Hummer H2. Manual — part 1479

Fig. 190: MAF/IAT Sensor & Air Cleaner Assembly
Courtesy of GENERAL MOTORS CORP.

1. Loosen the clamp and separate the air cleaner resonator outlet duct from the mass air flow/intake air

temperature (MAF/IAT) sensor assembly.

2. Loosen the clamp and separate the air cleaner resonator outlet duct from the throttle body assembly.

3. Remove the air cleaner resonator outlet duct.

2004 Hummer H2

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

Installation Procedure

Fig. 191: MAF/IAT Sensor & Air Cleaner Assembly
Courtesy of GENERAL MOTORS CORP.

1. Install the air cleaner resonator outlet duct to the throttle body assembly and the MAF/IAT sensor

assembly.

2. Tighten the clamps at the throttle body assembly and the MAF/IAT sensor assembly.

2004 Hummer H2

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

DESCRIPTION AND OPERATION

POWERTRAIN CONTROL MODULE (PCM) DESCRIPTION

Powertrain

The powertrain has electronic controls to reduce exhaust emissions while maintaining excellent driveability and
fuel economy. The powertrain control module (PCM) is the control center of this system. The PCM monitors
numerous engine and vehicle functions. The PCM constantly looks at the information from various sensors and
other inputs, and controls the systems that affect vehicle performance and emissions. The PCM also performs
the diagnostic tests on various parts of the system. The PCM can recognize operational problems and alert the
driver via the malfunction indicator lamp (MIL). When the PCM detects a malfunction, the PCM stores a
diagnostic trouble code (DTC). The problem area is identified by the particular DTC that is set. The control
module supplies a buffered voltage to various sensors and switches. Review the components and wiring
diagrams in order to determine which systems are controlled by the PCM.

The following are some of the functions that the PCM controls:

z

The engine fueling

z

The ignition control (IC)

z

The knock sensor (KS) system

z

The evaporative emissions (EVAP) system

z

The secondary air injection (AIR) system (if equipped)

z

The exhaust gas recirculation (EGR) system

z

The automatic transmission functions

z

The generator

z

The A/C clutch control

z

The cooling fan control

Powertrain Control Module Function

The powertrain control module (PCM) constantly looks at the information from various sensors and other inputs
and controls systems that affect vehicle performance and emissions. The PCM also performs diagnostic tests on
various parts of the system. The PCM can recognize operational problems and alert the driver via the
malfunction indicator lamp (MIL). When the PCM detects a malfunction, the PCM stores a diagnostic trouble
code (DTC). The problem area is identified by the particular DTC that is set. The control module supplies a
buffered voltage to various sensors and switches. The input and output devices in the PCM include analog-to-
digital converters, signal buffers, counters, and output drivers. The output drivers are electronic switches that
complete a ground or voltage circuit when turned on. Most PCM controlled components are operated via output
drivers. The PCM monitors these driver circuits for proper operation and, in most cases, can set a DTC
corresponding to the controlled device if a problem is detected.

Malfunction Indicator Lamp (MIL) Operation

The malfunction indicator lamp (MIL) is located in the instrument panel cluster. The MIL will display as either

2004 Hummer H2

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

SERVICE ENGINE SOON or one of the following symbols when commanded ON:

Fig. 192: Identifying MIL Symbol
Courtesy of GENERAL MOTORS CORP.

2004 Hummer H2

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