Hummer H2. Manual — part 1484

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The mass air flow (MAF) sensor

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The intake air temperature (IAT) sensor

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The vehicle speed sensor (VSS)

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The transmission gear position or range information sensors

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The engine knock sensors (KS)

Modes of Operation

There is one normal mode of operation, with the spark under PCM control. If the CKP pulses are lost the engine
will not run. The loss of a CMP signal may result in a longer crank time since the PCM cannot determine which
stroke the pistons are on. Diagnostic trouble codes are available to accurately diagnose the ignition system with
a scan tool.

KNOCK SENSOR (KS) SYSTEM DESCRIPTION

Purpose

The knock sensor (KS) system enables the control module to control the ignition timing for the best possible
performance while protecting the engine from potentially damaging levels of detonation. The control module
uses the KS system to test for abnormal engine noise that may indicate detonation, also known as spark knock.

Sensor Description

This knock sensor (KS) system uses one or 2 broadband one-wire sensors. The sensor uses piezo-electric crystal
technology that produces an AC voltage signal of varying amplitude and frequency based on the engine
vibration, or noise, level. The amplitude and frequency are dependant upon the level of knock that the KS
detects. The control module receives the KS signal through a signal circuit. The KS ground is supplied by the
engine block through the sensor housing.

One way the control module monitors the system is by output of a bias voltage on the KS signal wire. The bias
voltage creates a voltage drop that the control module monitors and uses to help diagnose KS faults. The KS
noise signal rides along this bias voltage, and due to the constantly fluctuating frequency and amplitude of the
signal, will always be outside of the bias voltage parameters.

Another way the control module monitors the system is by learning the average normal noise output from the
KS. The control module learns a minimum noise level, or background noise, at idle from the KS and uses
calibrated values for the rest of the RPM range. The control module uses the minimum noise level to calculate a
noise channel. The control module uses this noise channel, and the KS signal that rides along the noise channel,
in much the same way as the bias voltage type does. As engine speed and load change, the noise channel upper
and lower parameters will change to accommodate the normal KS signal.

In order to determine which cylinders are knocking, the control module only uses KS signal information when
each cylinder is near top dead center (TDC) of the firing stroke. If the control module has determined that knock
is present, it will retard the ignition timing to attempt to eliminate the knock. The control module will always try
to work back to a zero compensation level, or no spark retard. An abnormal KS signal will fall within the noise
channel or will not be present. KS diagnostics are calibrated to detect faults with the KS circuitry inside the

2004 Hummer H2

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

control module, the KS wiring, or the KS voltage output.

AIR INTAKE SYSTEM DESCRIPTION

The primary function of the air intake system is to provide filtered air to the engine. The system uses a cleaner
element mounted in a housing. The cleaner housing is remotely mounted and uses intake ducts to route the
incoming air into the throttle body. The secondary function of the air intake system is to muffle air induction
noise. This is achieved through the use of resonators attached to the air intake ducts. the resonators are tuned to
the specific powertrain. The mass air flow (MAF) sensor is attached to the outlet of the air cleaner housing. The
air cleaner life indicator is located on an intake duct between the air cleaner housing and the throttle plate.

SPECIAL TOOLS AND EQUIPMENT

SPECIAL TOOLS

Special Tools

Illustration

Tool Number/Description

GE 41415-50

Fuel Tank Cap Adapter

J 23738-A

Vacuum Pump

J 26792

Spark Tester

2004 Hummer H2

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

J 34142-B

Test Lamp

J 34730-E

Fuel Pressure Gauge Kit

J 34730-1A

Fuel Pressure Gauge

J 34730-405

Injector Test Lamp

2004 Hummer H2

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

J 35616-A

Connector Test Adapter Kit

J 37088-A

Fuel Line Quick Connect Separator

J 37287

Inlet and Return Fuel Line Shut-off Adapters

J 38500-A

Fuel Injector Cleaner

2004 Hummer H2

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