If your OnePlus Nord 4 shows a "Not registered on network" error or you can't make calls or send texts, it means your phone can't connect to your carrier's cellular service. This is a frustrating issue that leaves you without basic phone functions. The problem can be caused by anything from a simple software glitch to a more serious hardware concern.
Before you start worrying, the first thing to check is your IMEI number. Open your phone dialer and type *#06#. You should see a 15-digit number. If it shows "null," "unknown," or a string of zeros, that's a specific problem we'll address. More often than not, a few quick software fixes can get you back online.
Start With a Force Restart
This is my go-to first step for any weird phone behavior. A force restart clears the phone's temporary memory and can resolve minor software conflicts that block network registration. On the OnePlus Nord 4, press and hold the Power button for about 10 seconds until you feel it vibrate and the screen goes black. Release the button and let the phone boot up completely before checking for service.
Toggle Airplane Mode
This trick forces your phone to completely disconnect from and then reconnect to all wireless networks. Swipe down from the top of your screen to open the Quick Settings panel. Tap the Airplane Mode icon to turn it on, wait for about 15 seconds, then tap it again to turn it off. You should see the signal bars disappear and then hopefully reappear as it searches for your network again.
Check and Reseat Your SIM Card
A loose or dirty SIM card is a surprisingly common culprit. The Nord 4 uses a dual nano-SIM tray. Grab the SIM ejector tool that came in the box and gently push it into the small hole on the left side of the phone. Pull the tray out and carefully remove the SIM card.
Inspect the gold contacts on the SIM for any dirt or damage. Give both the SIM and the slot a gentle blow to dislodge any dust. Reinsert the SIM, making sure it's seated correctly in the tray, and push the tray firmly back into the phone. Power the device on and see if it connects.
Verify Your Carrier Account Status
Sometimes the issue isn't with your phone at all. If your prepaid plan has expired, your postpaid bill is overdue, or there's an account issue, your carrier will block service. Try logging into your carrier's website or app from another device, or give them a call from a different phone to confirm your line is active and in good standing.
Reset Your Network Settings
This is a more thorough step that wipes all your saved network configurations. It will delete your Wi-Fi passwords, Bluetooth pairings, and cellular network settings, forcing your phone to start fresh. To do this on your Nord 4, go to Settings > Additional settings > Backup & reset > Reset phone > Reset network settings.
Tap to confirm. Your phone will restart. After it boots, you'll need to reconnect to Wi-Fi and re-pair Bluetooth devices, but it often clears out corrupted settings that were preventing network registration.
Manually Select Your Network
Your phone might be struggling to automatically connect to the right network band. You can try forcing it to use a different one. Navigate to Settings > Mobile network > SIM & network > Preferred network type.
If you have it set to "5G," try switching it to "4G/3G/2G." If it connects on 4G, the issue might be related to 5G coverage or configuration in your area. You can also try going to Network operators in the same menu and tapping "Search networks," then manually selecting your carrier from the list.
Update OxygenOS
OnePlus regularly releases software updates that fix bugs, including those related to network connectivity. An outdated version of OxygenOS could be the root of your problem. Connect to Wi-Fi and go to Settings > About device > OxygenOS version.
Tap on the icon at the top right (it looks like three dots or a download arrow) to check for updates. If an update is available, download and install it. The 100W SuperVOOC charging means this won't take long, but make sure your battery is above 30% before starting.
Clear the Phone Services Cache
The system app responsible for managing calls can sometimes get bogged down with corrupted temporary data. Clearing its cache is a safe way to refresh it without losing any personal information. Go to Settings > Apps > App management.
Tap the three-dot menu in the top right and select "Show system." Scroll down and find "Phone Services." Tap on it, then go to Storage usage > Clear cache. Restart your phone afterward to let the app rebuild its cache cleanly.
Test With a Different SIM Card
This step helps you pinpoint whether the problem is with your SIM card or the phone itself. If you can, borrow a known-working SIM card from a friend or family member (on any network) and insert it into your Nord 4. If their SIM card connects to a network without issue, then your original SIM is likely faulty or deactivated.
You'll need to contact your carrier for a replacement. If the borrowed SIM also fails to register, the issue is almost certainly with your phone's hardware or a deeper software problem.
Perform a Factory Reset
This is the last resort software fix. A factory reset will erase all data, apps, and settings from your phone, returning it to its original out-of-the-box state. It will eliminate any problematic app or deeply corrupted system file. Before you begin, ensure you have a complete backup of your photos, contacts, and important files.
Go to Settings > Additional settings > Backup & reset > Erase all data (factory reset). Follow the prompts to confirm. After the reset is complete, set up the phone as new without restoring a backup initially, just to test the network connection. If the "not registered" error is still there after a clean factory reset, the issue is likely a hardware fault with the phone's internal antenna or modem, and professional repair would be needed.
