B125A
DTC B125A
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis Strategy Based Diagnosis for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions Diagnostic Procedure Instructions provides an overview of each diagnostic category.
DTC Descriptors
DTC B125A 02
- Antenna Signal Circuit Short to Ground
DTC B125A 04
- Antenna Signal Circuit Open Circuit
Diagnostic Fault Information
Circuit/System Description
Active Antenna (U77)
The active antenna system uses an integral antenna applied as an appliqué to the rear glass. The antenna module receives both AM and FM 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, both AM and FM signals are amplified.
Spoiler Antenna (UB3)
The radio antenna is integral to the spoiler on the rear decklid. The antenna module on the underside of the spoiler receives both AM and FM signals from the antenna. The radio antenna module is enabled when the radio is turned on. The radio provides battery voltage to the antenna module using the remote enable circuit. When a 12 V signal is seen by the antenna module on the remote enable circuit, both AM and FM signals are amplified.
Conditions for Running the DTC
* Ignition ON.
* Battery voltage must be between 9-16 V.
Conditions for Setting the DTC
B125A 02
The radio detects a short to ground in the antenna signal circuit center conductor.
B125A 04
The radio detects an open in the antenna 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.
AM reception is highly dependent on the antenna module receiving battery voltage from the radio and being properly grounded. The antenna module has a built in antenna amplifier that boosts both AM and FM reception. When the antenna module does not receive power, AM stations may not be received and FM reception will be limited. If the module is not properly grounded, excessive interference in the signal may occur, or reception may be limited.
Reference Information
Schematic Reference
Radio/Navigation System Schematics Radio/Navigation System Schematics
Connector End View Reference
Component Connector End Views Fuel Pump and Level Sensor Assembly - Primary
Description and Operation
Radio/Audio System Description and Operation Radio/Audio System
Electrical Information Reference
* Circuit Testing Circuit Testing
* Connector Repairs Connector Repairs
* Testing for Intermittent Conditions and Poor Connections Testing for Intermittent Conditions and Poor Connections
* Wiring Repairs Wiring Repairs
Scan Tool Reference
Control Module References 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 AM and FM stations.
• If AM or FM reception is poor.
Refer to Circuit/System Testing
• If reception is normal
3. All OK.
Circuit/System Testing
Active Antenna (U77)
1. Ignition OFF, disconnect the radio antenna coax cable from the A11 radio and from the K46 radio antenna module.
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
• 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 K46 radio antenna module connector.
• If the test lamp does not illuminate
Replace the A11 radio.
• If the test lamp illuminates
5. Test or replace the K46 radio antenna module.
Spoiler Antenna (UB3)
1. Ignition OFF, disconnect the radio antenna coax cable from the A11 radio and the K46 radio antenna module.
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
• If the coax cable passes the test
3. Disconnect the harness connector at the K46 radio antenna module. Ignition ON, A11 radio ON.
4. Verify a test lamp illuminates between the control circuit terminal A and ground.
• If the test lamp does not illuminate
1. Vehicle OFF. Disconnect the X1 harness at the A11 radio.
2. Test for less than 2 ohms in the control circuit end to end.
• If 2 ohms or greater, repair the open/high resistance in the circuit.
• If less than 2 ohms, replace the A11 radio.
• If the test lamp illuminates
5. Test or replace the K46 radio antenna module.
Component Testing
Caution: Refer to Test Probe Caution 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 ohms between coax cable center terminal end to end.
• If 5 ohms or greater
Replace the coax cable
• If less than 5 ohms
3. Test for less than 5 ohms between the coax cable outer shield end to end.
• If 5 ohms or greater
Replace the coax cable
• If less than 5 ohms
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
• If infinite resistance
5. All OK
Repair Instructions
Perform the Diagnostic Repair Verification Verification Tests after completing the repair.
* Radio Antenna Module Replacement (Coupe) Radio Antenna Module Replacement (Coupe)
* Control Module References Control Module References for radio replacement, programming, and setup.