Owners of Android smartphones (most often Samsung, but I think this is due to their greater prevalence) may encounter the error "Connection problem or invalid MMI code" (Connection problem or invalid MMI code in the English version and "Invalid MMI code" in older Android) when performing any action: checking the balance, the remaining Internet, the tariff of the telecom operator, i.e. usually when sending a USSD request.
In this manual, there are ways to fix the error. Invalid or incorrect MMI code, one of which, I think, is suitable for your case and will solve the problem. The error itself is not tied to certain phone models or operators: this kind of connection problem can occur when using Beeline, Megafon, MTS and other operators.
Note: you do not need all the methods described below if you just accidentally typed something on the phone keypad and pressed a call, after which such an error appeared. This happens. It is also possible that the USSD request that you used is not supported by the operator (check the official connection of the telecom operator if you are not sure if you enter it correctly).
The easiest way to fix the "Invalid MMI Code" error
If the error occurred for the first time, that is, you did not encounter it on the same phone earlier, most likely this is a random communication problem. The simplest option here is to do the following:
- Go to settings (at the top, in the notification area)
- Turn on airplane mode there. Wait five seconds.
- Turn off airplane mode.
After that, try again to perform the action that caused the error.
If after these steps the “invalid MMI code” error still persists, try turning the phone off completely (by holding the power button and confirming the shutdown), then turning it on again and then checking the result.
Correction in case of unstable working 3G or LTE (4G) network
In some cases, the cause of the problem may be a poor signal reception level, the main sign may be that the phone constantly changes the network - 3G, LTE, WCDMA, EDGE (i.e. you see different indicators above the signal level icon at different times).
In this case, try to select some specific type of network in the settings of the mobile network. The necessary parameters are in: Settings - "More" in the "Wireless Networks" - "Mobile Networks" - "Network Type".
If you have a phone with LTE, but the 4G coverage in the region is poor, install 3G (WCDMA). If bad with this option, try 2G.
SIM card issue
Another option, unfortunately, is also common and the most costly in time required to fix the error "invalid MMI code" - problems with the SIM card. If it is old enough, or has recently been removed, inserted, this may be your case.
What to do? Arming yourself with a passport and heading to the nearest office of your service provider: change your SIM card for free and quickly.
By the way, in this context, we can still assume a problem with contacts on the SIM card or on the smartphone itself, although it is unlikely. But just trying to remove the SIM card, wipe the contacts and re-insert it into the phone will not hurt either, since anyway you will most likely have to go to change it.
All of the following methods have not been personally verified, but simply encountered in discussions of errors of an invalid MMI code for Samsung phones. I don’t know how much they can work (and it’s hard to understand from the reviews), but I quote here:
- Try the query by adding a comma at the end, i.e. for example * 100 #, (a comma is put by holding the asterisk button).
- (From the comments, from Artem, according to reviews, many people work) In the "calls" - "location" settings, disable the "default camp code" parameter. In different versions, the android is located in different menu items. The parameter adds the country code “+7”, “+3”, for this reason requests stop working.
- On Xiaomi phones (maybe it will work for some others), try to go to settings - system applications - phone - location - disable country code.
- If you recently installed some applications, try uninstalling them, maybe they cause a problem. You can also check this by downloading the phone in safe mode (if everything works in it, then apparently the case is in applications, they write that FX Camera can cause a problem). You can see how to enter safe mode on Samsung on YouTube.
It seems to have outlined all the possible cases. I also note that when such an error occurs in roaming, not on your home network, it may be that the phone automatically connected to the wrong carrier or for some reason some of the requests are not supported at your location. Here, if possible, it makes sense to contact the support service of your telecom operator (you can do it on the Internet) and ask for instructions, perhaps choose the “right” network in the settings of the mobile network.