Hummer H2. Manual - part 1383

ENGINE OVERHEATING 

Engine Overheating 

in the Engine Data 2 data list.  

Does the scan tool display OK?

Go to 

Step 10

Go to Step 6

6

Inspect the coolant level signal circuit for an open or short. 
Refer to Circuit Testing and Wiring Repairs in Wiring 
Systems. 
Did you find and correct the condition?

Go to 

Step 14

Go to Step 9

7

Inspect for poor connections at the harness connector of the 
IPC. 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 14

Go to Step 11

8

Inspect for poor connections at the harness connector of the 
coolant level sensor. 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 14

Go to Step 12

9

Inspect for poor connections 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 14

Go to Step 13

10

Repair the open in the ground circuit of the coolant level 
sensor. Refer to Wiring Repairs in Wiring Systems. 
Did you complete the repair?

Go to 

Step 14

-

11

Replace the IPC. Refer to Instrument Panel Cluster 
(IPC) Replacement in Instrument Panel, Gauges and 
Console. 
Did you complete the repair?

Go to 

Step 14

-

12

Replace the surge tank. Refer to Surge Tank 
Replacement . 
Did you complete the repair?

Go to 

Step 14

-

13

Replace the PCM. Refer to Powertrain Control Module 
(PCM) Replacement in Engine Controls. 
Did you complete the repair?

Go to 

Step 14

-

14

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

System 

OK

Go to Step 3

Step

Action

Yes

No

1

Inspect for a missing or damaged radiator side or upper baffle and/or radiator 
air deflector. 
Is the baffle and/or deflector missing or damaged?

Go to 

Step 8

Go to 

Step 2

 

2004 Hummer H2 

2004 ENGINE Engine Cooling - Hummer H2

  

2

Inspect for a loss of coolant. 
Is there a loss of coolant?

Go to 

Step 3

Go to 

Step 4

3

Fill the system to the specified level. 
Does the engine overheat?

Go to 

Step 4

System 

OK

4

Inspect for low temperature protection. 
Is the coolant to the correct concentration?

Go to 

Step 5

Go to 

Step 8

5

Inspect for a loss of cooling system pressure. 
Is there a loss of system pressure?

Go to 

Step 8

Go to 

Step 6

6

Inspect for a faulty engine coolant temperature (ECT) sensor. Refer to DTC 
P0117 and DTC P0118 in Engine Controls - 4.8L, 5.3L, and 6.0L. 
Is the sensor operating properly?

Go to 

Step 7

Go to 

Step 8

7

Inspect for the following: 

z

Damaged coolant surge tank  

z

Leaking hose  

z

Bad/Incorrect surge tank or radiator cap  

 
Were any of the above found?

Go to 

Step 8

Go to 

Step 10

8

Repair or install new parts as necessary, then retest. 
Does the engine overheat?

Go to 

Step 9

System 

OK

9

Inspect for incorrect drive belt tension. 
Is the belt tension correct?

Go to 

Step 10

Go to 

Step 8

10

1. Remove the water pump. Refer to Water Pump Replacement .  

2. Inspect for a damaged water pump shaft/hub.  

Is the water pump driveshaft damaged or is the seal leaking?

Go to 

Step 8

Go to 

Step 11

11

Inspect for obstructed radiator air flow or bent radiator fins. 
Is the radiator air flow obstructed?

Go to 

Step 8

Go to 

Step 12

12

Inspect for blocked cooling system passages. 
Are the cooling system passages blocked?

Go to 

Step 8

Go to 

Step 13

13

Inspect for inoperative fan clutch. Refer to Fan Clutch Diagnosis . 
Is the fan clutch operating correctly?

Go to 

Step 14

Go to 

Step 8

14

Inspect the thermostat. Refer to Thermostat Diagnosis . 
Is the thermostat stuck in the closed position?

Go to 

Step 15

Go to 

Step 16

15

Replace the thermostat. Refer to Thermostat Housing Replacement . 
Does the engine overheat?

Go to 

Step 16

System 

OK

16

Inspect the radiator cooling capacity. 
Is the proper sized radiator being used on the vehicle?

Go to 

Step 3

Go to 

Step 17

17

Consult the current parts catalog and replace the radiator. Refer to Radiator 
Replacement . 
Is the repair complete?

System 

OK

-

 

2004 Hummer H2 

2004 ENGINE Engine Cooling - Hummer H2

  

LOSS OF COOLANT 

Loss of Coolant 

Step

Action

Yes

No

DEFINITION: The cooling system is loosing coolant either internally or externally.

1

Were you sent here from Symptoms, or another diagnostic table?

Go to 

Step 2

Go to Symptoms - 

Engine Cooling

2

Repair any present DTCs. Refer to Diagnostic System Check - 
Engine Cooling . 
Is the action complete?

Go to 

Step 3

-

3

Inspect the coolant level. 
Is the coolant at the proper level?

Go to 

Step 5

Go to Step 4

4

Fill the cooling system to the proper level. Refer to Draining and 
Filling Cooling System . 
Is the action complete?

Go to 

Step 5

-

5

Engine overheating can cause a loss of coolant. 
Is the engine overheating?

Go to 

Step 19

Go to Step 6

6

1. Idle the engine at normal operating temperature.  

2. Inspect for heavy white smoke coming out of the exhaust 

pipe.  

Is a heavy white smoke present from the exhaust pipe?

Go to 

Step 7

Go to Step 8

7

Coolant in the exhaust system creates a distinctive, burning coolant 
odor in the exhaust. 
Condensation in the exhaust system can cause an odorless white 
smoke during engine warm up. 
Does the white smoke have a burning coolant type odor?

Go to 

Step 20

Go to Step 8

8

Visually inspect the hoses, pipes and hose clamps. 
Are any of the hoses, clamps or pipes leaking?

Go to 

Step 21

Go to Step 9

9

Visually inspect the following components: 

z

Block heater  

z

Coolant pressure cap  

z

Core plugs  

z

Throttle Body  

z

Engine block  

z

Intake manifold  

z

Radiator  

z

Thermostat housing  

z

Water pump  

 
Are any of the listed components leaking?

Go to 

Step 21

Go to Step 10

 

2004 Hummer H2 

2004 ENGINE Engine Cooling - Hummer H2

  

10

1. Pressure test the cooling system. Refer to Cooling System 

Leak Testing .  

2. With the cooling system pressurized, visually inspect the 

components listed in steps 7 and 8.  

Are any leaks present?

Go to 

Step 21

Go to Step 11

11

Pressure test the coolant pressure cap. Refer to Pressure Cap 
Testing . 
Does the coolant pressure cap hold pressure?

Go to 

Step 12

Go to Step 16

12

Inspect for the following conditions: 

z

A coolant smell inside of the vehicle  

z

Coolant in the HVAC module drain tube  

z

Coolant on the vehicle floor covering near the HVAC 
module  

 
Is coolant present?

Go to 

Step 21

Go to Step 13

13

Inspect the underside of the engine oil fill cap for a gray/white 
milky substance. 
Is there a milky substance under the oil fill cap?

Go to 

Step 14

Go to Step 15

14

Inspect the engine oil fluid level indicator for a gray/white milky 
substance. 
Is there a milky substance on the engine oil fluid level indicator?

Go to 

Step 17

Go to Step 15

15

Inspect the automatic transmission oil fluid level indicator, if 
equipped, for a gray/white milky substance. 
Is there a milky substance on the automatic transmission fluid level 
indicator?

Go to 

Step 18

Go to Step 22

16

Replace the coolant pressure cap. 
Is the repair complete?

Go to 

Step 22

-

17

1. Replace the radiator. Refer to Radiator Replacement .  

2. Service the engine oil and filter. Refer to Engine Oil and Oil 

Filter Replacement in Engine Mechanical - 4.8L, 5.3L, and 
6.0L.  

Is the repair complete?

Go to 

Step 22

-

18

1. Replace the radiator. Refer to Radiator Replacement .  

2. Service the automatic transmission. Refer to Engine 

Coolant/Water in Transmission in Automatic 
Transmission.  

Is the repair complete?

Go to 

Step 22

-

Repair the engine overheating condition. Refer to Engine 

 

2004 Hummer H2 

2004 ENGINE Engine Cooling - Hummer H2