BCM) can communicate via the serial data link.  

2. Review the system operation in order to familiarize yourself with the system functions. Refer to Horns 

System Description and Operation .  

Visual/Physical Inspection 

Several of the symptom procedures ask for a careful visual/physical inspection. This step is extremely 
important, it could lead to correcting a problem without further checks and can save valuable time. These 
checks include the following: 

z

Inspect for aftermarket devices which could affect the operation of the Horn System. Refer to Checking 
Aftermarket Accessories in Wiring Systems.  

z

Inspect the easily accessible or visible system components and harness connectors for obvious damage or 
conditions which could cause the symptom. 

z

Perform the following if the horns buzz or have a harsh tone: 

{

Inspect for debris in the joints where the horns fasten to the vehicle.  

{

Test the torque of the horn mounting hardware. The horn mounting hardware should be tightened to
a torque of 10 N.m (7 lb ft).  

Intermittents 

Faulty electrical connections or wiring may be the cause of intermittent conditions. Refer to Testing for 
Intermittent Conditions and Poor Connections in Wiring Systems. 

Symptom List 

Refer to a symptom diagnostic procedure from the following list in order to diagnose a symptom that does not 
set a DTC: 

z

Horns Always On  

z

Horns Inoperative  

z

Horns Inoperative - One Horn  

z

Horns - Poor Tone  

HORNS ALWAYS ON 

Test Description 

NOTE:

Refer to Fastener Notice in Cautions and Notices.

 

2004 Hummer H2 

2004 ACCESSORIES & EQUIPMENT Horns - Hummer H2

  

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

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

5: The horn relay control circuit includes the horn switch. The horn switch must be tested for a short to 
ground when testing the relay control circuit.  

Horns Always On 

Step

Action

Yes

No

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 body control module 

Horn Output ON and OFF.  

Are the horns on at all times?

Go to 

Step 3

Go to Testing for 

Intermittent Conditions 

and Poor Connections in 

Wiring Systems

3

1. Turn OFF the ignition.  

2. Disconnect the horn relay.  

Are the horns on at all times?

Go to 

Step 8

Go to Step 4

4

Connect a test lamp between the battery positive voltage 
circuit of the horn relay coil and the horn relay control 
circuit. 
Does the test lamp illuminate?

Go to 

Step 5

Go to Step 6

5

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

IMPORTANT:

The horn switch is part of the inflatable restraint steering 
wheel module. Refer to Inflatable Restraint Steering 
Wheel Module Replacement in SIR. To disable the SIR 
system, refer to SIR Disabling and Enabling Zone 3 in 
SIR.

Go to 

Step 11

Go to Step 7

6

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 11

Go to Step 9

7

Inspect for poor connections at the body control module. 
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 11

Go to Step 10

Repair the short to voltage in the horn control circuit. Refer 

 

2004 Hummer H2 

2004 ACCESSORIES & EQUIPMENT Horns - Hummer H2

  

HORNS INOPERATIVE 

Test Description 

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

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

5: Tests for voltage at the battery positive voltage terminal of the horn relay coil.  

7: Tests for voltage at the battery positive voltage terminal of the horn relay switch. The HORN fuse 
supplies power to the battery positive voltage terminal of the horn relay switch.  

13: The horns need maximum current flow to operate properly. A high resistance (greater than 0.5 ohm) 
in the horn control circuit or the horn ground circuit could cause operating problems with the horns. 
Inspect the circuits for faults that would restrict current flow.  

15: The horn relay control circuit includes the horn switch. The horn switch must be tested for a high 
resistance, an open or a short to voltage when testing the relay control circuit.  

Horns Inoperative 

8

to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you complete the repair?

Go to 

Step 11

-

9

Replace the horn relay. 
Did you complete the replacement?

Go to 

Step 11

-

10

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 11

-

11

Operate the horn. 
Do the horns operate properly?

System 

OK

Go to Step 1

Step

Action

Yes

No

1

Did you perform the Horns Diagnostic System 
Check?

Go to Step 2

Go to 

Diagnostic 

System Check -

Horns

2

Depress the horn switch. 
Do the horns operate?

Go to Step 3

Go to Step 5

3

1. Install a scan tool.  

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

3. With a scan tool, command the body control 

module (BCM) Horn Output ON and OFF.  

Go to Testing for 

Intermittent Conditions 

and Poor Connections in 

 

2004 Hummer H2 

2004 ACCESSORIES & EQUIPMENT Horns - Hummer H2

  

Do the horns operate?

Wiring Systems

Go to Step 4

4

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

Go to Step 21

Go to Step 11

5

1. Turn OFF the ignition.  

2. Disconnect the horn relay.  

3. 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 6

Go to Step 14

6

1. Connect a test lamp between the battery 

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

2. Depress and hold the horn switch.  

Does the test lamp illuminate?

Go to Step 7

Go to Step 15

7

Connect a test lamp between the battery positive 
voltage circuit of the horn relay switch and a good 
ground. 
Does the test lamp illuminate?

Go to Step 8

Go to Step 16

8

Momentarily connect a 15 amp fused jumper wire 
between the battery positive voltage circuit of the 
horn relay switch and the horn control circuit. 
Do the horns operate?

Go to Step 12

Go to Step 9

9

1. Reconnect the horn relay.  

2. Disconnect either horn connector.  

3. Connect a test lamp between the horn control 

circuit and a good ground.  

4. Depress and hold the horn switch.  

Does the test lamp illuminate?

Go to Step 10

Go to Step 17

10

1. Connect a test lamp between the horn control 

circuit and the horn ground circuit.  

2. Depress and hold the horn switch.  

Does the test lamp illuminate?

Go to Step 13

Go to Step 18

11

Inspect for poor connections at the harness connector 
of the 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 21

Go to Step 19

 

2004 Hummer H2 

2004 ACCESSORIES & EQUIPMENT Horns - Hummer H2