GROM-MST4 FAQ

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.

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.

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.

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.

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.

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

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

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

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 500mA

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.

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

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 belowFolder "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.

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.

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 "

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).

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 !

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

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 boxThen 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) !

Make sure you switch GROM box into AUX mode

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

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.

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 is in AUXILIARY or IPOD mode. To switch to USB you should:

Press FM (or AM), wait for 1 second.

Press CD/MODE/DISC. You should hear announce.

Immediately press > (next track button).

Announce should say "USB". If not, repeat step 3

Wait for 2 seconds for USB to start playing.

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.

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

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

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

Please make sure the latest firmware installed

Turn the car off. Wait 30 seconds

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)

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

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!

BTD module may go into corrupt mode. Do the following sequence:

Enable mode switching state (GROM-FM-GROM)

Once voice announcing the mode is heard press SCAN button

3There should be voice beep confirming full reset

You should be able to select and connect to GROM-CAR now

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.

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.

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

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