Hummer H3. Manual — part 70

The IPC determines that the system voltage is less than 11 volts or greater than 16 volts. The
IPC receives a class 2 message from the body control module (BCM) indicating there is a
system voltage range concern.

The IPC performs the displays test at the start of each ignition cycle. The indicator
illuminates for approximately 3 seconds.

The ignition is ON, with the engine OFF.

The generator battery control module determines there is a fault and sends a class 2 message
to the IPC to illuminate the charge indicator.

Charging System Failure

The generator battery control module will send a message to the IPC for the CHARGING
SYSTEM FAILURE message to be displayed. It is commanded ON when DTC B1487 sets. The
message is turned off when the conditions for clearing the DTC have been met and after an
ignition cycle.

Service Charging System

The generator battery control module will send a class 2 message to the IPC for the SERVICE
CHARGING SYSTEM message to be displayed. It is commanded ON when DTC B1390,
B1488, B1492, or B1516 sets. The message is turned OFF when the conditions for clearing the
DTC have been met and after an ignition cycle.

Voltmeter Operation

The IPC displays the system voltage as detected at the ignition 1 input of the IPC. When the
engine is ON, the gage should be between 10-16 volts. The voltmeter will be noticeably different
than previous model year vehicle as far as voltage fluctuations. If there is a concern with gage
operation ensure to compare to a known good like vehicle.

ELECTRICAL POWER MANAGEMENT DESCRIPTION AND OPERATION

Electrical Power Management

The electrical power management (EPM) is used to monitor and control the charging system and
alert the driver of possible problems within the charging system. The EPM system makes the most
efficient use of the generator output, improves the battery state of charge (SOC), extends battery
life.

see if they set a DTC when the battery voltage is too high or too
low.

2008 Hummer H3

2008 ENGINE Engine Electrical - H3

The idle boost operation is a means of improving generator performance during a low voltage or
low battery SOC condition.

Idle boost is activated in incremental steps, idle boost 1 must be active before idle boost 2 can be
active. The criteria used by the body control module (BCM) to regulate EPM are outlined below:

STARTING SYSTEM DESCRIPTION AND OPERATION

The starter motors are non-repairable starter motors. They have pole pieces that are arranged

Function

Battery

Temperature

Calculation

Battery Voltage

Calculation

Amp-hour

Calculation

Action Taken

Idle Boost 1 Start

Less Than -15°C

(5°F)

Less Than 13 V

-

First level Idle

boost requested

Idle Boost 1 Start

-

-

Battery has a net

loss greater than

0.6 AH

First level Idle

boost requested

Idle Boost 1 Start

-

Less Than 11 V

-

First level Idle

boost requested

Idle Boost 1 End

Greater Than -15°

C (5°F)

Greater Than 12

V

Battery has a net
loss less than 0.2

AH

First level Idle

boost request

cancelled

Idle Boost 2 Start

-

-

Battery has a net

loss greater than

1.6 AH

Second level

Idle boost

requested

Idle Boost 2 Start

-

Less Than 11 V

-

Second level

Idle boost

requested

Idle Boost 2 End

-

Greater Than 12

V

Battery has a net
loss less than 0.8

AH

Second level

Idle boost

request cancelled

Idle Boost 3 Start

-

-

Battery has a net

loss of 10 AH

Third level Idle
boost requested

Idle Boost 3 Start

-

Less Than 11 V

-

Third level Idle
boost requested

Idle Boost 3 End

-

Greater Than 12

V

Battery has a net

loss of less than 6

AH

Third level Idle

boost request

cancelled

2008 Hummer H3

2008 ENGINE Engine Electrical - H3

around the armature. Both solenoid windings are energized. The pull-in winding circuit is
completed to the ground through the starter motor. The windings work together magnetically to
pull and hold in the plunger. The plunger moves the shift lever. This action causes the starter drive
assembly to rotate on the armature shaft spline as it engages with the flywheel ring gear on the
engine. Moving at the same time, the plunger also closes the solenoid switch contacts in the starter
solenoid. Full battery voltage is applied directly to the starter motor and it cranks the engine.

As soon as the solenoid switch contacts close, current stops flowing thorough the pull-in winding
because battery voltage is applied to both ends of the windings. The hold-in winding remains
energized. Its magnetic field is strong enough to hold the plunger, shift lever, starter drive
assembly, and solenoid switch contacts in place to continue cranking the engine. When the engine
starts, pinion overrun protects the armature from excessive speed until the switch is opened.

When the ignition switch is released from the START position, the PCM CNTRL relay opens and
battery voltage is removed from the starter solenoid terminal A X1. Current flows from the motor
contacts through both windings to the ground at the end of the hold-in winding. However, the
direction of the current flow through the pull-in winding is now opposite the direction of the
current flow when the winding was first energized.

The magnetic fields of the pull-in and hold-in windings now oppose one another. This action of
the windings, along with the help of the return spring, causes the starter drive assembly to
disengage and the solenoid switch contacts to open simultaneously. As soon as the contacts open,
the starter circuit is turned off.

Circuit Description (Key Start)

When the ignition switch is placed in the Start position, a discrete signal is supplied to the body
control module (BCM) notifying it that the ignition is in the start position. The BCM then sends a
message to the engine control module (ECM) notifying it that crank has been requested. The
ECM verifies that the transmission is in Park or Neutral. If it is, the ECM then supplies 12 volts
to the control circuit of the PCM CNTRL relay. When this occurs, battery positive voltage is
supplied through the switch side of the PCM CNTRL relay to terminal A X1 of the starter
solenoid.

SPECIAL TOOLS AND EQUIPMENT

SPECIAL TOOLS

Illustration

Tool Number/Description

2008 Hummer H3

2008 ENGINE Engine Electrical - H3

J 38758

Parasitic Draw Test Switch

J 42000

Battery Tester

2008 Hummer H3

2008 ENGINE Engine Electrical - H3