Hummer H2. Manual - part 1381

Fig. 2: RR Of Engine Compartment Component Views 
Courtesy of GENERAL MOTORS CORP. 

Callouts For Fig. 2 

COOLING SYSTEM CONNECTOR END VIEWS 

Coolant Level Terminal Identification Switch (If Equipped) 

Callout

Component Name

1

A/C Low Pressure Switch

2

A/C Accumulator

3

Intake Air Temperature (IAT)/Mass Air Flow (MAF) Sensor

4

Coolant Level Switch (If Equipped)

 

2004 Hummer H2 

2004 ENGINE Engine Cooling - Hummer H2

  

DIAGNOSTIC INFORMATION AND PROCEDURES 

DIAGNOSTIC STARTING POINT - ENGINE COOLING 

Begin the system diagnosis with the Diagnostic System Check - Engine Cooling . The Diagnostic System 
Check will provide the following information: 

z

The identification of the control module(s) which command the system.  

z

The ability of the control module(s) to communicate through the serial data circuit.  

z

The identification of any stored diagnostic trouble codes (DTCs) and their status.  

The use of the Diagnostic System Check will identify the correct procedure for diagnosing the system and 
where the procedure is located. 

DIAGNOSTIC SYSTEM CHECK - ENGINE COOLING 

Test Description 

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

3: Lack of communication may be due to a partial malfunction of the class 2 serial data circuit or due to a 
total malfunction of the class 2 serial data circuit. The specified procedure will determine the particular 
condition.  

Connector Part Information

z

12052644  

z

2-Way F Metri-Pack 150 Series Sealed (GY)  

Pin

Wire Color

Circuit No.

Function

A

L-GN

1478

Coolant Level Switch Signal

B

BK

550

Ground

 

2004 Hummer H2 

2004 ENGINE Engine Cooling - Hummer H2

  

4: Determine if the Instrument Cluster or Powertrain Control Modules have set DTCs which may affect 
Engine Cooling operation are present.  

5: The presence of DTCs which begin with "U" indicate some other module is not communicating. The 
specified procedure will compile all the available information before tests are performed.  

Diagnostic System Check - Engine Cooling 

SCAN TOOL OUTPUT CONTROLS 

Instrument Cluster 

Step

Action

Yes

No

1

Did you review a Diagnostic 
Starting Point-Engine Cooling?

Go to Step 2

Go to Diagnostic Starting 

Point - Engine Cooling

2

Install a scan tool. 
Does the scan tool power up?

Go to Step 3

Go to Scan Tool Does Not 

Power Up in Data Link 

Communications

3

1. Turn ON the ignition, with 

the engine OFF.  

2. Attempt to establish 

communication with the 
following control modules: 

z

The instrument cluster  

z

The powertrain control 
module  

Does the scan tool communicate 
with the control modules?

Go to Step 4

Go to Scan Tool Does Not 

Communicate with Class 2 

Device in Data Link 

Communications

4

Select the powertrain control 
module display DTCs function on 
the scan tool. 
Does the scan tool display any 
DTCs?

Go to Step 5

Go to Symptoms - Engine 

Cooling

5

Does the scan tool display any 
DTCs which begin with a "U"?

Go to Scan Tool Does Not 

Communicate with Class 2 

Device in Data Link 

Communications

Go to Step 6

6

Does the scan tool display any 
DTCs that are associated with the 
Engine Cooling System?

Go to Diagnostic Trouble 

Code (DTC) List

Go to Diagnostic Trouble 

Code (DTC) List in Engine 

Controls - 4.8L, 5.3L, and 6.0L

Scan Tool Output 

Control

Additional Menu 

Selection(s)

Description

Special Functions

Lamp Test

Command the instrument cluster to illuminate all 
lamps in the cluster

Special Functions

IPC Gauges

Command the instrument cluster to sweep all gauges.

 

2004 Hummer H2 

2004 ENGINE Engine Cooling - Hummer H2

  

SCAN TOOL DATA LIST 

Instrument Panel Cluster (IPC) 

6.0L 

SCAN TOOL DATA DEFINITIONS 

Coolant Level Switch - Range: Low/OK  

This parameter indicates when the engine coolant level is low. The scan tool displays Low when the 
powertrain control module (PCM) detects the engine coolant level switch is open. 

ECT - Range: -40° C to +150° C (-40° F to +302° F)  

The PCM applies 5.0 volts to the ECT sensor circuit. The sensor is a thermistor which changes internal 
resistance as the engine temperature changes. When the sensor is cold (internal resistance high), the PCM 
senses a high signal voltage and interprets the voltage as a cold engine. As the sensor warms (internal 
resistance decreases), the voltage signal decreases and the PCM interprets the lower voltage as a warm 
engine. 

Displayed Coolant Temperature - Range: 32-127° C (89-260° F)  

This data is the coolant temperature the Instrument Cluster is attempting to display on the coolant 
temperature gauge. This data may differ from the monitored coolant temperature for a period of time due 
to filtering. The data may also differ from the monitored coolant temperature when coolant temperature is 
not in the range of 71-127° C (160-260° F) since the display is limited to these values. If a class 2 
communication failure occurs, this data will be at the minimum value of 32° C (89° F). 

Special Functions

Segment Tests

Command the instrument cluster message center to 
display all segments.

Scan Tool 

Parameter

Data 

List

Units Displayed

Typical Data Value

Ignition Switch in RUN/Engine running/Automatic Transmission in PARK/Manual Transmission 

in NEUTRAL/Air Conditioner is OFF

Displayed Coolant 

Temp

Data

Celsius (C)/Fahrenheit 

(F)

87° C (189° F)

Monitored Coolant 

Temp

Data

Celsius (C)/Fahrenheit 

(F)

87° C (Fluctuates range 82-93° C) 189° F 

(Fluctuates range 180-200° F)

Scan Tool Parameter

Data List

Units Displayed

Typical Data Value

Ignition Switch in RUN/Engine running/Automatic Transmission in PARK/Manual Transmission 

in NEUTRAL/Air Conditioner is OFF

ECT Sensor

Engine Data 1 
Engine Data 2

Degrees

87° C (189° F)

Coolant Level Switch

Engine Data 2

Low/OK

OK

 

2004 Hummer H2 

2004 ENGINE Engine Cooling - Hummer H2