Hummer H2. Manual - part 1596

IGNITION RELAY DIAGNOSIS 

Circuit Description 

The ignition relay is a normally open relay. The relay armature is held in the open position by spring tension. 
When the ignition switch is turned to the run or start position, current will flow through the relay coil. A wire 
connected to the other end of the relay coil completes the path to ground. The electromagnetic field created by 
the relay coil, overcomes the spring tension and moves the armature allowing the relay contacts to close. The 
closed relay contacts allow current to flow from the battery to the following fuses: 

z

PCM 1  

z

ETC/ECM  

z

INJ 1  

z

INJ 2  

z

SBA, if equipped.  

When the ignition switch is turned to the OFF position, the electromagnetic field collapses. This action allows 
the spring tension to move the armature away from the relay contacts, which interrupts current flow to the fuses.

If the ignition relay fails to close, the engine will crank, but will not run. The class 2 communications will be 
available with the use of a scan tool. 

The ignition relay table assumes that the vehicle battery is fully charged. Refer to Battery Inspection/Test 
(Non-HP2) in Engine Electrical. 

Ignition Relay Diagnosis 

Did you complete the replacement?

Go to Step 13

-

13

1. Clear the DTCs with a scan tool.  

2. Turn OFF the ignition for 30 seconds.  

3. Attempt to start the engine.  

Does the engine start the continue to run?

-

Go to Step 14

Go to Step 2

14

1. Allow the engine to reach operating 

temperature.  

2. Observe the DTC information with a scan 

tool.  

Are there any DTCs that have not been diagnosed?

-

Go to 

Diagnostic 

Trouble Code 

(DTC) List

System OK

Step

Action

Yes

No

Schematic Reference: Power Distribution Schematics and Ground Distribution Schematics in 
Wiring Systems and Engine Controls Schematics 
Connector End View Reference: Engine Controls Connector End Views or Powertrain Control 

 

2004 Hummer H2 

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

  

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. Remove the underhood junction block cover.  

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 3

Go to Step 10

3

1. Turn OFF the ignition.  

2. Probe both test points of the PCM 1 fuse 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 on either test point of the 
fuse?

Go to Step 4

Go to Step 30

4

1. Turn OFF the ignition.  

2. Remove the ignition relay from the underhood 

junction block with the J 43244 Relay Puller Pliers. 
Refer to Relay Replacement (Within an Electrical 
Center) or Relay Replacement (Attached to Wire 
Harness) in Wiring Systems. 

3. 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 

NOTE:

Refer to Test Probe Notice in Cautions and 
Notices.

 

2004 Hummer H2 

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

  

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

Does the test lamp illuminate?

Go to Step 7

Go to Step 5

5

Test the relay load bus bar of the underhood junction block 
between the ignition relay and the fuses to the circuit 
components for a short to battery positive voltage. Refer to 
Circuit Testing in Wiring Systems. 
Did you find a condition?

Go to Step 29

Go to Step 6

6

1. Turn OFF the ignition.  

2. Remove the following fuses from the underhood 

junction block: 

z

PCM 1  

z

ETC/ECM  

z

INJ 1  

z

INJ 2  

z

SBA, if equipped.  

3. Probe the above fuse terminals in 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 at any of the fuse terminals?

Go to Diagnostic 

System Check - 

Engine Electrical 

in Engine 
Electrical

Go to Step 27

7

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 

connector that contains the ignition 1 voltage circuit 
for the ignition relay.  

4. Disconnect the ignition switch electrical connector 

that contains the ignition 1 voltage circuit for the 
ignition relay.  

5. Connect the negative battery cable to the battery.  

6. Test the ignition 1 voltage circuit for a short to 

battery positive voltage. Refer to Circuit Testing 
and Wiring Repairs in Wiring Systems.  

Did you find and correct the condition?

Go to Step 30

Go to Step 8

 

2004 Hummer H2 

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

  

8

1. Turn OFF the ignition.  

2. Probe the ignition 1 voltage terminal on the ignition 

switch side of the ignition switch electrical connector 
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 28

Go to Step 9

9

Test the ignition 1 voltage bus bar circuit in the underhood 
junction block for a short to battery positive voltage. Refer 
to Circuit Testing in Wiring Systems. 
Did you find a condition?

Go to Step 29

Go to Step 27

10

1. Turn OFF the ignition.  

2. Inspect the 40-amp IGN B fuse in the underhood 

junction block. Refer to Circuit Protection - Fuses 
in Wiring Systems.  

Is the fuse open?

Go to Step 11

Go to Step 18

11

1. Remove the 40-amp IGN B fuse from the underhood 

junction block. 

2. Probe both fuse terminals in 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 on at least one fuse terminal?

NOTE:

Refer to Test Probe Notice in Cautions and 
Notices.

Go to Step 12

Go to Step 17

12

Test the ignition 1 voltage circuit between the ignition 
switch and the underhood junction block 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 30

Go to Step 13

13

Test the ignition switch assembly for a short to ground. 
Refer to Circuit Testing in Wiring Systems. 
Did you find a condition?

Go to Step 28

Go to Step 14

14

Test the battery positive voltage circuit between the 
underhood junction block and the ignition switch for a 
short to ground. Refer to Circuit Testing and Wiring 

 

2004 Hummer H2 

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