For 1990-2009 cars

### 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) has the capability of commanding the horn, initiating door lock/unlock and operating the exterior lamps using the serial data circuits.

### Reference Information

#### Schematic Reference

OnStar Schematics

#### Connector End View Reference

Entertainment/Communication 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

Scan Tool Data List

### 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 that has since been corrected.

### Circuit/System Verification

Important: It is necessary to inform the OnStar® Call Center advisor that this call is for vehicle diagnostic purposes.

1. Observe that the horn, lights, and the doors locks on the vehicle operate properly.

⇒ | If the applicable system does not operate properly, refer to Diagnostic Starting Point - Horns , Diagnostic Starting Point - Lighting , or Symptoms - Remote Functions respectively.

2. Contact the OnStar® Call Center by pressing the blue OnStar® button. Verify with the OnStar® advisor that all of the remote functions (door locks, lights, or horn) work.

⇒ | If the remote functions do not work, use the scan tool to access the STID and ESN and contact the General Motors Technical Assistance Center.