Chevrolet Silverado / GMC Sierra. Service manual — part 2237

Without Amplifier (UQ3)

1. Ignition OFF, disconnect the harness connector at the appropriate speaker.

2. Radio ON, test for 5.0-7.5 volts between the speaker circuit terminal A and ground.

If greater than the specified range, test the speaker circuit for a short to voltage. If the
circuit tests normal, replace the radio.

If less than the specified range, test the signal circuit for a short to ground or an
open/high resistance. If the circuit tests normal, replace the radio.

3. Test for 5.0-7.5 volts between the speaker circuit terminal B and ground.

If greater than the specified range, test the speaker circuit for a short to voltage. If the
circuit tests normal, replace the radio.

If less than the specified range, test the speaker circuit for a short to ground or an
open/high resistance. If the circuit tests normal, replace the radio.

4. If the vehicle is equipped with UK6 Rear Seat Audio and the concern is with a rear speaker,

Test the speaker circuits between the radio and the RSA control.

5. If all circuits test normal, test or replace the speaker.

With Amplifier (UQA/UQS)

1. Ignition OFF, disconnect the X1and X3 harness connectors at the amplifier.

2. Radio ON, Rear Seat Audio OFF, test for 5.0-7.5 volts between the appropriate speaker

circuit terminal listed below and ground.

With UQA

Left front speaker control- Connector X2, terminal 4

Left front speaker control- Connector X2, terminal 3

Right front speaker control - Connector X2, terminal 2

Right front speaker control - Connector X2, terminal 1

Front center speaker control - Connector X2, terminal 13 (w/ Y91)

Front center speaker control - Connector X2, terminal 1 2(w/ Y91)

Left subwoofer speaker control- Connector X1, terminal 7

Left subwoofer speaker control- Connector X1, terminal 3

Right subwoofer speaker control- Connector X1, terminal 2

Right subwoofer speaker control- Connector X1, terminal 6

2008 Chevrolet Silverado 1500

2008 ACCESSORIES & EQUIPMENT Cellular, Entertainment, and Navigation - Cab & Chassis Sierra, Cab & Chassis

Silverado, Sierra & Silverado

With UQS

Left front speaker control- Connector X2, terminal 4

Left front speaker control- Connector X2, terminal 5

Right front speaker control - Connector X2, terminal 7

Right front speaker control - Connector X2, terminal 8

Front center speaker control - Connector X2, terminal 13 (w/ Y91)

Front center speaker control - Connector X2, terminal 1 2(w/ Y91)

Left subwoofer speaker control- Connector X1, terminal 1

Left subwoofer speaker control- Connector X1, terminal 2

Right subwoofer speaker control- Connector X1, terminal 3

Right subwoofer speaker control- Connector X1, terminal 7

If greater than the specified range, test the signal circuit for a short to voltage. If the
circuit tests normal, replace the radio.

If less than the specified range, test the signal circuit for a short to ground or an
open/high resistance. If the circuit tests normal, replace the radio.

If all circuits test normal, replace the amplifier.

Repair Procedures

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Speaker Replacement Reference

Control Module References for Amplifier and Radio replacement, setup, and
programming

UNABLE TO CONTACT ONSTAR CALL CENTER

Diagnostic Instructions

Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

Review Strategy Based Diagnosis for an overview of the diagnostic approach.

Diagnostic Procedure Instructions provides an overview of each diagnostic category.

Circuit/System Description

The vehicle communication interface module (VCIM) is a 3-watt cellular device that allows the
user to communicate data and voice signals over the national cellular network. It is powered by a

2008 Chevrolet Silverado 1500

2008 ACCESSORIES & EQUIPMENT Cellular, Entertainment, and Navigation - Cab & Chassis Sierra, Cab & Chassis

Silverado, Sierra & Silverado

fused, battery positive, voltage circuit connected through the vehicle wiring to the 3-button
assembly and the radio, and attached by means of coax cables to the cellular and navigation
antennas. Ground for the module is accomplished by means of dedicated circuits that are routed
with body wiring systems to chassis ground points. The module houses 2 modems, one to process
global positioning system (GPS) data, and the other for cellular information. Satellites orbiting
earth are constantly transmitting signals of their current location, from which the OnStar® system
is able to pinpoint its own location. The navigation antenna receives these GPS signals and
provides the data to the VCIM to be processed. The VCIM communicates with the rest of the
vehicle over the class 2 or GMLAN serial data bus, depending upon the serial data architecture of
the vehicle. The ignition state is determined by the VCIM through class 2 or GMLAN messaging.
The module also has the capability of commanding the horn, initiating door lock/unlock, and
operating the exterior lamps using the serial data circuits. When an OnStar® keypress is made, a
serial data message is sent to the audio system to mute all radio functions and transmit OnStar®
originated audio. After the audio system is muted, the OnStar® signals are transmitted to the
audio system on the cellular telephone voice signal circuit, and returned to the module on the
cellular telephone voice low reference circuit. The cellular modem connects the OnStar® system
to the cellular carriers communication system by interacting with the national cellular
infrastructure. The module sends and receives all cellular communications over the cellular
antenna and cellular antenna coax.

Diagnostic Aids

The customer concern may have been due to a lack of cellular service in a given area. A
failure in the National Cellular Network infrastructure at the time of the customers failed
connection that has since been repaired may also have been the cause.

If an OnStar® emergency call is able to successfully connect the vehicle to the OnStar®
Call Center when an OnStar® Call Center button press is not, there may be a failure in the
ability of the OnStar® system in the vehicle to be recognized by the local cellular carrier.

If the prompt "OnStar® request ended" is heard, without pressing the white dot button at
the end of the OnStar® keypress, the OnStar® system at one time has made a successful
cellular connection, but was unable to complete the call. If repeated calls are placed with
this result, contact General Motors Technical Assistance Center.

Reference Information

Schematic Reference

OnStar Schematics

Connector End View Reference

2008 Chevrolet Silverado 1500

2008 ACCESSORIES & EQUIPMENT Cellular, Entertainment, and Navigation - Cab & Chassis Sierra, Cab & Chassis

Silverado, Sierra & Silverado

Component Connector End Views

Description and Operation

OnStar Description and Operation

Electrical Information Reference

Circuit Testing

Connector Repairs

Testing for Intermittent Conditions and Poor Connections

Wiring Repairs

Scan Tool Reference

Control Module References

Circuit/System Verification

1. Press the OnStar® Call Center button. Verify a connection is not made with the OnStar®

Call Center.

If a connection is made with the OnStar® Call Center, go to Diagnostic Aids.

2. Listen for other tones or cellular messages rather than the normal progression tones or the

Unable to Contact OnStar® prompt.

If no other tones or cellular messages are heard other than the normal progression tones
or the Unable to Contact OnStar® prompt, go to Component Testing.

3. Record all messages heard from the OnStar® Call Center button press.

4. Press the OnStar® emergency button. Verify a connection to the OnStar® Call Center is

made within 10 minutes.

IMPORTANT:

It is important to have the vehicle in an open outside area
where a cellular call can be successfully placed and GPS
data can be received from satellites.

Placing an emergency call to the OnStar® Call Center should
only be made if the diagnosis of the system leads to step 4.
Immediately after an OnStar® advisor picks up the call, they
should be told that this call is for diagnostic purposes only
and there is no emergency.

2008 Chevrolet Silverado 1500

2008 ACCESSORIES & EQUIPMENT Cellular, Entertainment, and Navigation - Cab & Chassis Sierra, Cab & Chassis

Silverado, Sierra & Silverado