Unable to Contact OnStar Call Center

Cellular, Entertainment, and Navigation | Diagnostic Information and Procedures | Document ID: 5197618 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. DTC Descriptors DTC B178C Cell Phone Antenna Coaxial Signal For symptom byte information refer to: Symptom Byte List Diagnostic Fault Information

Circuit	Short to Ground	Open/High Resistance	Short to Voltage	Signal Performanc
Coax Cable	B178C 11	B178C 13	B178C 12	—

Circuit/System Description The primary cellular phone antenna element, which is part of the T4P High Frequency Antenna, is connected to the K73 Telematic Control Module (violet connector) via a shielded coaxial cable. Cellular communication takes place on both the primary cellular antenna signal circuit and the GPS/secondary cellular antenna signal circuit. This diagnostic only applies to the primary cellular antenna signal circuit. Internal to the antenna on the cellular antenna signal circuit resistance is used to apply a load, which the communication interface module uses to detect the presence of the antenna. Conditions for Running the DTC Ignition ON. System voltage is between 9-16 V. Conditions for Setting the DTC B178C 11 Short to ground on the primary cellular antenna signal circuit. B178C 12 Short to voltage on the primary cellular antenna signal circuit. B178C 13 Open on the primary cellular antenna signal circuit. Action Taken When the DTC Sets The OnStar® status LED turns red. Conditions for Clearing the DTC The K73 Telematic Control Module detects the presence of a cellular antenna The K73 Telematic Control Module detects the presence of a cellular antenna. A history DTC clears after 100 malfunction-free ignition cycles. Reference Information Schematic Reference OnStar/Telematics Schematics Connector End View Reference Master Electrical Component List 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 Special Tools EL-49903-1 Test Antenna Navn-Cell Comn EL-52552 COAX FAKRA Cable Adaptor Kit Circuit/System Testing

Note

The vehicle may be equipped with sectioned coax. Test each section and replace only the faulty section, not the entire length of coax. The following verification requires the vehicle to be outside with an unobstructed view of the southern sky. Allow 5 min after turning the ignition ON for the GPS satellites to acquire vehicle signal.

1. Ignition OFF, disconnect the violet primary cellular coax cable connector at the K73 Telematic Control Module. It may take up to 2 min for all vehicle systems to power down.
2. Using the EL-49903-1 Test Antenna Navn-Cell Comn connect the violet coax cable to the K73 Telematic Control Module. Place the test antenna on the roof of the vehicle, ignition ON/vehicle in Service Mode.
3. Verify the DTC does not set or a call can be completed to the OnStar Call Center while operating the vehicle within the conditions for running the DTC. ⇒ If the DTC sets or a call can not be completed to the OnStar Call Center Replace the K73 Telematic Control Module. ⇓ If the DTC does not set or a call can be completed to the OnStar Call Center
4. Ignition OFF.
5. Disconnect the EL-49903-1 Test Antenna Navn-Cell Comn from the K73 Telematic Control Module.
6. Disconnect the primary cellular coax cable from the T4P High Frequency Antenna.
7. Test the coax cable. Refer to Component Testing. ⇒ If the coax cable does not pass the test Replace the coax cable. ⇓ If the coax cable passes the test
8. Test or replace the T4P High Frequency Antenna. Component Testing

Note

Before testing the coax cable, check the cable exterior for being pinched, cut, damaged, or having loose connections at the components, which can cause reception issues. Coax Cable Test

1. Ignition OFF, disconnect the coax cable at both components.
2. Locate the appropriate pinout adaptor and load test loop adaptor from EL-52552 COAX FAKRA Cable Adaptor Kit.
3. Connect the 2 adaptors together, measure and record the resistance between the terminals at the pinout adaptor.
4. Disconnect the 2 adaptors and connect each one to the appropriate end of the coax cable.
5. At the pinout adapter, measure the total resistance of the coax cable loop including the connected load test adaptor. ⇒ If not within 5 Ω of the reading from step 3. Replace the coax cable ⇓ If within 5 Ω of the reading from step 3.
6. All OK. Repair Instructions Perform the Diagnostic Repair Verification after completing the repair procedure. High Frequency Antenna Replacement Refer to: Control Module References for control module replacement, setup, and programming