Hummer H2. Manual - part 1597

Repairs in Wiring Systems. 
Did you find and correct the condition?

Go to Step 30

Go to Step 15

15

Test the battery positive voltage bus bar circuit of the 
underhood junction block between the 40-amp IGN B fuse 
and the ignition switch for a short to ground. 
Did you find a condition?

Go to Step 29

Go to Step 16

16

Test the ignition 1 voltage bus bar circuit of the underhood 
junction block that contains the ignition relay for a short to 
ground. 
Did you find a condition?

Go to Step 29

Go to Step 27

17

1. Turn OFF the ignition.  

2. Probe the mounting stud for the battery positive cable 

at the underhood junction block with a test lamp that 
is connected to a good ground. Refer to Probing 
Electrical Connectors and Troubleshooting with a 
Test Lamp in Wiring Systems.  

Does the test lamp illuminate?

Go to Step 29

Go to Diagnostic 

System Check - 

Engine Electrical 

in Engine 
Electrical

18

1. Turn OFF the ignition.  

2. Remove the ignition relay with the J 43244 from the 

underhood junction block. Refer to Relay 
Replacement (Within an Electrical Center) or 
Relay Replacement (Attached to Wire Harness) in 
Wiring Systems. 

3. Probe the battery positive voltage circuit of the 

ignition relay at the underhood junction block with a 
test lamp that is connected to a good ground. Refer to 
Probing Electrical Connectors and 
Troubleshooting with a Test Lamp in Wiring 
Systems.  

Does the test lamp illuminate?

NOTE:

Refer to Test Probe Notice in Cautions and 
Notices.

Go to Step 19

Go to Step 29

19

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

2. Probe the ignition 1 voltage circuit of the ignition 

relay at the underhood junction block with a test 
lamp that is connected to a good ground. Refer to 
Probing Electrical Connectors and 
Troubleshooting with a Test Lamp in Wiring 
Systems.  

 

2004 Hummer H2 

2004 ENGINE PERFORMANCE Engine Controls (Troubleshooting) - 4.8L, 5.3L, and 6.0L - Hummer H2

  

Does the test lamp illuminate?

Go to Step 23

Go to Step 20

20

1. Turn OFF the ignition.  

2. Test the ignition 1 voltage circuit between the 

ignition switch and the underhood junction block for 
a high resistance or for an open. Refer to Circuit 
Testing and Wiring Repairs in Wiring Systems.  

Did you find and correct the condition?

Go to Step 30

Go to Step 21

21

Test the ignition switch assembly for a high resistance or 
for an open. Refer to Circuit Testing in Wiring Systems. 
Did you find a condition?

Go to Step 28

Go to Step 22

22

Test the battery positive voltage circuit between the 
ignition switch and the underhood junction block for a high 
resistance or for an open. Refer to Circuit Testing and 
Wiring Repairs in Wiring Systems. 
Did you find and correct the condition?

Go to Step 30

Go to Step 29

23

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

2. Probe the coil ground circuit of the ignition relay at 

the underhood junction block with a test lamp that is 
connected to battery voltage. Refer to Probing 
Electrical Connectors and Troubleshooting with a 
Test Lamp in Wiring Systems.  

Does the test lamp illuminate?

Go to Step 25

Go to Step 24

24

1. Turn OFF the ignition.  

2. Disconnect the negative battery cable at the battery. 

Refer to Battery Negative Cable 
Disconnect/Connect Procedure (Single Battery) in 
Engine Electrical.  

3. Disconnect the underhood junction block electrical 

connectors.  

4. Test the coil ground circuit of the ignition relay at the 

underhood junction block electrical connector for a 
high resistance or for an open. Refer to Circuit 
Testing and Wiring Repairs in Wiring Systems.  

Did you find and correct the condition?

Go to Step 30

Go to Step 29

1. Turn OFF the ignition.  

2. Jumper the ignition relay battery positive voltage 

circuit and the ignition relay load circuit together at 
the underhood junction block with a 20-amp fused 
jumper wire. Refer to Using Fused Jumper Wires in 
Wiring Systems.  

 

2004 Hummer H2 

2004 ENGINE PERFORMANCE Engine Controls (Troubleshooting) - 4.8L, 5.3L, and 6.0L - Hummer H2

  

FUEL PUMP ELECTRICAL CIRCUIT DIAGNOSIS 

Circuit Description 

25

3. Probe the following fuses with a test lamp that is 

connected to a good ground: 

z

PCM 1  

z

ETC/ECM  

z

INJ 1  

z

INJ 2  

z

SBA, if equipped. 

Refer to Probing Electrical Connectors and 
Troubleshooting with a Test Lamp in Wiring 
Systems. 

Does the test lamp illuminate on at least one test point of 
each fuse?

Go to Step 26

Go to Step 29

26

Test for an intermittent and for a poor connection at the 
underhood junction block, ignition relay connector 
location. Refer to Testing for Intermittent Conditions 
and Poor Connections in Wiring Systems. 
Did you find a condition?

Go to Step 29

Go to Step 27

27

Replace the ignition relay. Refer to Relay Replacement 
(Within an Electrical Center) or Relay Replacement 
(Attached to Wire Harness) in Wiring Systems. 
Did you complete the replacement?

Go to Step 30

-

28

Replace the ignition switch. Refer to Ignition Switch 
Replacement in Steering Wheel and Column. 
Did you complete the replacement?

Go to Step 30

-

29

Replace the underhood electrical center. Refer to 
Underhood Electrical Center or Junction Block 
Replacement in Wiring Systems. 
Did you complete the replacement?

Go to Step 30

-

30

1. Replace any open fuses.  

2. Turn OFF the ignition for 30 seconds.  

3. Attempt to start the engine.  

Does the engine start and run?

Go to Step 31

Go to Engine 

Cranks but Does 

Not Run

31

1. Clear the DTCs with a scan tool.  

2. Operate the vehicle for 5 minutes.  

Does a DTC set during this ignition cycle?

Go to Diagnostic 

Trouble Code 

(DTC) List

System OK

 

2004 Hummer H2 

2004 ENGINE PERFORMANCE Engine Controls (Troubleshooting) - 4.8L, 5.3L, and 6.0L - Hummer H2

  

The control module enables the fuel pump relay when the ignition switch is turned ON. The control module will 
disable the fuel pump relay within two seconds unless the control module detects ignition reference pulses. The 
control module continues to enable the fuel pump relay as long as ignition reference pulses are detected. The 
control module disables the fuel pump relay within two seconds if ignition reference pulses cease to be detected 
and the ignition remains ON. 

Diagnostic Aids 

A fuel pump prime terminal is located at the underhood bussed electrical center (UBEC). Refer to the UBEC 
cover for terminal location. 

The following conditions may have caused the fuel pump fuse to open: 

z

A faulty fuse  

z

An intermittent short in the fuel pump power supply circuit  

z

An intermittent internal component failure  

For an intermittent condition, refer to Intermittent Conditions . 

Test Description 

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

3: This step determines if the condition is located on the coil side or on the switch side of the fuel pump 
relay.  

4: This step verifies that the powertrain control module (PCM) is providing voltage to the fuel pump 
relay.  

5: This step tests for an open in the ground circuit to the fuel pump relay.  

6: This step determines if a voltage is constantly being applied to the fuel pump relay.  

13: This step determines if the condition with the circuit is intermittent.  

Fuel Pump Electrical Circuit Diagnosis 

Step

Action

Yes

No

Schematic Reference: Engine Controls Schematics 
Connector End View Reference: Engine Controls Connector End Views or Powertrain Control 
Module (PCM) Connector End Views

1

Did you perform the Diagnostic System Check - Engine 
Controls?

Go to Step 2

Go to Diagnostic 

System Check - 

Engine Controls

2

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

2. Command the fuel pump relay ON and OFF with a scan 

tool.  

Does the fuel pump turn ON and OFF when commanded with a 

Go to 

Diagnostic 

 

2004 Hummer H2 

2004 ENGINE PERFORMANCE Engine Controls (Troubleshooting) - 4.8L, 5.3L, and 6.0L - Hummer H2