Chevrolet Silverado / GMC Sierra. Manual

should not be used in the STUD 1 Fuse 70 position of the underhood fuse block, if the vehicle is
equipped with an auxiliary battery. A plastic plug may be installed in this position instead of a
fuse. If a fuse is installed in this position, the accessories will discharge the primary battery in
addition to the auxiliary battery.

Instrument Panel Cluster (IPC) Operation

Charge Indicator Operation

The instrument panel cluster (IPC) illuminates the charge indicator and displays a warning
message in the driver information center (DIC) when the one or more of the following occurs:

The engine control module (ECM) detects that the generator output is less than 11 volts or
greater than 16 volts. The IPC receives a GMLAN message from the ECM requesting
illumination.

The BCM determines that the system voltage is less than 11 volts or greater than 16 volts.

The IPC receives a GMLAN 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.

Battery Voltage Gauge Operation

The IPC displays the system voltage as received from the BCM over the GMLAN serial data
circuit. If there is no communication with the BCM then the gauge will indicate minimum.

This vehicle is equipped with a regulated voltage control (RVC) system. This system turns off the
generator when it is not required in order to improve fuel economy. The generator will turn back
on when additional voltage is required. This will cause the voltmeter to fluctuate between 12 and
14 volts as opposed to non-regulated systems which usually maintain a more consistent reading of
14 volts. This fluctuation with the RVC system is normal system operation and NO repairs should
be attempted.

SERVICE BATTERY CHARGING SYSTEM

The BCM and the ECM will send a GMLAN message to the DIC for the SERVICE BATTERY
CHARGING SYSTEM message to be displayed. It is commanded ON when a charging system
DTC is a current DTC. The message is turned OFF when the conditions for clearing the DTC
have been met.

2008 Chevrolet Silverado 1500

2008 ENGINE Engine Electrical - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado

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.

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.

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 10.9 V

First level idle

boost requested

Idle Boost 1 End

Greater Than -10°

C (+5°F)

Greater Than 12

Battery has a net
loss less than 0.2

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 10.9 V

Second level idle

boost requested

Idle Boost 2 End

Greater Than 12

Battery has a net
loss less than 0.8

Second level idle

boost request

cancelled

Idle Boost 3

Start

Battery has a net

loss of 10.0 AH

Third level idle
boost requested

Idle Boost 3

Less Than 10.9 V

Third level idle

2008 Chevrolet Silverado 1500

2008 ENGINE Engine Electrical - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado

STARTING SYSTEM DESCRIPTION AND OPERATION

The starter motors are non-repairable starter motors. They have pole pieces that are arranged
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 START relay opens and
battery voltage is removed from the starter solenoid S terminal. 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 12-volt 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 crank relay. When this occurs, battery positive
voltage is supplied through the switch side of the crank relay to the S terminal of the starter
solenoid.

Start

boost requested

Idle Boost 3 End

Greater Than 12

Battery has a net

loss of less than 6

Third level idle

boost request

cancelled

2008 Chevrolet Silverado 1500

2008 ENGINE Engine Electrical - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado

SPECIAL TOOLS AND EQUIPMENT

SPECIAL TOOLS

Illustration

Tool Number/Description

J 38758

Parasitic Draw Test Switch

J 41450-B

Universal CS Generator Tester Harness

J 42000

Battery Tester

2008 Chevrolet Silverado 1500

2008 ENGINE Engine Electrical - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado

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Chevrolet Silverado / GMC Sierra. Manual - part 1789