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

 

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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

 

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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

 

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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.

 

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