Invalid MMI code

wojon

Hello,

Switched to a new phone with GOS recently. The phone works fine but when I want to check for my balance I usually just enter a MMI code within the dialer and then get the balance shown.
However, with GOS this doesn't seem to work. Whenever I enter the MMI code I get: Connection problem or invalid MMI code.

Is this a known limitation or a bug?

unwat

wojon

I don't recall anyone else reporting this kind of problem. Do you mind sharing with us the network you're using?

unwat

wojon

I did a little more digging to see what could cause this...

Firstly, disabling 2G is a feature added by Google to AOSP, so if we were to consider this a bug it would most likely be considered an upstream one. I checked Google's issue tracker, but I didn't see any reports of this issue for many years, most of which are labeled as "obsolete."

If it's not an upstream bug, I have another hypothesis...

GrapheneOS uses AOSP carrier settings, but changes them a little. The website explains it best:

The OS has a database of APN and other carrier configuration settings which determines how this works by default. Normally, carriers can force their configuration choices on users by making APNs read-only and disabling various configuration options. GrapheneOS ignores this and always allows configuring APNs, APN types, changing preferred network mode, toggling off 2G and using tethering regardless of what the carrier wants.

So, GrapheneOS allows you to disable 2G even if your carrier specifically forbids it in the carrier settings. The GrapheneOS script simply ignores that setting when parsing the carrier settings file.

(@treequell posted while I was writing this, thanks treequell!)

Considering MMI codes don't work for you with 2G disabled, but they do work for treequell, then I can only guess your carrier doesn't support disabling 2G yet. I'd suggest you either keep 2G enabled or temporarily enable it when checking your balance.

wojon

Hi. I am using the Telefonica network. @MetropleX @matchboxbananasynergy Do you have any idea about that issue?

unwat

wojon

I checked the AOSP carrier settings list, and Telefonica is on that list, so as far as I know it should work as it did on your previous phone.

I also looked around quickly to see if anyone else has had a similar problem. Someone reported they were getting the same error you're getting. One of the developers suggested the person reset mobile network settings here: Settings > System > Reset options > Reset Wi-Fi, mobile & Bluetooth.

They also suggested changing APN for the carrier here: Settings > Network & internet > SIMs > Access Point Names. Afterwards, restart and try again.

Lastly, you might need to contact your carrier if the problem persists. Maybe this is a common problem and they know of a way to fix it.

Here's a link to the dev messages I paraphrased.

Also, I personally have an issue with my carrier's app. I always have to disable my VPN for the app to work correctly. If you're using a VPN, maybe try disconnecting and trying again?

treequell

MMI codes work fine with my network (not Telefonica) on GrapheneOS.

unwat

wojon

Just to make sure, you're saying with 2G enabled, you're able to check your balance? If so, awesome. Wouldn't have expected that to be the culprit. Thanks for taking the time to find a solution.

I tried to check myself, but my carrier seems to have completely phased out MMI codes in favor of their app.

Maybe someone else can help...

treequell If you have the time and don't mind, do you get the same results as wojon? If you disable 2G in the SIM settings, do your network's MMI codes still work for you?

wojon

unwat Thank you very much for your comprehensive suggestions. I walked through your list of possible solutions and nailed the problem down further.

If I disable Settings > Network & internet > SIMs -> Allow 2G MMI codes don't work at all. If I enable that setting, MMI codes work. Is this expected behavior or is this a bug? Or maybe my SIM-card is too old? Either way, resetting mobile settings doesn't help. Also, the APN information is valid, I took it from the help page of my carrier.

treequell

unwat wojon

MMI codes work on my carrier, even with Allow 2G disabled (the default setting I believe).

Edit: So no, I don't get the same result as @wojon.

wojon

Thank you both for your extensive investigation and support. I assume that might be the case - my carrier simply doesn't support MMI codes that do not come over 2G. I will have to live with it and temporary enable it if I need it. This can be marked as solved I guess.