Hummer H2. Manual - part 309

When the body control module (BCM) receives a signal requesting to illuminate the backup lamps, battery 
voltage is sent directly from the BCM through the backup lamp supply voltage circuit to the backup lamps. 

Voltage for the backup lamp supply voltage circuit as well as the courtesy lamp supply voltage circuit is from 
the left instrument panel fuse block TBC 2B 15-amp fuse directly through the BCM to these circuits. 

Conditions for Running the DTC 

The battery voltage must be between 9.0-16.0 volts. 

Conditions for Setting the DTC 

z

When the BCM receives a backup lamp request signal and the backup lamp supply voltage circuit is 
shorted to ground.  

z

When the BCM is not receiving a backup lamp request signal and the backup lamp supply voltage circuit 
is open or shorted to voltage.  

z

There is a loss of the instrument panel fuse block TBC 2B battery supply voltage to the BCM for 1 
second.  

Action Taken When the DTC Sets 

The backup lamps will not operate. 

Conditions for Clearing the MIL/DTC 

z

This DTC will clear on current status after the condition for setting the fault is corrected.  

z

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

z

History and current DTCs can be cleared using a scan tool.  

Diagnostic Aids 

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.  

z

A short to ground on the backup lamp supply voltage circuit, courtesy lamp supply voltage circuit OR the 
TBC 2B battery positive voltage circuit to the BCM will open the TBC 2B fuse in the left instrument 
panel fuse block.  

Test Description 

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

3: This step test determines if the problem exists in the wiring or the BCM.  

4: This step test determines if the problem exists in the wiring or the BCM.  

5: After replacement of the BCM you must calibrate the new module for proper operation. 

 

2004 Hummer H2 

2004 ACCESSORIES & EQUIPMENT Lighting Systems - Hummer H2

  

DTC B2550 

DTC B2575 

Step

Action

Yes

No

Schematic Reference: Exterior Lights Schematics . 
Connector End View Reference: Lighting Systems Connector End Views or Body Control System 
Connector End Views in Body Control System.

1

Did you perform the Lighting System Diagnostic System 
Check?

Go to 

Step 2

Go to Diagnostic System 

Check - Lighting Systems

2

Inspect the TBC 2B fuse in the instrument panel fuse block. 
Is the fuse open?

Go to 

Step 3

Go to Step 4

3

Test the following circuits for a short to ground. Refer to 
Circuit Testing and Wiring Repairs in Wiring Systems: 

z

Backup lamp supply voltage  

z

Courtesy lamp supply voltage  

z

TBC 2B battery positive voltage to the body control 
module (BCM)  

 
Did you find and correct the condition?

Go to 

Step 6

Go to Step 5

4

Test the backup lamp supply voltage circuit for the following 
conditions: 

z

An open  

z

A short to voltage  

z

High resistance 

Refer to Circuit Testing and Wiring Repairs in 
Wiring Systems. 

 
Did you find and correct the condition?

Go to 

Step 6

Go to Step 5

5

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

IMPORTANT:

Perform the setup procedure for the BCM.

Go to 

Step 6

-

6

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

 

2004 Hummer H2 

2004 ACCESSORIES & EQUIPMENT Lighting Systems - Hummer H2

  

Circuit Description 

When the body control module (BCM) senses a request for low beam headlamp illumination, the BCM sends a 
ground signal to the low beam headlamp relay through the headlamp low beam relay control circuit. The 
headlamp low beam relay will apply voltage to illuminate the headlamps. 

Conditions for Running the DTC 

The battery voltage must be between 9.0-16.0 volts. 

Conditions for Setting the DTC 

z

When the BCM receives a command to illuminate the low beam headlamps and the headlamp low beam 
relay control circuit is open or shorted to voltage.  

z

When the BCM does not receive a command to illuminate the low beam headlamps and the headlamp 
low beam relay control circuit is shorted to ground.  

z

When the low beam relay coil side is open or the battery positive voltage to the low beam relay is open.  

Action Taken When the DTC Sets 

The low beam headlamps will not operate or will remain always on. 

Conditions for Clearing the MIL/DTC 

z

This DTC will clear on current status after the condition for setting the fault is corrected.  

z

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

z

History and current DTC(s) can be cleared using a scan tool.  

Test Description 

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

3: Tests for voltage at the voltage supply side of the headlamp low beam relay.  

4: Verifies that the BCM is providing ground to the headlamp low beam relay.  

5: Tests if ground is constantly being applied to the headlamp low beam relay.  

6: Tests if there is opposing voltage present or an open headlamp low beam relay control circuit, 
including the relay coil side.  

12: After replacement of the BCM you must calibrate the new module for proper operation.  

DTC B2575 

Step

Action

Yes

No

Schematic Reference: Headlights/Daytime Running Lights (DRL) Schematics 
Connector End View Reference: Lighting Systems Connector End Views or Body Control System 
Connector End Views in Body Control System

Did you perform the Lighting Systems 

Go to Diagnostic 

 

2004 Hummer H2 

2004 ACCESSORIES & EQUIPMENT Lighting Systems - Hummer H2

  

1

Diagnostic System Check?

Go to Step 2

System Check - 

Lighting Systems

2

1. Turn ON the ignition, with the engine 

OFF.  

2. Place the headlamp switch in the ON 

position.  

3. Place the headlamp dimmer switch in the 

low beam position.  

4. Place the headlamp switch in the OFF 

position.  

Do the low beam headlamps operate as 
expected?

Go to Testing for 

Intermittent Conditions 

and Poor Connections in 

Wiring Systems

Go to Step 3

3

1. Turn OFF the ignition.  

2. Disconnect the headlamp low beam relay.  

3. Turn ON the ignition, with the engine 

OFF.  

4. Connect a test lamp between the control 

circuit of the headlamp low beam relay 
and a good ground.  

Does the test lamp illuminate?

Go to Step 4

Go to Step 10

4

1. Connect a test lamp between the control 

circuit of the headlamp low beam relay 
and the battery positive voltage circuit of 
the headlamp low beam relay.  

2. While observing the test lamp, place the 

headlamp switch in the ON position, and 
then the OFF position.  

Does the test lamp turn ON and OFF with each 
cycle of the switch?

Go to Step 8

Go to Step 5

5

Does the test lamp remain illuminated with each 
cycle of the switch?

Go to Step 7

Go to Step 6

6

Test the control circuit of the headlamp low 
beam relay for a short to voltage or 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 headlamp low 
beam relay for a short to ground. Refer to 
Circuit Testing and Wiring Repairs in Wiring 
Systems. 

 

2004 Hummer H2 

2004 ACCESSORIES & EQUIPMENT Lighting Systems - Hummer H2