Hummer H2. Manual - part 1598

scan tool?

Aids

Go to Step 3

3

Command the fuel pump relay ON and OFF with a scan tool. 
Does the fuel pump relay turn ON and OFF when commanded 
with a scan tool?

Go to Step 9

Go to Step 4

4

1. Turn OFF the ignition.  

2. Remove the fuel pump relay.  

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

4. Probe the control circuit of the fuel pump relay with a 

test lamp that is connected to a good ground. Refer to 
Probing Electrical Connectors in Wiring Systems.  

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

tool.  

Does the test lamp turn ON and OFF when commanded with a 
scan tool?

Go to Step 5

Go to Step 6

5

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

fuel pump relay and the ground circuit of the fuel pump 
relay.  

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

tool.  

Does the test lamp turn ON and OFF when commanded with a 
scan tool?

Go to Step 

19

Go to Step 22

6

Does the test lamp remain illuminated?

Go to Step 7

Go to Step 8

7

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

Go to Step 

28

Go to Step 27

8

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

Go to Step 

28

Go to Step 20

9

Turn ON the ignition, with the engine OFF. 
Does the fuel pump operate continuously?

Go to Step 

10

Go to Step 11

10

1. Turn OFF the ignition.  

2. Remove the fuel pump relay.  

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

Does the fuel pump operate continuously?

Go to Step 

21

Go to Step 26

11

Inspect the fuel pump fuse. 
Is the fuel pump fuse open?

Go to Step 

12

Go to Step 14

1. Test the supply voltage circuit of the fuel pump, between 

 

2004 Hummer H2 

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

  

12

the fuel pump fuse and the fuel pump for a short to 
ground. Refer to Circuit Testing and Wiring Repairs in 
Wiring Systems.  

2. Replace the fuel pump fuse if necessary.  

Did you find and correct the condition?

Go to Step 

28

Go to Step 13

13

1. Install all removed electrical components.  

2. Install a new fuel pump fuse.  

3. Command the fuel pump relay ON with a scan tool.  

4. Inspect the fuel pump fuse.  

Is the fuel pump fuse open?

Go to Step 

24

Go to Intermittent 

Conditions

14

1. Turn OFF the ignition.  

2. Remove the fuel pump relay.  

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

4. Probe the battery voltage circuit of the fuel pump relay 

switch with a test lamp that is connected to a good 
ground.  

Does the test lamp illuminate?

Go to Step 

15

Go to Step 23

15

Connect a 20-amp fused jumper wire between the battery 
voltage circuit of the fuel pump relay switch and the supply 
voltage circuit of the fuel pump. 
Does the fuel pump operate?

Go to Step 

19

Go to Step 16

16

Test the supply voltage circuit of the fuel pump, between the 
fuel pump relay and the fuel pump for an open or for high 
resistance. Refer to Circuit Testing and Wiring Repairs in 
Wiring Systems. 
Did you find and correct the condition?

Go to Step 

28

Go to Step 17

17

Test the ground circuit of the fuel pump for an open or for high 
resistance. Refer to Circuit Testing and Wiring Repairs in 
Wiring Systems.Did you find and correct the condition?

IMPORTANT:

Inspect the ground circuit for being tight, corrosion on 
terminals, or damage to the wiring harness.

Go to Step 

28

Go to Step 18

18

Test for an intermittent or for a poor connection at the fuel 
pump sender assembly connector. 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 

28

Go to Step 24

19

Test for an intermittent or for a poor connection at the fuel 
pump relay. Refer to Testing for Intermittent Conditions and 

 

2004 Hummer H2 

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

  

FUEL SYSTEM DIAGNOSIS 

System Description 

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. 

The Fuel System is a returnless on-demand design. The fuel pressure regulator is a part of the fuel sender 

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

Go to Step 

28

Go to Step 26

20

Test for an intermittent and for a poor connection at the harness 
connector of the powertrain control module (PCM). 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 

28

Go to Step 27

21

Repair the short to voltage in the supply voltage circuit of the 
fuel pump. Refer to Wiring Repairs in Wiring Systems. 
Did you complete the repair?

Go to Step 

28

-

22

Repair the open in the fuel pump relay ground circuit. Refer to 
Wiring Repairs in Wiring Systems. 
Did you complete the repair?

Go to Step 

28

-

23

Repair the open in the battery voltage circuit of the fuel pump 
relay. Refer to Wiring Repairs in Wiring Systems. 
Did you complete the repair?

Go to Step 

28

-

24

Test for an intermittent and for a poor connection at the fuel 
pump sender assembly connector within the fuel tank. Refer to 
Testing for Intermittent Conditions and Poor Connections 
and Connector Repairs in Wiring Systems. 
Did you find and correct the conditions?

Go to Step 

28

Go to Step 25

25

1. Replace the fuel pump sender assembly. Refer to Fuel 

Sender Assembly Replacement .  

2. Replace the fuel pump fuse if necessary.  

Did you complete the replacement?

Go to Step 

28

-

26

Replace the fuel pump relay. 
Did you complete the replacement?

Go to Step 

28

-

27

Replace the PCM. Refer to Powertrain Control Module 
(PCM) Replacement . 
Did you complete the replacement?

Go to Step 

28

-

28

Operate the system in order to verify the repair. 
Did you correct the condition?

System OK

Go to Step 2

 

2004 Hummer H2 

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

  

assembly, eliminating the need for a return pipe from the engine. A returnless fuel system reduces the internal 
temperature of the fuel tank by not returning hot fuel from the engine to the fuel tank. Reducing the internal 
temperature of the fuel tank results in lower evaporative emissions. 

The fuel tank stores the fuel supply. An electric turbine style fuel pump attaches to the fuel sender assembly 
inside the fuel tank. The fuel pump supplies high pressure fuel through the fuel filter and the fuel feed pipe to 
the fuel injection system. The fuel pump provides fuel at a higher rate of flow than is needed by the fuel 
injection system. The fuel pump also supplies fuel to a venturi pump located on the bottom of the fuel sender 
assembly. The function of the venturi pump is to fill the fuel sender assembly reservoir. The fuel pressure 
regulator, a part of the fuel sender assembly, maintains the correct fuel pressure to the fuel injection system. The 
fuel pump and sender assembly contains a reverse flow check valve. The check valve and the fuel pressure 
regulator maintain fuel pressure in the fuel feed pipe and the fuel rail in order to prevent long cranking times. 

Fuel System Diagnosis 

Step

Action

Values

Yes

No

Schematic Reference: Fuel Hose/Pipes Routing Diagram (Single Fuel Tank)

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 with a scan tool.  

Does the fuel pump operate?

IMPORTANT:

Inspect the fuel system for external leaks before 
proceeding with this diagnostic.

-

Go to 

Step 3

Go to Fuel 

Pump 

Electrical 

Circuit 

Diagnosis

3

1. Turn OFF the ignition.  

2. Turn OFF all accessories. 

3. Install a fuel pressure gauge. Refer to Fuel Pressure 

IMPORTANT:

Verify that adequate fuel is in the fuel tank before 
proceeding with this diagnostic.

CAUTION:

Wrap a shop towel around the fuel pressure 
connection in order to reduce the risk of fire and 
personal injury. The towel will absorb any fuel 
leakage that occurs during the connection of the fuel 
pressure gauge. Place the towel in an approved 
container when the connection of the fuel pressure 
gauge is complete.

385-425 

kPa (55-

62 psi) 

VIN Z : 

 

2004 Hummer H2 

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