Xiaomi Keeps Losing Signal on O2 During Calls

Quick Answer:
If your Xiaomi drops calls or loses signal on O2, the most likely cause is VoLTE not working. First make a test call: if the 4G/5G icon disappears during the call, VoLTE is off. Enable it in Settings → SIM cards & mobile networks → O2 SIM → VoLTE → ON (dial *#*#86583#*#* first if missing). These are the most common fixes reported by Xiaomi users on O2.

Applies to Redmi, POCO and Xiaomi Phones

This guide applies to Xiaomi, Redmi and POCO devices running MIUI or HyperOS, including Redmi Note series, POCO X/F series, and Xiaomi 14/15.

Related O2 Call Problems – Also Covered Here

This guide also helps with: O2 signal drops during calls, O2 call failed on Xiaomi, O2 keeps disconnecting calls, and Xiaomi drops to 3G when calling on O2.

🔍 Step 1 – The Most Important Test (30 Seconds)

Make a test call and watch the network icon (4G/5G symbol):

  • If 4G/5G stays visible during the call → VoLTE is working. Your issue may be indoor coverage (see Fix D).
  • If it drops to 3G or H+ → VoLTE is NOT working. Go to Fix A below.

🔍 Step 2 – Diagnostic Gate (30 Seconds)

Before trying any fixes, answer these questions:

  1. Does signal drop during every call or only in specific locations (home/work)? If only at home/work, it may be a coverage issue – WiFi Calling often helps (Fix D).
  2. Does the problem start after a HyperOS update? Settings may have reset – go to Fix A below.

📊 Fixes by Probability (What Actually Works)

🔥 Critical Fixes (Most Common – Try First)

  1. Fix A – Make Sure VoLTE Is Working (includes phone setting + carrier provisioning – see detailed steps below)
  2. Turn off Battery saver – Settings → Battery → Battery saver → OFF. This can sometimes interfere with VoLTE.

📌 Optional Fixes (If Above Didn't Work)

  1. Check preferred network type – Settings → SIM cards & mobile networks → O2 SIM → Preferred network type → Select 5G/4G/3G auto (not "3G only").
  2. Disable 5G temporarily – Set preferred network type to 4G/3G/2G auto. In some areas, O2's 5G can be less stable for calls.
  3. Restart your phone – Clears temporary modem issues.

⚡ Rare Fixes (Last Resort)

  1. Reset network settings – Settings → Connection & sharing → Reset Wi-Fi, mobile networks, and Bluetooth.
  2. Replace SIM card – Very old O2 SIM cards may lack VoLTE profiles. Call 202 to request a replacement.

Fix A – Make Sure VoLTE Is Working (Phone + Carrier)

Without VoLTE, O2 calls drop from 4G/5G to 3G. 3G is weak or unavailable in many areas.

Step 1 – Enable VoLTE on your phone:

  • Settings → SIM cards & mobile networks → O2 SIM → VoLTE → Turn ON
  • If missing, dial *#*#86583#*#*, restart, then check again

Step 2 – Check O2 has enabled VoLTE on your account:

  • Call O2: 202 (free) or 0344 809 0202
  • Ask: "Is VoLTE enabled on my account? Please check and enable it"
  • Request: "Please send a new SIM profile to my phone"
  • Restart your phone after the call

Step 3 – Test again: Make a call. If 4G/5G stays visible, VoLTE is working.

Fix B – Turn Off Battery Saver

On some Xiaomi devices, Battery saver can interfere with VoLTE background processes.

Settings → Battery → Battery saver → OFF

Fix C – Enable WiFi Calling (Best for Indoor Coverage)

If you lose signal indoors at home or work, WiFi Calling completely bypasses O2's mobile signal issues. Older buildings, thick walls, and basement flats can weaken O2 indoor coverage – WiFi Calling fixes this.

Enable WiFi Calling: Settings → SIM cards & mobile networks → O2 SIM → WiFi Calling → ON. On some Xiaomi devices, dialing *#*#869434#*#* may restore the option if missing – restart after dialling.

Note: You must be connected to WiFi. Calls will route over your broadband.

Fix D – Disable 5G Temporarily (For Unstable Areas)

In some areas, O2's 5G can be less stable for calls. Forcing 4G keeps your phone on the more reliable 4G network.

Navigation: Settings → SIM cards & mobile networks → O2 SIM → Preferred network type → Select 4G/3G/2G auto

Test Your SIM in Another Phone

  • If the other phone also drops calls on O2: Problem is your O2 account or SIM. Call 202.
  • If the other phone works normally: Problem is your Xiaomi. Reset network settings (Fix 6).

Quick Questions

Why does my Xiaomi lose signal on O2 during calls?
Most commonly VoLTE is not working. Make a test call – if 4G/5G drops to 3G, VoLTE is off. Enable it in settings (dial *#*#86583#*#* first if missing).

Does O2 support VoLTE on Xiaomi?
Yes, O2 supports VoLTE on most recent UK Xiaomi models. You may need to call 202 to enable it on your account.

Why does O2 signal drop indoors on Xiaomi?
Older buildings, thick walls, and basement flats can weaken O2 indoor coverage. Enable WiFi Calling as a workaround – it uses your broadband instead of mobile signal.

Will resetting network settings delete my photos?
No. Only saved Wi-Fi passwords and Bluetooth devices are removed.

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