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By YOUCANIC on May 24, 2019

Troubleshoot BMW Radio Sound Problems

BMW vehicles may suffer from problems such as no sound, iDrive not turning on and even cracking sound from the speakers. In this guide, we take a look at 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 complexity of the BMW entertainment system, many car mechanics are not familiar or know how to fix 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 BMW radio setup

MOST stands for Media Oriented Systems Transport and can connect up to 64 bus systems in BMW vehicles in a ring configuration. Because BMW audio components are configured in a loop, if one module fails, everything stops working. MOST networks connect multiple devices such as the amplifier, telephone unit, satellite tuner, iPod interface, and Bluetooth handsfree module and so on.

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 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 left side of the trunk or behind the rear seat.
  • Headset interface - Located left side of the trunk. 

Common Symptoms 

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 issue SVS or TCU module
  • iDrive keep switching to the home screen

Common Problems

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 problem 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 going on with your BMW audio system.  If you are getting the SOS malfunction on startup it can be because the telephone module is recognizing 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

Troubleshoot BMW Audio Problems DIY

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

Disconnect battery

bmw battery in trunk

Disconnecting the car battery for at least 12 hours will sometimes reset the failed MOST component and fix the problem. 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 is showing PRESENT status the problem needs to be fixed before the code can be cleared. If your BMW has no sound or doesn't power at all, there typically is 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. 

Instructions

  1. Plug in 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 Control Units menu. bmw MOST control unit module reading codes

     

  4. Select 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 one of the modules 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 the 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 and you can live without it.

How to find a defective module

  1. Locate the MOST components in 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 considering the fact that they need to be programmed as well. A cheaper alternative is to repair your unit. There are many services that 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 BMW car? 

In which cars can I used 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

Additional Resources

  1. Avin M.O.S.T Interface: Install Any Aftermarket Radio To BMW Logic 7 by 346source on Youtube
  2. Understanding BMW MOST BUS System 
  3. Resource - MOST bus fault patterns by BMW Tech on Bimmerforums
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