Buick Regal Owners & Service Manuals

Buick Regal: DTC B124B (IO5/IO6)

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 Descriptor

DTC B124B

USB 1 Circuit

For symptom byte information refer to Symptom Byte List.

Diagnostic Fault Information

Cellular, Entertainment, and Navigation

1. SD Card reader and USB port Inoperative.
2. No left side audio from device connected to AUX jack.
3. No right side audio from device connected to AUX jack.
4. Noticeable distortion may be present in affected audio channel.
5. Fault may affect one or more components, dependent on fault location.
6. Fault affects multiple components, dependent on vehicle equipment.
7. Radio does not detect auxiliary device connection, AUX not available as input selection.
8. AUX always available as an input selection, with or without auxiliary device connected.

Circuit/System Description

The infotainment system has a USB port and SD card reader slot located in the center console. The USB port and the card reader slot interface with a hub device, internal to the auxiliary jack, USB, and memory card receptacle assembly. The auxiliary jack, USB, and memory card receptacle assembly receives fused battery voltage and ground from the harness to power the internal hub device as well as providing additional amperage to power USB devices.

The internal hub device interfaces directly with the human machine interface control module via a standard USB cable. A Mini type USB connector is used to connect the cable at the USB port and at the human machine interface control module and at the auxiliary jack, USB, and memory card receptacle.

Standard USB male to female connections are typically used for connecting USB cables together where an in-line connection is required. An in-line cable connection is typically found between the console and I/P harness.

USB Port

The USB port allows connectivity to the infotainment system from portable media players or a USB storage device (memory stick/ flash drive). When a device is connected to the USB port, the system detects the device and switches to USB as the audio source. Once connected, the device can be controlled from the radio controls.

Not all portable media player devices or file types are compatible. Refer to the vehicle owner's manual for information on USB devices, control, and operation.

SD Card Reader

The infotainment uses the SD card reader as a mass storage device, similar to a USB storage device.

Refer to the owners manual for information on media types supported via the SD card reader.

Conditions for Running the DTC

  • Ignition is ON or in the ACC position
  • The system voltage is 9-16 V
  • The infotainment system is ON
  • The test is run once per second when the infotainment system is operating

Conditions for Setting the DTC

B124B 0B

The human machine interface control module detects an excessive current condition on the USB 5 V circuit.

B124B 04

The human machine interface control module does not detect the vehicle hub device.

B124B 11

The human machine interface control module detects an additional hub device attached to the vehicle USB port.

Action Taken When the DTC Sets

The USB port and SD card reader are inoperative while the DTC is current.

Conditions for Clearing the DTC

  • The condition for setting the DTC is no longer present.
  • A history DTC will clear once 50 consecutive malfunction-free ignition cycles have occurred.

Diagnostic Aids

  • This DTC may be set due to the connection of an incompatible or faulty USB device.
  • The human machine interface control module has two available USB connections. The human machine interface control module calibrations determine what is expected to be connected to each of these connection: either a USB port or a USB/SD Card reader HUB. USB 1 and USB 2 refers to the connector at the module that the port or hub is connected to.

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.

Special Tools

  • EL-50334-20 Multi-Media Interface Tester (MIT)
  • EL-50334-50 USB Cable and Adapter Kit
  • EL-50334-14 Infotainment Test Cable

Circuit/System Verification

1. Verify DTC B124B is not set. Since occurrences of this DTC can be caused by an incompatible or faulty USB device, review with the customer the conditions under which their concern occurred.

  • If DTC B124B is set.

Refer to Circuit/System Testing.

  • Go to next step: If DTC B124B is not set.

2. Ignition ON, infotainment system ON.

3. Connect the EL-50334-20 Multi-Media Interface Tester (MIT) to the X83 Auxiliary Audio Input USB port and select the USB test mode.

4. Verify the audio from the EL-50334-20 Multi-Media Interface Tester (MIT) is heard through the infotainment system while operating the system to play audio from the test tool.

  • If audio is not heard from the test tool
  1. Insert an SD card with compatible media into the SD card slot.
  2. Verify the media on the SD card can be accessed while operating the system to connect to the SD card.
    • If the SD card reader cannot be accessed, refer to Circuit/System Testing.
    • If the SD card reader can be accessed, replace the X83 Auxiliary Audio Input.
  • Go to next step: If audio is heard from the test tool

5. Insert an SD card with compatible media into the SD card slot.

6. Verify the media on the SD card can be accessed while operating the system to connect to the SD card.

  • If the SD card reader media cannot be accessed

Refer to Circuit/System Testing

  • Go to next step: If the SD card reader media can be accessed

7. All OK.

Circuit/System Testing

1. Ignition OFF, disconnect the X1 harness connector at the X83 Auxiliary Audio Input.

2. Test for less than 10 Ω between the ground circuit terminal 4 and ground.

  • If 10 Ω or greater
  1. Ignition OFF.
  2. Test for less than 2 Ω in the ground circuit end to end.
    • If 2 Ω or greater, repair the open/high resistance in the circuit.
    • If less than 2 Ω, repair the open/high resistance in the ground connection.
  • Go to next step: If less than 10 Ω

3. Verify that a test lamp illuminates between the B+ circuit terminal 6 and ground.

  • If the test lamp does not illuminate
  1. Ignition OFF, remove the test lamp.
  2. Test for less than 2 Ω in the B+ circuit end to end.
    • If 2 Ω or greater, repair the open/high resistance in the circuit.
  • Go to next step: If the test lamp illuminates

4. Verify the USB cable is properly connected at all components and in-line connections, and there is no damage to the cable or connections.

  • If connection problems or cable damage is noted.

Perform the appropriate repair or replacement to correct any issues.

  • Go to next step: If no connection problems or cable damage is noted.

5. Connect the X1 harness connector at the X83 Auxiliary Audio Input.

6. Disconnect the vehicle USB cable X4 harness connector at the K74 Human Machine Interface Control Module and the X83 Auxiliary Audio Input.

7. Connect the EL-50034 - 14 Infotainment Test Cable and the EL-50334 - 2 Type-A Female to Mini-B Male Cable together. Connect the assembled test cable to the K74 Human Machine Interface Control Module and the X83 Auxiliary Audio Input.

8. Ignition ON, infotainment system ON.

9. Connect the EL-50334-20 Multi-Media Interface Tester (MIT) to the X83 Auxiliary Audio Input USB port and select the USB test mode.

10. Verify the audio from the EL-50334-20 Multi-Media Interface Tester (MIT) is heard through the infotainment system while operating the system to play audio from the test tool.

  • If audio is not heard from the test tool
  1. Replace the X83 Auxiliary Audio Input. Connect all harness connectors.
  2. Connect the EL-50334-20 Multi-Media Interface Tester (MIT) to the X83 Auxiliary Audio Input USB port and select the USB test mode.
  3. Verify the audio from the EL-50334-20 Multi-Media Interface Tester (MIT) is heard through the infotainment system while operating the system to play audio from the test tool.
    • If audio is not heard from the test tool, replace the K74 Human Machine Interface Control Module.
    • Go to next step: If audio is heard from the test tool.
  4. All OK.
  • Go to next step: If audio is heard from the test tool

11. Connect the vehicle USB cable X4 harness connector at the K74 Human Machine Interface Control Module.

12. Disconnect the console to I/P USB in-line connector. Connect the assembled test cable to the I/P side of the in-line USB cable connector and the X83 Auxiliary Audio Input.

13. Connect the EL-50334-20 Multi-Media Interface Tester (MIT) to the X83 Auxiliary Audio Input USB port and select the USB test mode.

14. Verify the audio from the EL-50334-20 Multi-Media Interface Tester (MIT) is heard through the infotainment system while operating the system to play audio from the test tool.

  • If audio is not heard from the test tool

Replace the I/P USB cable assembly.

  • Go to next step: If audio is heard from the test tool

15. Replace the console USB cable assembly.

Repair Instructions

  • Refer to Audio Disc Player and USB Receptacle Replacement
  • Refer to Control Module References for human machine interface control module replacement, programming, and setup.
  • Perform the Diagnostic Repair Verification after completing the repair.

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