Hummer H2. Manual - part 1480

Fig. 193: MIL ON (Check)
Courtesy of GENERAL MOTORS CORP.

The MIL indicates that an emissions related fault has occurred and vehicle service is required.

The following is a list of the modes of operation for the MIL:

The MIL illuminates when the ignition is turned ON, with the engine OFF. This is a bulb test to ensure
the MIL is able to illuminate.

The MIL turns OFF after the engine is started if a diagnostic fault is not present.

The MIL remains illuminated after the engine is started if the control module detects a fault. A diagnostic
trouble code (DTC) is stored any time the control module illuminates the MIL due to an emissions related
fault. The MIL turns OFF after three consecutive ignition cycles in which a Test Passed has been reported

2004 Hummer H2

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

for the diagnostic test that originally caused the MIL to illuminate.

The MIL flashes if the control module detects a misfire condition which could damage the catalytic
converter.

When the MIL is illuminated and the engine stalls, the MIL will remain illuminated as long as the
ignition is ON.

When the MIL is not illuminated and the engine stalls, the MIL will not illuminate until the ignition is
cycled OFF and then ON.

Trip

A trip is an interval of time during which the diagnostic test runs. A trip may consist of only a key cycle to
power up the powertrain control module (PCM), allow the diagnostic to run, then cycle the key off to power
down the PCM. A trip may also involve a PCM power up, meeting specific conditions to run the diagnostic test,
then powering down the PCM. The definition of a trip depends upon the diagnostic. Some diagnostic tests run
only once per trip (i.e., catalyst monitor) while other tests run continuously during each trip (i.e., misfire).

Warm-Up Cycle

The powertrain control module (PCM) uses warm-up cycles to run some diagnostics and to clear any diagnostic
trouble codes (DTCs). A warm-up cycle occurs when the engine coolant temperature increases 22° C (40° F)
from the start-up temperature. The engine coolant must also achieve a minimum temperature of 71° C (160° F).
The PCM counts the number of warm-up cycles in order to clear the malfunction indicator lamp (MIL). The
PCM will clear the DTCs when 40 consecutive warm-up cycles occur without a malfunction.

Diagnostic Trouble Codes (DTCs)

The powertrain control module (PCM) is programmed with test routines that test the operation of the various
systems the PCM controls. Some tests monitor internal PCM functions. Many tests are run continuously. Other
tests run only under specific conditions, referred to as Conditions for Running the DTC. When the vehicle is
operating within the conditions for running a particular test, the PCM monitors certain parameters and
determines if the values are within an expected range. The parameters and values considered outside the range
of normal operation are listed as Conditions for Setting the DTC. When the Conditions for Setting the DTC
occur, the PCM executes the Action Taken When the DTC Sets. Some DTCs alert the driver via the
malfunction indicator lamp (MIL) or a message. Other DTCs do not trigger a driver warning, but are stored in
memory. The PCM also saves data and input parameters when most DTCs are set. This data is stored in the
Freeze Frame and/or Failure Records.

The DTCs are categorized by type. The DTC type is determined by the MIL operation and the manner in which
the fault data is stored when a particular DTC fails. In some cases there may be exceptions to this structure.
Therefore, when diagnosing the system it is important to read the Action Taken When the DTC Sets and the
Conditions for Clearing the DTC in the supporting text.

There are different types of DTCs and different actions taken when the DTCs set. Refer to Diagnostic Trouble
Code (DTC) Type Definitions for a description of the general characteristics of each DTC type.

DTC Status

2004 Hummer H2

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

When the scan tool displays a DTC, the status of the DTC is also displayed. The following DTC statuses are
indicated only when they apply to the DTC that is set.

Fail This Ign. (Fail This Ignition)

Indicates that this DTC failed during the present ignition cycle.

Last Test Fail

Indicates that this DTC failed the last time the test ran.

MIL Request

Indicates that this DTC is currently requesting the malfunction indicator lamp (MIL). This selection will
report type B DTCs only when they have requested the MIL (failed twice).

Test Fail SCC (Test Failed Since Code Clear)

Indicates that this DTC that has reported a failure since the last time DTCs were cleared.

History

Indicates that the DTC is stored in the powertrain control module (PCM) History memory. Type B DTCs
will not appear in History until they have requested the MIL (failed twice). History will be displayed for
all type A DTCs and type B DTCs (which have requested the MIL) that have failed within the last 40
warm-up cycles. Type C DTCs that have failed within the last 40 warm-up cycles will also appear in
History.

Not Run SCC (Not Run Since Code Clear)

DTCs will be listed in this category if the diagnostic has not run since DTCs were last cleared. This status
is not included with the DTC display since the DTC can not be set if the diagnostic has not run. This
information is displayed when DTC Info is requested using the scan tool.

THROTTLE ACTUATOR CONTROL (TAC) SYSTEM DESCRIPTION

The throttle actuator control (TAC) system delivers improved throttle response and greater reliability and
eliminates the need for mechanical cable. The TAC system performs the following functions:

Accelerator pedal position (APP) sensing

Throttle positioning to meet driver and engine demands

Throttle position sensing

Internal diagnostics

Cruise control functions

Manage TAC electrical power consumption

2004 Hummer H2

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

The TAC system components include the following:

The APP sensors

The throttle body assembly

The TAC module

The powertrain control module (PCM)

Accelerator Pedal Position (APP) Sensor

The accelerator pedal assembly contains 2 individual APP sensors within the assembly. The APP sensors 1 and
2 are potentiometer type sensors, each with the following circuits:

A 5-volt reference circuit

A low reference circuit

A signal circuit

The APP sensors are used to determine the pedal angle. The control module provides each APP sensor a 5-volt
reference circuit and a low reference circuit. The APP sensors then provide the control module with signal
voltage proportional to pedal movement. Both APP sensor signal voltages are low at rest position and increase
as the pedal is applied.

Throttle Body Assembly

The throttle body assembly consists of the throttle body, the throttle position (TP) sensors, and the throttle
actuator motor. The throttle body functions similar to a similar to a conventional throttle body with the
following exceptions:

An electric motor opens and closes the throttle valve.

The throttle blade is spring loaded in both directions and the default position is slightly open.

There are 2 individual TP sensors within the throttle body assembly.

The TP sensors 1 and 2 are potentiometer type sensors, each with the following circuits:

A 5-volt reference circuit

A low reference circuit

A signal circuit

The TP sensors are used to determine the throttle plate angle. The control module provides each TP sensor a 5-
volt reference circuit and a low reference circuit. The TP sensors then provide the control module with signal
voltage proportional to throttle plate movement. Both TP sensor signal voltages are low at closed throttle and
increase as the throttle opens.

Throttle Actuator Control Module

The throttle actuator control (TAC) module is the control center for the throttle actuator control system. The

2004 Hummer H2

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

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