Chevrolet Silverado / GMC Sierra. Service manual — part 2231

Circuit/System Description

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/navigation antenna and cellular antenna coax.

Reference Information

Schematic Reference

OnStar Schematics

Connector End View Reference

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 for scan tool information

Circuit/System Testing

1. Ignition OFF, disconnect the X2 harness connector at the CIM.

Low Reference
1. No (or Noisy) OnStar® Audio

2008 Chevrolet Silverado 1500

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

Silverado, Sierra & Silverado

2. Ignition ON, test for less than 5 mV AC between the signal circuit terminal 1 and ground.

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

3. Install a DMM between the signal circuit terminal 1 and ground. Set the DMM to capture

AC voltage using the MIN MAX function.

4. Press the voice recognition button. Verify the DMM captured greater than 20 mV AC.

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.

5. Install a DMM between the signal circuit terminal 1 and the low reference circuit terminal

2. Set the DMM to capture AC voltage using the MIN MAX function.

6. Press the voice recognition button. Verify the DMM captured greater than 20 mV AC.

If less than the specified range, test the low reference circuit for an open/high
resistance. If the circuit tests normal, replace the radio.

7. If all circuits test normal, replace the CIM.

Repair Procedures

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Control Module References for Radio or CIM replacement, setup, and programming

NO GLOBAL POSITIONING SYSTEM (GPS) RECEPTION

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.

Reference Information

Schematic Reference

Radio/Navigation System Schematics

Connector End View Reference

Component Connector End Views

2008 Chevrolet Silverado 1500

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

Silverado, Sierra & Silverado

Electrical Information Reference

Circuit Testing

Connector Repairs

Testing for Intermittent Conditions and Poor Connections

Wiring Repairs

Scan Tool Reference

Control Module References

Circuit/System Testing

1. Remove the GPS antenna and cable and place it outside the vehicle. Verify the GPS

reception is operational within 5 minutes.

If GPS becomes operational, remove any suspect window tint or objects that may
obstruct the GPS signal.

2. Replace the GPS antenna. Verify the GPS reception is operational within 5 minutes.

If GPS is not operational, replace the radio.

Repair Procedures

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Control Module References for radio replacement, setup, and programming

Global Positioning System (GPS) Antenna Replacement

ONSTAR BUTTON LED INOPERATIVE

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.

Diagnostic Fault Information

IMPORTANT: The global positioning system (GPS) requires a clear line of sight

to the sky to operate properly. In most cases the GPS will not
have reception near tall buildings or inside structures.

2008 Chevrolet Silverado 1500

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

Silverado, Sierra & Silverado

Circuit Description

The OnStar® status LEDs are located with the OnStar buttons. The green LED is illuminated
when the system is ON and operating normally. When the green LED is green and flashing, it is
an indication that a call is in progress. When the red LED is illuminated, a system malfunction is
present. In the event there is a system malfunction and the OnStar® system is still able to make a
call, the LED will flash red during the call. The OnStar® LEDs are controlled by the
communication interface module (CIM) via the keypad green LED signal circuit and the keypad
red LED signal circuit.

Reference Information

Schematic Reference

OnStar Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

OnStar Description and Operation

Electrical Information Reference

Circuit Testing

Connector Repairs

Circuit

Short to

Ground

Open/High

Resistance

Short to

Voltage

Signal

Performance

Keypad Supply Voltage

B2476 00

B2476 00

B2476 00

-

Keypad Green LED Signal

1

1

2

-

Keypad Red LED Signal

1

1

2

-

Keypad Signal

3

3

-

-

Inside Rearview Mirror
Ground

-

1

-

-

1. OnStar® LED Inoperative
2. LED Illuminated At All Times
3. OnStar® Buttons Inoperative

2008 Chevrolet Silverado 1500

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

Silverado, Sierra & Silverado