We tried to automate most of the things for you, but still there are situations that require some undrestanding. Check below.

Installation and Base Usage

What are the two EXT ports for?

The extension (EXT1 and EXT2) ports allow you to connect optional accessories, such as GROM Bluetooth Dongle, GROM Auxiliary 3.5mm harness, or HD Radio Dongle.
GROM Extension cable connections

How do I switch between USB and EXT ports (AUX/Bluetooth/HD Radio)?

There is no need to switch to Bluetooth. As long as Bluetooth connection is active, such as phone call comes in, or the music streaming is on, it will override currently playing mode (USB/AUX/HD radio).
To switch MODES, switch to CDC (GROM mode)
1. Press FM (or AM), wait for 1 second.
2. Press CD/MODE/DISC (to access GROM mode). You should hear announce of the currently active mode.
3. Immediately press > (next track button).
4. Voice will announce the mode (RADIO or AUX). If mode is not desired, repeat #3
5. Wait for 2 seconds for selected mode to become active
6. The ports are labeled audibly as USB=USB EXT1=RADIO (for HD Radio), EXT2=AUX
If HD Radio Dongle is not present the GROM will skip "RADIO" mode and will announce "AUX" right after "USB"
Refer to the video on how to switch the Modes on GROM-USB or GROM-MST4 device for better understanding.

To use Bluetooth, does GROM need to be in the AUX mode?

No, it does not matter what mode is GROM in. As soon as Bluetooth is used (such as for hands free phone call or wireless audio), it will override any previously active mode.


How many root folders/virtual playlists I can set up on my USB stick?

You can set up up to 6 folders/virtual playlists.
We recommend using smaller drives with manageable number of folders ~20 and change them. GROM will remember 4 sticks and will be able to restore all positions in up to 20 folders for them all.

How many files per root folder (playlist)?

We have tested with ~1000 files in a playlist. So technically no limits but be aware that it might take longer to switch between tracks and proper track ordering may not be possible.

What formats/bitrates it supports ?

  • MP3 layer 1,2,3 bitrate up to 320Kbps
  • WMA (no DRM) bitrate up to 384Kbps
  • AAC/MP4/iTunes+ (no DRM). Bitrate up to 384Kbps
  • OGG/Vorbis bitrate up to 384Kbps
  • FLAC Lossless
  • What limits does GROM-MST4 have?

  • Positions preserved for 4 different USB sticks
  • Positions preserved for 20 playlists per USB stick
  • Random will work for 2000 files only, the rest may not shuffle properly or repeat during play
  • Can GROM-MST4 power up my portable HDD?

    Yes. It is able to provide steady 1A @ 5V which is enough for the most portable hard drives

    Can GROM-MST4 charge my iPhone or Android phone?

    Yes. It is able to provide steady 1A @ 5V which is enough charge the iPhone. It will also charge the Android phone, but at the slower speed of 0.5amp

    How can I connect iPod/iPhone/iPad to GROM-MST4 system?

    iPod/iPhone/iPad can be connected using standard USB to iPhone cable. The GROM supports Lightning style and 30-pin connector style cables.
    You can also connect your iPod/iPhone/iPad using GROM AUX and 5V USB charging cable Check our store or add to your cart along with GROM-MST4 module.
    You can also connect your iPod/iPhone/iPad using GROM Bluetooth Dongle for wireless music streaming and hands free phone calls. Check our store or add to your cart along with GROM-MST4 module.

    How many tracks device support?

    USB2 has been tested with ~10000 tracks on a drive (~80GB) with 20 playlists (root folders)
    All supported stereos are not able to show the track number larger than 99. It is normal and will not affect the track currently playing. In case if you play track 1467, the stereo will show Track# 67

    Should I name folders in certain way and place all files into the same folder ?

    No. We do not recommend using 1 directory for all your files. It will make it hard to preserve the file sequence.
    It is better to organize your music like: Playlist -> Artist -> Album as shown below
    Folder "01-Mine" will be mapped to the first DISK and all files inside directory "Extreme Behavior" will play in ascending order (01, 02, 03 etc) and will not mix up with any other album.

    I see that device supports CONFIG file. What is it ?

    Config file functionality allow to remap some buttons or adjust behavior of the device. More information is available here

    Audio tracks are not sorted and play out of order

    In order to have your files organized you can either add number in front of the file name or use this sorting utility. Just place EXE file in the root of the stick and run. More information available here:here


    There is no audio comes out when I use aux cable

    Make sure that you are in correct mode. You can connect the aux cable into EXT1 or EXT2. If you connected the aux cable into EXT1, your GROM should be in the AUX mode. If you connected the aux cable into the EXT2 port, the GROM should be in the iPod mode.

    Tracks play not in order

    Make sure you name tracks as shown below. Check that you have no gaps in numbering and numbering starts with 1 (not 0!)
    You can use formats like: "01." or "01-" or "01 "

    Some tracks are not playing, some duplicate

    Make sure that tracks have no gaps in numbering. And either all tracks have numbers or none. In example below the underlined track will not play and the circled one will play twice (as 2nd and 4th).

    Some folders are not playing, some skip

    If you need folders to be assigned to a particular disk, they have to be named as shown below. Make sure root folders (playlists) are named in latin characters with no spaces in names !

    Firmware update does not seem to happen

    If you do not have any issues with the unit do NOT update !
    In some rare cases when update process failed GROM goes into corrupt mode. You will need to disconnect the unit from the main harness or remove the car stereo fuse

    Update "bricked" the unit

    Double check that you applied the right firmware to the unit. If you apply Mazda firmware to your Toyota (for ex.) it will disable the device and you will need to apply the right update after you recycle power for GROM-USB2 box
    Then do the following steps:
    - Save the latest firmware for your car make on a stick formatted FAT/FAT32
    - Make sure you name the file as gromusb2.hex and it resides in the root
    - Disconnect the GROM box from white harness
    - Attach USB stick with latest firmware to the GROM box
    - Attach the GROM box to the white harness
    - The led on USB should blink 1-2 seconds and then become solid or go off
    - Turn on ignition and switch over to GROM (SAT/CD changer) !

    External audio player does not produce good sound through 3.5mm jack

    Make sure you switch GROM box into AUX mode

    On my radio MIX/RND mode will not allow to advance tracks in random order

    This is stereo limitation. Turn the MIX/RND mode on and let the track advance in random order upon track completion

    While in AUX mode I hear background noise and whine

    It is normal when the other end of AUX cable is _not_ connected to anything. Once iPod or MP3 player connected there will be no noise or whine. If noise still present after the audio source is connected then contact Technical support.

    I am not sure if firmware update did go through

    832-12-****** units: To check firmware version switch to USB mode. Remove USB stick. The track number will show build number.
    Please note: Build number displayed will NOT match the firmware version that is displayed on download page. So in order to see if firmware changed do this operation before and after update !
    834-13-****** units: To check firmware version switch to USB mode. Remove USB stick. The track number will show VERSION number.
    Please note: Build number displayed WILL match the firmware version that is displayed on download page

    GROM box is recognized by stereo but do not play from USB. Only shows CD 1-01

    GROM is in AUXILIARY or IPOD mode. To switch to USB you should:
    1. Press FM (or AM), wait for 1 second.
    2. Press CD/MODE/DISC. You should hear announce.
    3. Immediately press > (next track button).
    4. Announce should say "USB". If not, repeat step 3
    5. Wait for 2 seconds for USB to start playing.

    USB playback is screwed, playing some files, skipping directories, etc

    If you are using USB extension cable, try to connect your stick directly to the GROM box and test again
    Make sure the USB stick is formatted with FAT32. Use full format in Windows desired.

    ID3 tags on MP3 files cannot be seen

    Make sure all tags are ASCII encoded. Some tools like Windows Media Player use Unicode which makes it unreadable on most stereos.
    To make sure you sync all ID3 tags properly you may use the following utility

    Music is not playing with AALinQ on Android phone and USB Kit

    If the version of your Android software is 2.3 and newer, you will need to have USB Debugging disabled (off) to allow AALinQ to communicate between your Android and the GROM-USB2P. If the version of your Android software is older than 2.3, you will need to enable USB Debugging function on your phone.
    To enable/disable USB Debugging, on Android device go to


    USB Audio Streaming on Jelly Bean and up Android phones, without AALinQ

    USB Audio streaming (without AALinQ) is supported as long as Android phone is running Android 4.1 and above. Most but not all Android 4.1+ phone support USB streaming due to the way some phone companies leaving this feature out in their version of Android.
    You will have to enable USB streaming using a config file. Check the instructions on the forum.
    With the config file loaded, any application on the phone (i.e. Pandora, Spotify, Navigation, etc.) will have its audio redirected through the GROM in clean digital audio. There will be no track control though with any of these application also if stereo supports text, song info will not not be displayed (on AALinQ the text is supported.)
    Please note that with the USB streaming config file loaded AALinQ will work just like other applications with no track control or song info. If you would like to re-enable the AAlinQ controls and text, you will have to either reset the GROM unit by pulling white connector to disconnect power from it or load another config file to turn it back on which would be config file with gromusb2.cfg with a= 1 instead.
    Known limitations are: HTC phones are not supporting USB Audio streaming. Other phones, including Samsung and Nexus Android phones, do support USB streaming.
    Check demo video for Android USB streaming at GROM Youtube channel

    Jelly Bean Style Skin on AALinQ player

    To add Jelly Bean style skin on your AALinQ player, do the following:
    Download the AALinQ Jelly Bean Style Skin at Google Play
    Open AALinQ Media Player on your phone
    Go to Settings --> Current skin
    Choose AALinQ Jelly Bean skin


    Can I activate iPhone Siri voice control?

    You can activate Siri voice control by pressing Scan button twice.
    Please note that your phone should not be in Bluetooth audio streaming mode.


    I cannot pair the phone with the GROM with BT option

    1. Please make sure the latest firmware installed
    2. Turn the car off. Wait 30 seconds
    3. Turn the car on. Now your phone should see the GROM-CAR device. Note that your stereo may be in any mode (FM, AM, CD, SAT etc)
    4. Also note that GROM-CAR will be discoverable 3 minutes and if you do not pair the phone you have to repeat items 2-3 again
    5. Follow your phone manual and pair it with GROM-CAR
    Now the pairing is done and after each ignition start your phone will automatically connect to GROM-CAR!

    GROM-CAR is visible but when trying to pair or connect I get an error

    BTD module may go into corrupt mode. Do the following sequence:
    1. Enable mode switching state (GROM-FM-GROM)
    2. Once voice announcing the mode is heard press SCAN button
    3. There should be voice beep confirming full reset
    You should be able to select and connect to GROM-CAR now

    Does bluetooth remember multiple devices? How does it auto connect to one when the car is turned on?

    The GROM Bluetooth is capable of pairing up to only 2 devices at a time. It can only connect to one Paired device at a time. It will auto connect to the phone that is nearby when the vehicle is started.

    The car came with Bluetooth phone capability but no streaming audio capability. If I hook up the GROM Bluetooth can I use it for the A2DP streaming only, and use the car Bluetooth for hands free calls?

    If you have newer smartphone, you should be able to select which paired device will handle phone calls and which will handle music streaming. This is all typically done from the phone Bluetooth settings, and available in iPhone and Android phones.

    The phone and GROM syncs at times and on other occasions it will not stream audio.

    After first turning on stereo/GROM please give the GROM 10-15 seconds to fully sync with bluetooth before hitting play on device.

    My phone is connected to GROM Bluetooth, but there is no sound coming from the speakers.

    Make sure that the Bluetooth volume is turned on and all the way up.