Chevrolet Silverado / GMC Sierra. Service manual — part 2437

warning requests via the GMLAN serial data circuit. If the radio receives multiple audible
warning requests, the warning with the highest priority sounds first. On vehicles without a radio, a
chime module generates the audible warnings and receives audible warning requests via
GMLAN. Either the radio or the chime module is the chime procedure. The following lists the
audible warning priority and the pulse rate:

1. Fast rate chime-200 pulses per minute

2. Medium rate chime-150 pulses per minute

3. Slow rate chime-50 pulses per minute

4. Single chime

Fasten Safety Belt Warning

The chime producer activates the fasten safety belt audible warning as requested by the body
control module (BCM). The BCM sends a GMLAN message to the audio amplifier indicating the
chime frequency at a slow rate and a duration of 8 seconds. The fasten safety belt warning sounds
and the fasten safety belt indicator illuminates when the following occurs:

The ignition switch transitions to ON.

The inflatable restraint sensing and diagnostic module (SDM) detects that the drivers seat
belt is not buckled and the signal is low. The SDM sends a GMLAN message to the BCM
indicating the seat belt status. The instrument panel cluster (IPC) receives a GMLAN
message from the BCM indicating the driver seat belt status.

If the seat belt is buckled when the ignition is turned ON, the chime does not sound. If the seat
belt is buckled while the chime is sounding, the chime stops. If the seat belt is unbuckled after the
initial transition to ON, the chime does not sound.

Lights On Warning

The chime producer activates the lights on warning as requested by the body control module
(BCM). The BCM sends a GMLAN message to the chime producer indicating the chime
frequency of a fast rate and at a continuous duration. The lights on warning sounds when the
following occurs:

The ignition is OFF.

The BCM determines that the driver door is open and the signal circuit is low.

The BCM determines that the headlamp switch is in the park or head position.

Brake Warning

2008 Chevrolet Silverado 1500

2008 ACCESSORIES & EQUIPMENT Displays and Gages - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra &

Silverado

The chime producer activates the brake audible warning as requested by the instrument panel
cluster (IPC). The IPC sends a GMLAN message to the chime producer indicating the chime
frequency of a fast rate and at a continuous duration. The brake warning sounds and the BRAKE
indicator illuminates when the following occurs:

The ignition is ON.

The vehicle speed is greater than 8 km/h (4.9 mph). The IPC receives a GMLAN message
from the engine control module (ECM) indicating the vehicle speed.

The IPC determines that the park brake is engaged and the signal circuit is low.

The brake fluid is low.

The Traction Control System (TCS) and the Vehicle Stability Enhancement System (VSES)
have failed.

Key-In-Ignition Warning

The chime producer activates the key-in-ignition audible warning as requested by the body
control module (BCM). The BCM sends a GMLAN message to the chime producer indicating the
chime frequency of a medium rate and continuous duration. The key-in-ignition warning sounds
when the following occurs:

The ignition switch is OFF.

The BCM determines that the driver door is open and the signal circuit is low. The IPC also
receives a GMLAN message from the BCM indicating the door ajar status

The BCM determines that the key-in-ignition switch is open and the signal circuit is high.
The IPC receives a GMLAN message from the BCM indicating the key-in-ignition status.

Door Ajar Warning

The chime producer activates the door ajar audible warning as requested by the body control
module (BCM). The BCM sends a GMLAN message to the chime producer indicating the chime
frequency of a medium rate and continuous duration. The door ajar warning sounds and the
appropriate door ajar indicator illuminates in the drivers information center (DIC) when the
following occurs:

The BCM determines that a door (driver door, passenger door, left rear door, right rear
door) is open and the signal circuit is low. The IPC also receives a GMLAN message from
the BCM indicating the door ajar status.

The vehicle is not in PARK. The BCM receives a GMLAN message from the engine control
module (ECM)/BCM indicating the gear position.

2008 Chevrolet Silverado 1500

2008 ACCESSORIES & EQUIPMENT Displays and Gages - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra &

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Additional Warnings

The following warnings have an associated instrument panel cluster (IPC) indicator or driver
information center (DIC) message:

Engine Overheated Stop Engine Message-The chime producer activates the audible warning
as requested by the BCM. The BCM sends a GMLAN message to the chime producer
indicating the chime frequency of a fast rate and at a continuous duration.

Engine Power Is Reduced Message-The chime producer activates the audible warning as
requested by the BCM. The BCM sends a GMLAN message to the chime producer
indicating the chime frequency of a medium rate and at a continuous duration.

Fuel Level Low Message-The chime producer activates the audible warning as requested by
the BCM. The BCM sends a GMLAN message to the chime producer indicating the chime
frequency of a fast rate and at a continuous duration.

Hood Open Message-The chime producer activates the audible warning as requested by the
BCM. The BCM sends a GMLAN message to the chime producer indicating the chime
frequency of a medium rate and at a finite duration.

Oil Pressure Indicator-The chime producer activates the audible warning as requested by the
BCM. The BCM sends a GMLAN message to the chime producer indicating the chime
frequency of a fast rate and at a continuous duration.

Park Assist Fault Clean Rear Bumper Message-The chime producer activates the audible
warning as requested by the BCM. The BCM sends a GMLAN message to the chime
producer indicating the chime frequency of a medium rate and at a finite duration.

Rear Access Open Message-The chime producer activates the audible warning as requested
by the BCM. The BCM sends a GMLAN message to the chime producer indicating the
chime frequency of a medium rate and at a finite duration.

Tire Pressure Low Indicator-The chime producer activates the audible warning as requested
by the BCM. The BCM sends a GMLAN message to the chime producer indicating the
chime frequency of a fast rate and at a continuous duration.

Turn Signal Indicators-The chime producer activates the audible warning as requested by
the IPC. The chime produces two different chimes, one when the turn signal turns off and
another when the turn signal turns on.

Vehicle Overspeed Message-The chime producer activates the audible warning as requested
by the BCM. The BCM sends a GMLAN message to the chime producer indicating the
chime frequency of a medium rate and at a finite duration.

Transmission Hot Idle Engine Message-The chime producer activates the audible warning as
requested by the BCM. The BCM sends a GMLAN message to the chime producer
indicating the chime frequency of a fast rate and at a continuous duration.

2008 Chevrolet Silverado 1500

2008 ACCESSORIES & EQUIPMENT Displays and Gages - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra &

Silverado

Refer to Indicator/Warning Message Description and Operation.

COMPASS CALIBRATION AND MAGNETIC VARIANCE

Compass Calibration

Before calibrating the compass, drive the vehicle to an open area that is magnetically clean or
free of large metallic objects such as high tension power lines or large steel buildings. Verify
there are no magnetized roof antennas, magnets on or hanging from the mirror, or any other
magnetized objects on the inside or outside of the vehicle close to the mirror.

1. Start the engine.

2. Press and hold the switch for the compass, which may be depicted as COMP, COMPASS,

or on/off (w/UE1) depending on the type of mirror on the vehicle, until the letter "C" or
"CAL" is displayed.

3. Drive the vehicle in circles at a speed of less than 8 km/h (5 mph) until the "C" or "CAL" is

replaced by a proper vehicle heading. The calibration procedure is now complete.

Compass Magnetic Variation Adjustment

Magnetic variation adjustments are required when the compass displays a constant error in
heading. Variation is the difference between magnetic north and true north due to geographical
location.

IMPORTANT: Before calibrating the compass, make sure the mirror has the

correct zone number. Refer to Compass Magnetic Variation
Adjustment.

2008 Chevrolet Silverado 1500

2008 ACCESSORIES & EQUIPMENT Displays and Gages - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra &

Silverado