Seeing "No Service" or a missing signal bar on your OnePlus 12 can stop you from making calls, sending texts, or using mobile data. It's a common hiccup that usually has a simple fix, especially on newer phones running OxygenOS.
The first thing I'd try is the classic restart. Press and hold the Power button for 10-15 seconds until the screen goes black and the OnePlus logo reappears. This force restart clears out any temporary software glitches that might be blocking the cellular radio, and it solves the issue more often than you'd think.
Check Your Basic Connection Settings
It sounds obvious, but double-check that Airplane Mode isn't accidentally enabled. Swipe down from the top of your screen twice to open the full Quick Settings panel and make sure the airplane icon isn't highlighted. While you're there, tap the mobile data icon to turn it off, wait a few seconds, and then turn it back on.
Next, take a quick look at your SIM card. Power off your OnePlus 12, pop out the SIM tray with the included tool, and carefully remove the SIM. Give the gold contacts a gentle wipe with a soft, dry cloth and reseat it firmly in the tray. A loose or dusty SIM is a surprisingly frequent culprit for signal problems.
Reset Your Network Settings
If the basics don't work, a network settings reset is a strong next step. This clears all your saved Wi-Fi networks, Bluetooth pairings, and cellular configurations without touching your personal photos, messages, or apps.
Go to Settings > Additional settings > Backup and reset > Reset phone > Reset Wi-Fi, mobile & Bluetooth. Confirm the reset and let your phone reboot. After it restarts, you'll need to reconnect to Wi-Fi and re-pair Bluetooth devices, but it often resolves persistent cellular connection bugs.
Manually Select Your Network Operator
Sometimes your phone gets stuck trying to connect to a weak or unavailable network tower. You can force it to search for and lock onto your proper carrier. Head to Settings > Mobile network > SIM 1 (or 2) > Network operators.
Tap "Search networks" and wait for the list to populate. Instead of leaving it on "Automatic," select your carrier's name directly from the list. This tells your OnePlus 12 to stop searching and connect specifically to your provider's network.
Verify and Update Your APN
Your Access Point Name (APN) is the gateway your phone uses to connect to your carrier's mobile data network. If these settings are wrong or corrupted, you'll lose data and sometimes voice service. To check them, go to Settings > Mobile network > SIM 1 > Access Point Names.
You should see a list, often with your carrier's name. If the list is empty or you're unsure, the best move is to contact your carrier's support. They can give you the exact APN settings to enter or often send a configuration message that sets it up automatically.
Use the Phone Information Menu
Android has a hidden diagnostic menu that's very useful for radio issues. Open your Phone dialer and type *#*#4636#*#*. This should open the "Testing" menu. Tap "Phone information."
Here, you can see the status of your radio. First, tap "Run Ping Test" to check for a basic data connection. If that fails, look for the "Set preferred network type" dropdown. Try changing it to another option (like "NR/LTE/GSM/WCDMA") and then back to your original setting. You can also tap "Turn off radio" and then "Turn on radio" to refresh the connection.
Review Your SIM & Account Status
It's worth checking if the problem is with your account or physical SIM. A quick call to your carrier's customer service can confirm if there's an outage in your area or if your account has been suspended for non-payment. They can also perform a network refresh on their end for your line.
If you have access to another unlocked phone, try putting your SIM card in it. If the other phone also shows no service, the issue is almost certainly with the SIM or your carrier account. If the other phone gets a signal perfectly, then the problem is localized to your OnePlus 12.
Check for Software Updates
OnePlus regularly releases OxygenOS updates that include stability improvements and bug fixes for connectivity. An outdated system can sometimes cause radio problems. Go to Settings > About device > OxygenOS version and tap the icon at the top to check for updates.
If an update is available, download and install it. Make sure your phone is connected to Wi-Fi and has at least a 50% charge, or better yet, plug it into the 100W SUPERVOOC charger. After the update completes, your phone will restart, which applies the fixes and gives the cellular modem a fresh start.
Disable VPN or Custom DNS Services
If you use a VPN app or have configured a custom DNS (like through a private browsing app), these can interfere with how your phone routes its network traffic. Open your VPN app and disconnect from it, or go to Settings > Wi-Fi & network > Private DNS and set it to "Off."
After disabling these services, restart your phone and check if your signal returns. You can always re-enable them later once you've confirmed they were the cause of the conflict.
Consider a Factory Reset
This is a last resort, but if you've tried every other fix and your OnePlus 12 still won't connect to any network, a factory reset can wipe out any deep-seated software corruption. Before you do this, it's absolutely critical to back up everything you want to keep.
Go to Settings > Additional settings > Backup and reset > Reset phone > Erase all data (factory reset). Follow the prompts to confirm. After the reset is complete, set up your phone as new initially, without restoring a backup, and see if the signal returns. This helps determine if the problem was with your system data.