Is there no sound on your BMW speakers? Learn how to fix it by following the procedures below. BMW vehicles may suffer from problems such as no sound from speakers, iDrive not turning on, and even cracking sound from the speakers. 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.

Understanding the BMW radio setup

MOST, 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. The Bluetooth module sometimes causes this. 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 usually points to an issue with the radio or telephone module.
  • CIC / CCC
    If your BMW is not turning on, there is a good chance the CIC/CCC head unit is defective and needs to be replaced.



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

bmw service engine soon diagnose

If you are experiencing problems, reading fault codes from the MOST module is a good starting point. Run a full system scan on the vehicle. 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, a fault code will typically be stored in the MOST module. Scanners that read and clear BMW MOST fault codes include YOUCANIC Full System Scanner. 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
  4. Select the MOST Module.

Once you enter the MOST module, you can 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.


The 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 passes through each module simultaneously, including an amplifier, ask unit, amplifiers, tuner, Bluetooth phone, etc.

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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 on the trunk’s left side.

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 installing 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 module 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 must be programmed. A cheaper alternative is to repair your unit. Many services will fix your defective unit for a fraction of the dealer’s price.


There could be several reasons why the radio in a BMW is not producing sound. Some possible technical causes include a malfunctioning amplifier, a problem with the speakers, a blown fuse, or an issue with the radio’s power supply. Additionally, the problem could be caused by a malfunctioning head unit (CIC or CCC), which is the component that houses the radio and controls its functions. If the radio is not producing sound, it is recommended to check the fuse and ensure it is not blown. If the fuse is fine, then it is recommended to check the wiring and connections to ensure that they are secure. If the problem persists, it is recommended to take the vehicle to a BMW dealership or a professional car audio technician for further diagnosis and repair.

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

How much does it cost to fix a radio in a BMW?

Around $200 – $600.

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  1. 2004 BMW x3 the radio swithes on. When the ignition is on position one the sounds comes from the speakers, but when the car is started the radio switches on but there is no sounds.

  2. When i try to close the windows and turn the steering wheel at max the audio goes down like it has low power

  3. Anonymous says:

    My recently acquired 06 325 xi has the stereo unit illustrated in this photo. CD located above a single knob tuner with presets below display and DVD player in the bottom. I am not getting any sound from alarms , radio, or cd player, but all appear to be working on the I drive display screen, including the CD track monitor and timer. The MOST connection looks complete throughout the system, but does not appear to be routed thru the on board Leer amplifier. The amplifier is receiving 12.6 volts, but has some sort of paint stick letters that seems to indicate it was replaced somewhere along the line. Can you tell me if this is the correct amp for this system or if it requires coding after a replacement was installed?

  4. Anonymous says:

    Huge thanks for a really great article. I’m not sure if it relates precisely to my situation because I own a 2008 328i e90 with really bad static noise issues (even when the car is turned off). It happens whenever the OEM (Lear PL2) amp is connected to the ISO connector in the trunk. Do you have any additional advice which might help me track down the problem?

  5. Anonymous says:

    Great article, just wanted to say thanks! I also wanted to mention that the standard MOST loop most sellers on Amazon sell used to bypass components does NOT fit without modification (you have to cut it up or tear off the sides of the plastic to get it to fit the optical connection on the car) The one i bought came pre-trimmed so it fits anywhere it needs to be used with no hassle at all:

    This video on YouTube was also very helpful in finding the proper component to bypass: I hope this helps the next guy!