Buick Regal: DTC B125B

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.
• Refer to Diagnostic Procedure Instructions for an overview of each diagnostic category.

DTC Descriptors

DTC B125B 02

Antenna 2 Signal Circuit Short to Ground

DTC B125B 04

Antenna 2 Signal Circuit Open Circuit

Diagnostic Fault Information

1. May exhibit possible FM interference.

Circuit/System Description

Quarter Window Antenna

The active antenna system uses an integral antenna applied as an applique to the rear quarter window.

The antenna module receives FM2 signals from the rear quarter window. The radio antenna module is enabled when the radio is turned on. The radio provides battery voltage to the antenna module using the center conductor of the antenna coaxial cable. When a 12 V signal is seen by the module on the center conductor of the antenna coax, FM2 signals are amplified.

Rear Window Antenna

The active antenna system uses an integral antenna applied as an applique to the rear glass. The antenna module receives FM2 signals from the rear glass antenna. The radio antenna module is enabled when the radio is turned on. The radio provides battery voltage to the antenna module using the center conductor of the antenna coaxial cable. When a 12 V signal is seen by the module on the center conductor of the antenna coax, FM2 signals are amplified.

Conditions for Running the DTC

• Ignition ON.
• Battery voltage must be between 9 - 16 V.

Conditions for Setting the DTC

B125B 02

The radio detects a short to ground in the antenna 2 signal circuit center conductor.

B125B 04

The radio detects an open in the antenna 2 signal circuit center conductor.

Action Taken When the DTC Sets

Radio reception may be poor or not available.

Conditions for Clearing the DTC

• The condition responsible for setting the DTC no longer exists.
• A history DTC will clears after 50 consecutive malfunction-free ignition cycles have occurred.

Diagnostic Aids

Poor AM and FM radio reception may be due to multiple influences, some of which may not be vehicle related. Areas which have high RF traffic or block the signal path may cause a degradation in radio reception. Radio reception may also be influenced by items within the vehicle, but not part of the radio system. Such examples are aftermarket electrical accessories or other items which may generate noise in the vehicle electrical system. Aftermarket window tinting, especially when there is a metallic in the film, may reduce radio reception.

Reference Information

Schematic Reference

Radio/Navigation System Wiring Schematics (IOB) , Radio/Navigation System Wiring Schematics (IOR) or Radio/Navigation System Wiring Schematics (IO5/IO6) , or Radio/Navigation System Wiring Schematics (IOS/IOT).

Connector End View Reference

Component Connector End View Index

Description and Operation

Radio/Audio System Description and Operation (IO6) , Radio/Audio System Description and Operation (IOB) , or Radio/Audio System Description and Operation (IOS/IOT/IOU).

Electrical Information Reference

• Refer to Circuit Testing
• Refer to Connector Repairs
• Refer to Testing for Intermittent Conditions and Poor Connections
• Refer to Wiring Repairs

Scan Tool Reference

Control Module References for scan tool information.

Circuit/System Verification

1. Ignition ON, A11 radio ON.

2. Verify station reception is normal when tuned to several known good FM stations.

• If FM reception is poor.

Refer to Circuit/System Testing

• Go to next step: If reception is normal.

3. Verify DTC B125B is not set as current.

• If DTC B125B is set as current.

Refer to Circuit/System Testing

• I Go to next step: f DTC B125B is not set as current.

4. All OK.

Circuit/System Testing

Quarter Window Antenna

1. Ignition OFF, disconnect the radio antenna coax cable from the A11 radio and from the T23L Radio Antenna Amplifier.

2. Verify the antenna coax cable passes the coax cable component test. Refer to Component Testing.

• If the coax cable does not pass the test.

Replace the antenna coax cable.

• Go to next step: If the coax cable passes the test.

3. Connect the antenna coax cable to the A11 radio. Ignition ON, A11 radio ON.

4. Verify a test lamp illuminates between the antenna coax cable center terminal and ground at the T23L Radio Antenna Amplifier connector.

• If the test lamp does not illuminate.

Replace the A11 radio.

• Go to next step: If the test lamp illuminates.

5. Test or replace the T23L Radio Antenna Amplifier.

Rear Window Antenna

1. Ignition OFF, disconnect the radio antenna coax cable from the A11 radio and from the T23R Radio Antenna Amplifier.

2. Verify the antenna coax cable passes the coax cable component test. Refer to Component Testing.

• If the coax cable does not pass the test.

Replace the antenna coax cable.

• Go to next step: If the coax cable passes the test.

3. Connect the antenna coax cable to the A11 radio. Ignition ON, A11 radio ON.

4. Verify a test lamp illuminates between the antenna coax cable center terminal and ground at the T23R Radio Antenna Amplifier connector.

• If the test lamp does not illuminate.

Replace the A11 radio.

• Go to next step: If the test lamp illuminates.

5. Test or replace the T23R Radio Antenna Amplifier.

Component Testing

CAUTION: Refer to Test Probe Caution.

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.

To prevent false reading when testing the center coax terminals, use care not to ground the test probe on the outer housing/shield.

Coax Cable Test

1. Ignition OFF, disconnect the coax cable at both components.

2. Test for less than 5 Ω between coax cable center terminal end to end.

• If 5 Ω or greater

Replace the coax cable

• Go to next step: If less than 5 Ω

3. Test for less than 5 Ω between the coax cable outer shield end to end.

• If 5 Ω or greater

Replace the coax cable

• Go to next step: If less than 5 Ω

4. Test for infinite resistance between the coax cable center terminal and the coax cable outer shield.

• If less than infinite resistance

Replace the coax cable

• Go to next step: If infinite resistance

5. All OK

Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair.

• Refer to Radio Antenna Amplifier Replacement
• Refer to Control Module References for radio replacement, programming, and setup.

READ NEXT: