- MMI (Man-Machine-Interface) codes are special characters such as Star (*) or Pound (#)
- Fixes include toggling Airplane Mode, restarting the phone, and adding a comma to the code
- Phones with dual SIM cards or an eSIM can often fix the issue by turning off one SIM
- Older fixes that switch the phone to a 2G/3G network no longer work in the US since 3G has been shut down
If you have an Android smartphone with an error “Connection Problem or Invalid MMI Code”, there are several fixes that can solve the problem.
The error can happen on any Android smartphone, such as Samsung, Google Pixel, Motorola, or OnePlus.
An iPhone can have the same type of problem, but it will show a different error message.
While the location of settings and options are different, the issues and fixes below are the most common causes of the error.
What is an MMI Code?
An MMI code is the special characters such as Star (*) or Pound (#), which are used for commands on a cell phone network.
MMI is short for Man-Machine-Interface and are available for a variety of functions and options.
Common examples are checking a prepaid balance, setting up call forwarding, or entering a carrier code such as *#06# to see the phone’s IMEI number.
What is a Connection Problem or Invalid MMI Code?
An invalid MMI code is a mobile network error that has a range of problems, from connection issues to authorization issues.
It mainly is a problem with a SIM Card and is an error that happens commonly with Dual SIM Card smartphones.
There are several fixes that can solve the issue from refreshing the network connection, to changing which SIM the phone uses for calls.
The most common problem with a MMI Code Error is the smartphone SIM Card having a problem with authorization on the mobile network.
The error is the same with both physical SIM cards and eSIM.
Most new smartphones now use an eSIM, and many are sold in the US as eSIM only, but it is still an authorization code the same as a physical SIM card.
Keep in mind, some carriers have also dropped support for older MMI codes, so if a code has never worked on your carrier, it may simply no longer be supported.
7 Fixes for Connection Problem or Invalid MMI Code
- Toggle Airplane Mode On and Off
- Restart the Smartphone
- Add a Comma or Plus Sign to the Code
- Turn Off One SIM Card
- Clear the Phone App Cache
- Change the Mobile Network Mode
- Go to Settings
- Click Connections
- Click Mobile Networks
- Click Network Mode
- Select the Auto option such as 5G/LTE/3G/2G (auto connect). (If it is already on Auto, try switching it to LTE only and back.)
- Go To Settings
- Select Network & internet
- Select SIMs and tap the SIM Card
- Select Preferred Network Type
- Select 5G (recommended) or LTE
- Reset Network Settings
The quickest fix is to turn Airplane Mode on, wait 15-20 seconds, and turn it back off.
This forces the phone to disconnect and re-register with the mobile network, which will often clear the error.
Swipe down from the top of the screen to open the Quick Settings and tap the Airplane Mode icon.
Once the signal bars come back, try the MMI code again.
If Airplane Mode doesn’t work, restarting the smartphone can often get it working again.
The phone may have an error which a restart will often clear when reset.
Be sure to choose Restart and not just Power Off, and wait for the phone to fully boot back up before trying the code again.
This is a simple trick that fixes the error for many people.
Type the code as normal and then add a comma at the end, so *123# becomes *123#,
The comma adds a short pause that gives the phone time to process the code.
If the comma doesn’t work, try adding a plus sign after the first star, so *123# becomes *+123#
To get the plus sign, press and hold the 0 key on the dialer.
If you have a Dual SIM card smartphone turning off the unused SIM Card can often solve the problem.
This also applies if the phone has a physical SIM card and an eSIM that are both active.
On a Samsung phone go to Settings–> Connections–> SIM manager (older phones call it SIM card manager).
On a Google Pixel go to Settings–> Network & internet–> SIMs.
Turn off the unused SIM Card and test to see if the error clears.
If you are unsure which SIM Card is unused simply test each one, on and off, to see if it works.
If you want to keep both SIM cards on, another option is in the same SIM manager menu under Calls to set it to Ask every time.
The phone will then ask which SIM to use when the code is dialed, and you can pick the one with the active plan.
The next option is to clear the cache for the Phone app. This data may have bad information that is causing an error.
Go to Settings–> Apps–> Phone–> Storage.
Choose the option to Clear Cache.
Clearing the cache is safe and will not delete any call history or contacts.
After clearing the cache check to see if the phone works, if not try the next method.
Setting the mobile network mode to Auto is a common fix.
Older guides say to switch the phone to a 2G or 3G network such as GSM/WCDMA, but this no longer works in the US since AT&T, T-Mobile, and Verizon all shut down their 3G networks in 2022.
The best option now is to set the network mode to the Auto setting that includes 5G, LTE, and everything else, so the phone can pick the best network for the location.
The location to change the network can vary from phone to phone.
How To Change the Mobile Network Mode Samsung Smartphone
How To Change the Mobile Network Mode Google Pixel Smartphone
While in the Mobile Networks menu, some Samsung users have also had luck turning off VoLTE calls, dialing the code, and then turning VoLTE back on.
If none of the above works, resetting the network settings will clear out any bad mobile network, WiFi, and Bluetooth settings.
Keep in mind this will remove saved WiFi passwords and paired Bluetooth devices, so they will need to be set up again.
On a Samsung phone go to Settings–> General management–> Reset–> Reset network settings.
On a Google Pixel go to Settings–> System–> Reset options–> Reset Wi-Fi, mobile & Bluetooth.
The phone will restart and should have a fresh connection to the mobile network.
Summary
If you get the error “Connection Problem or Invalid MMI Code” on your smartphone it can no doubt be very annoying.
The first step is to toggle Airplane Mode on and off, or restart the smartphone to see if the error clears.
Next, try adding a comma or plus sign to the code, which is a quick fix that works for many.
If you are using a dual SIM card smartphone disabling the one not currently being used can also get the phone working properly again in some cases.
Clearing the Phone app cache or changing the network mode to Auto can also be a solution.
And lastly, resetting the network settings will give the phone a fresh start on the mobile network.
If the code still does not work after all the fixes, contact the carrier since the code may no longer be supported.
Have you had a smartphone that gives a” Connection Problem or Invalid MMI Code” Error? Let us know your fix and thoughts below.
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