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BMW vehicles may suffer from problems such as no sound from speakers, iDrive not turning on, and even cracking sound from the speakers.

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This guide explains how to troubleshoot BMW radio issues yourself.

Getting your BMW radio and sound system diagnosed by the dealer can be very expensive. Due to the BMW entertainment system's complexity, many car mechanics do not know how to fix the BMW radio problem unless they specialize in BMWs.

This article is meant to help BMW owners and mechanics who are trying to fix BMW radio issues.

Understanding the BMW radio setup

MOST, which stands for Media Oriented Systems Transport, can connect up to 64 bus systems in BMW vehicles in a ring configuration.

The BMW audio components are configured in a loop, so if one fails, everything stops working. Multiple devices, such as the amplifier, telephone, satellite tuner, iPod interface, Bluetooth hands-free module, etc., are connected to MOST networks.

Advantages of MOST Bust network

  • Simplification of wiring,
  • Reduction in the number of cables needed
  • Transmission of complex data
  • Flexible configuration

MOST Components

This is a list of components that can be part of the BMW MOST network. Your BMW will have a few of these, depending on the options that came with your car.

You may have anywhere from three up to eight components.

  • CIC / CCC - Located in the dashboard, below the climate control
  • CD Changer - Integrated with the CIC/CCC or in the glovebox.
  • Telephone - In the trunk, left.
  • Amplifier Logic 7 - In the trunk, left.
  • Satellite DLP Module - In the trunk, left side.
  • Bluetooth Phone Module - In the trunk, left side.
  • SPS Speech Module - Located in the trunk, left side
  • Voice Input Control Unit SVS - In the trunk, left side.
  • ASk Head unit - Head unit in the dashboard
  • TCU telematics control unit - In the trunk, left side.
  • Antenna tuner or digital tuner - Located on the left side of the trunk or behind the rear seat.
  • Headset interface - Located left side of the trunk.


Here are a few symptoms you may notice if one of the MOST components fails.

  • Malfunction message on the iDrive screen
  • BMW radio works but has NO sound audio
  • SOS malfunction error on startup
  • Bluetooth phone not working
  • Crackling From Speakers could be an issue SVS or TCU module
  • iDrive keep switching to the home screen

Common Issues

Possible problems that can trigger fault codes in the MOST module.

  • BMW Radio Works but NO Sound  This problem is caused when the optical loop is broken. Even though all the modules function and seem to work properly, one of the modules listed above is defective or not turning on. To find out which module is defective, you can use a female fiber optic loop (also called a lollipop) and bypass all the modules one at a time. When you bypass the defective module, you will get sound from your BMW speakers. The telematics unit and the speed module located in the trunk are often the culprits.
  • Cracking from speakers A common problem is cracking, usually from the front speakers. The iDrive may also randomly restart and go to the home screen. This is sometimes caused by the Bluetooth module. Try performing a MOST reset.
  • SOS malfunction on startup The airbag or SOS light comes on when there is a problem with your BMW audio system. If you are getting the SOS malfunction on startup, it can be because the telephone module recognizes that you won't be able to make a phone call in case of an emergency. You can scan the airbag (SRS) module to verify the fault code. The code will usually point to an issue with the radio or telephone module.
  • CIC / CCC If your BMW is not turning on at all, there is a good chance the CIC/CCC head unit is defective and needs to be replaced. Learn more about BMW iDrive radio won't turn on issue.

Troubleshooting Tips

bmw battery in trunk

Here are a few troubleshooting steps you can follow if you are experiencing problems with your BMW radio and audio system.

Disconnect Battery

Disconnecting the car battery for at least twelve hours will sometimes reset the failed MOST component and fix it. Leave the battery disconnected overnight.

This will force the components to reboot. Another way to reset BMW MOST is by using a BMW diagnostic scanner.

Read Fault Codes

If you are experiencing problems, a good starting point is to read fault codes from the MOST module.

If any code shows PRESENT status, the problem needs to be fixed before the code can be cleared. If your BMW has no sound or power, there will typically be a fault code stored in the MOST module.

List of scanners that read and clear BMW MOST fault codes.

These are only a few examples. Many diagnostic scanners allow you to read and clear BMW MOST fault codes. To learn about OBD2 scanners that work on BMWs, check the article on Choosing the best OBD2 scanner for BMW.


  1. Plugin the OBD-II scanner into the diagnostic port under the dashboard.diagnose bmw MOST fault code via obd2 port
  2. Turn on the ignition; don't start the engine.turn on bmw ignition to read MOST fault codes
  3. Turn on the scanner and select your BMW chassis. Next, Select the Control Units MOST control unit module reading codes
  4. Select the MOST Module.
  5. Once you enter the MOST module, you will be able to do the following.
    • Read Codes from MOST Module
    • Clear Codes from MOST Module
    • Perform Adaptations, Activations, Tests

BYPASS using Fiber Optic Loop

You can also diagnose BMW radio problems using a Fiber Optic Loop.

bmw fiber optic loopThe MOST BUS signal (red light that flashes in the fiber optic cable) generates from the head unit, which will be your NBT, CIC, or CCC unit.

The signal passed through each module one at a time, including an amplifier, ask unit, amplifiers, tuner, Bluetooth phone, etc.

To find out which unit is the culprit, you can use a female fiber optic loop to bypass each component one at a time.

When you bypass the defective module, the sound should be back. Most of the BMW audio modules are located on the left side of the trunk.

If the defective component is critical, you will need to replace the module or get it repaired. Unless the defective module is not critical, such as a CD changer, you can live without it.

How to find a defective module

  1. Locate the MOST components on the left side of the trunk. You will be unplugging the fiber optic cable from one unit at a time and install a female bypass loop. Start by passing the telephone unit.
  2. Turn on the radio and check if the radio is working and if you have sound.
  3. If the first module you bypassed didn't fix the problem, reinstall the fiber optic cable and go to the next module. Disconnect each of the modules one at a time and install the bypass loop. When the head unit (radio) starts working, you have identified the failed unit.

Replacing BMW audio units can be very expensive because they need to be programmed as well. A cheaper alternative is to repair your unit.

Many services will fix your defective unit for a fraction of the dealer price.

BMW Audio Control Unit Repair Services

Frequently Asked Questions

Can I install an aftermarket on the BMW car?

  • Use a BMW MOST Fiber Optic Amp Interface. It is possible to keep the factory speakers, amplifier, and even subwoofer working with an aftermarket radio.

In which cars can I use a MOST fiber optic interface?

  • You can install an aftermarket radio on any BMW. Some examples include E90, E91, E92, E93, E60, E61, E81, E82, E83, E84, E70, E87, E88, E89