Xiaomi VoLTE Not Working on O2 Germany

Xiaomi VoLTE Not Working on O2 Germany (2026 Fix)

If your Xiaomi, Redmi or POCO phone drops to 2G/3G during calls, shows "Can't use VoLTE", or the VoLTE option is missing or greyed out on O2 Germany, this guide covers common troubleshooting steps. This issue can affect both 4G and 5G connections.

Diagnose the Issue First

Before making changes, determine the pattern of your VoLTE issue:

• Is the option missing entirely? – The VoLTE toggle does not appear in your SIM settings.
• Is the option visible but calls drop to 2G/3G? – The toggle is on, but during calls the network indicator changes from 4G/5G to 2G/3G.
• Does it work on one SIM but not the other? – In dual-SIM setups, VoLTE availability may depend on which SIM is selected for mobile data.
• Does it work on some networks but not others? – VoLTE availability can vary by roaming partner.
• Test your SIM in another VoLTE-capable phone – This is the quickest way to identify if the issue is your Xiaomi device or your SIM/plan.

Why This Happens

• Plan or carrier restrictions – Some O2 MVNOs may have inconsistent VoLTE support.
• Dual-SIM configuration – On some Xiaomi dual-SIM devices, VoLTE availability may depend on which SIM is selected for mobile data.
• Carrier provisioning – VoLTE may need to be activated on O2's side. In some cases, toggling the VoLTE setting off and on while on LTE can trigger registration.
• IMS registration failure – The phone's IMS (IP Multimedia Subsystem) may not be properly registered on the network.
• Software or configuration issues – Xiaomi's VoLTE carrier check may block the feature, even when the network supports it.

Check Plan & Carrier Support

Before troubleshooting your device, verify that your O2 plan supports VoLTE:

• O2 Postpaid (contract) plans – Generally support VoLTE.
• O2 Prepaid plans – VoLTE availability depends on the specific O2 prepaid service and current carrier provisioning.
• O2 MVNOs – Support varies. If you are on an MVNO, contact your provider directly to confirm whether your specific tariff includes VoLTE.

Test SIM in Another Phone

Why this matters: This is the quickest way to determine if the issue is your Xiaomi device or your SIM/plan.

• Insert your O2 SIM into another phone that supports VoLTE
• Check if VoLTE works on the other phone (look for LTE/4G indicator during a call)
• If VoLTE works normally on the other phone, the issue is more likely related to your Xiaomi device or its configuration – continue with the steps below
• If VoLTE also doesn't work on the other phone, the problem is more likely related to your SIM or plan – contact O2

If the SIM works normally in another phone, continue with Step 1.

Step 1: Enable VoLTE in Settings

Why this matters: VoLTE must be explicitly enabled on your Xiaomi device.

• Settings → SIM cards & mobile networks
• Tap your O2 SIM
• Look for VoLTE, 4G calling, or Use VoLTE and toggle it ON

Important notes:

• On some Xiaomi models, the VoLTE option may be hidden by default and needs to be unlocked via a diagnostic code.
• On some Xiaomi dual-SIM devices, VoLTE availability may depend on which SIM is selected for mobile data.

If the option is enabled but VoLTE still doesn't work, move to Step 2.

Step 2: Check VoLTE with the Hidden Xiaomi Code

Why this matters: Xiaomi devices have a hidden diagnostic code that can toggle the VoLTE carrier check. In some cases, this check blocks VoLTE even when the network supports it.

1. Open the Phone app
2. Dial *#*#86583#*#*
3. If supported, the phone may display a message indicating that the VoLTE carrier check has been disabled.
4. This may enable the VoLTE option if it was previously hidden.
5. Restart your phone and check if VoLTE works

Note: This code toggles the carrier check on and off. Dialing it again will re-enable the check.

If VoLTE still doesn't work, move to Step 3.

Step 3: Check IMS Registration Status

Why this matters: VoLTE requires IMS (IP Multimedia Subsystem) registration. The IMS status can reveal whether the phone is successfully registered for VoLTE on O2's network.

1. Open the Phone app
2. Dial *#*#4636#*#*
3. Select Phone information
4. Tap the three dots in the top right corner
5. Select IMS Service Status
6. Check if Voice over LTE shows as Available or Registered

Note: The IMS Service Status menu is not available on every Xiaomi model or HyperOS/MIUI version. If the menu is not available, proceed to Step 4.

If IMS shows "Not available" or "Not registered":

• Try toggling Airplane Mode on and off to re-register
• Try toggling VoLTE off and on in Settings while on LTE

If IMS registration fails, move to Step 4.

Step 4: Reset Network Settings

Why this matters: This resets Wi-Fi, mobile data, and Bluetooth settings without deleting personal data. It clears corrupted network configurations that may be preventing IMS registration.

1. Settings → Connection & sharing (HyperOS) or Settings → Additional settings → Backup & reset (MIUI)
2. Select Reset Wi-Fi, mobile & Bluetooth or Reset network settings
3. Confirm the reset
4. Restart your phone
5. Wait a few minutes for the phone to reconnect to the network
6. Re-enable VoLTE in Settings
7. Check if VoLTE works (look for LTE/4G indicator during a call)

If VoLTE still doesn't work, move to Step 5.

Step 5: Check for System Updates

Why this matters: Software updates often include modem firmware and IMS improvements that can enable or improve VoLTE.

1. Settings → About phone → Check for updates
2. Install any available updates
3. Restart your phone and check if VoLTE works

If you're already on the latest version and VoLTE still doesn't work, contact O2 or Xiaomi support.

Contact Carrier (When Required)

Contact O2 Germany if:

• Your SIM has no VoLTE in other phones as well (plan or provisioning issue)
• You've tried all steps above and VoLTE still doesn't work
• You need to verify that your plan includes VoLTE
• You need to check that your SIM and account are properly provisioned for VoLTE

Contact Xiaomi EU Support if:

• You've tried all steps above and VoLTE still doesn't work
• You've tested your SIM in another phone and it works normally
• You suspect a software or hardware issue with your device

Final Verdict

If your Xiaomi won't use VoLTE on O2 Germany, start by testing your SIM in another phone – this is the quickest way to determine if the issue is your device, your SIM, or your plan. If the SIM works normally elsewhere, enable VoLTE in Settings and note that on some Xiaomi dual-SIM devices, VoLTE availability may depend on which SIM is selected for mobile data. If the VoLTE option is hidden, use the Xiaomi diagnostic code *#*#86583#*#* to disable the carrier check, which may reveal the VoLTE option. You can also check IMS registration status using *#*#4636#*#* to confirm whether the phone is properly registered for VoLTE on O2's network. If all else fails, reset network settings or check for system updates. Contact O2 to verify your account provisioning if none of these steps resolve the problem.

Frequently Asked Questions