B2455

DTC B2455

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle (Initial Inspection and Diagnostic Overview) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Initial Inspection and Diagnostic Overview) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Initial Inspection and Diagnostic Overview) provide an overview of each diagnostic category.



DTC Descriptor
DTC B2455 00
- Cellular Phone Microphone Circuit




Diagnostic Fault Information






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 fused, battery voltage circuit connected through the vehicle wiring to the 3-button OnStar(R) assembly located on the inside rearview mirror. The VCIM and radio are attached by means of coax cables to the cellular and navigation antennas. 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(R) 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 serial data bus. 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(R) keypress is made, a class 2 serial data message is sent to the audio system to mute all radio functions and transmit OnStar(R) originated audio. After the audio system is muted, the OnStar(R) 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(R) 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.


Conditions for Running the DTC

* Radio ON.
* Battery voltage must be between 9-16 volts.



Conditions for Setting the DTC

* The VCIM detects a short to voltage in the cellular microphone signal circuit for 10 seconds or greater.
* The VCIM detects an open/high resistance in the drain wire circuit for 10 seconds or greater.



Actions Taken When the DTC Sets

* The OnStar(R) status LED turns red.
* The VCIM will not receive a signal from the microphone.
* Calls can be placed but the caller cannot be heard.



Conditions for Clearing the DTC

* The condition responsible for setting the DTC no longer exists.
* A history DTC will clear once 50 consecutive malfunction-free ignition cycles have occurred.


Schematic Reference

OnStar Schematics (OnStar Schematics)
Connector End View Reference

Component Connector End Views (Connector Views)
Description and Operation

OnStar Description and Operation (OnStar Description and Operation)
Electrical Information Reference

* Circuit Testing (Component Tests and General Diagnostics)
* Connector Repairs (Component Tests and General Diagnostics)
* Testing for Intermittent Conditions and Poor Connections (Component Tests and General Diagnostics)
* Wiring Repairs (Component Tests and General Diagnostics)

Scan Tool Reference

Control Module References (Programming and Relearning) for scan tool information


Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the cellular microphone.
2. Ignition ON, test for 8.5-9.5 volts between the cellular microphone signal circuit terminal 3 and ground.

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


• 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 VCIM.

3. Ignition ON, test for 8.5-9.5 volts between the cellular microphone signal circuit terminal 3 and the drain wire circuit terminal 2.

• If less than the specified range, test the drain wire circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the VCIM.

4. If all circuits test normal, replace the cellular microphone.



Repair Instructions

Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.

* Mobile Telephone Microphone Replacement (Service and Repair)
* Control Module References (Programming and Relearning) for VCIM replacement, setup, and programming