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 communication interface module (CIM) is a cellular device that allows the user to communicate data and voice signals over the national cellular network. When an OnStar keypress is made, the CIM activates and connects the 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.

• | 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.

### 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 Verification

1. Verify that the cellular antenna and cellular antenna coupling assembly are not damaged.

⇒ | If damage is found, repair or replace as necessary.

2. Ignition ON, press the OnStar® Call Center button. Verify the system activates and the message Connecting to OnStar® is heard.

⇒ | If the system does not activate and the message is not heard, refer to OnStar One or More Buttons Inoperative .

3. If the system activates but does not connect with the OnStar® call center, refer to Circuit/System testing.

### Circuit/System Testing

1. Ignition OFF, disconnect the cellular antenna coax from the CIM module and the cellular antenna.
2. Ignition ON, test for less than 1 volt between the antenna coax center terminal and ground.

⇒ | If greater than the specified range, replace the antenna coax.

3. Ignition ON, test for less than 1 volt between the antenna coax outer shield and ground.

⇒ | If greater than the specified range, replace the antenna coax.

4. Test for infinite resistance between the antenna coax center terminal and ground.

⇒ | If less than the specified value, replace the antenna coax

5. Test for infinite resistance between the antenna coax outer shield and ground.

⇒ | If less than the specified value, replace the antenna coax

6. Test for less than 5 ohms at the cellular antenna coax center terminal from end to end.

⇒ | If greater than specified value, replace the cellular antenna coax cable.

7. Test for less than 5 ohms at the cellular antenna coax outer shield from end to end.

⇒ | If greater than specified value, replace the cellular antenna coax cable.

8. Test for infinite resistance between the antenna coax center terminal and the outer shield.

⇒ | If less than specified value, replace the cellular antenna coax cable.

9. If coax cable tests normal, replace the cellular antenna.
10. Press the OnStar® Call Center button. Verify the system connects to the OnStar® call center.

⇒ | If a connection is not made to the OnStar® call center, replace the CIM.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Radio Antenna Base Replacement

• | Control Module References for CIM replacement, setup, and programming