Seeing a "No SIM" or "SIM card not detected" message on your OnePlus 12 can stop you from making calls or using mobile data right when you need it. This is usually a temporary glitch you can fix yourself with a few simple steps.
Restart Your OnePlus 12
This is the most effective first step. A quick restart clears out temporary software bugs that can confuse the SIM manager. Just press and hold the power button until the power menu appears, then tap "Restart."
If the screen is frozen and you can't access the menu, you can force a restart. Press and hold the power button for about 10 to 15 seconds until you feel the phone vibrate and see the OnePlus logo appear on the screen.
Toggle Airplane Mode On and Off
Swipe down from the top of your screen twice to open the full Quick Settings panel. Tap the Airplane mode icon to turn it on, wait about 10 seconds, then tap it again to turn it off.
This forces your phone's modem to completely reset its connection to the network. It's a quick refresh that often solves detection issues without needing to restart.
Check Your SIM Card Status in Settings
Sometimes, a SIM can get disabled in the software. Open your Settings app and go to Mobile network. Tap on the SIM slot you're using (SIM 1 or SIM 2).
Make sure the switch at the top for that SIM card is toggled on. While you're here, also check that "Mobile data" is enabled for that line if you're trying to use the internet.
Inspect and Clean the Physical SIM Card
Turn your OnePlus 12 off completely. Use the SIM ejector tool that came in the box (or a small paperclip) to gently push into the tiny hole on the SIM tray on the bottom edge of the phone.
Carefully pull the tray out and remove the SIM card. Look at the gold contacts on the card for any dirt, dust, or scratches. Gently wipe them with a clean, dry microfiber cloth.
Also, peek into the SIM slot itself for any debris. Blow into it gently or use a can of compressed air to clear out any dust. Reinsert the SIM, making sure it's seated correctly in the tray, and push the tray back in until it clicks.
Test the SIM Card in Another Phone
This is the best way to figure out if the problem is with your SIM or your OnePlus 12. Take your SIM card and put it into another unlocked phone.
If the other phone also says "No SIM," then the issue is definitely with the SIM card itself. You'll need to contact your carrier's support to get a replacement SIM sent to you.
If the SIM works perfectly in the other phone, then the issue is localized to your OnePlus 12, and we can continue with the software fixes below.
Update Your Phone's Software
Outdated system software can have bugs that affect the modem or SIM management. OnePlus regularly releases updates with fixes for these kinds of issues.
Go to Settings > About device > OxygenOS version and tap on 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 a good battery charge first.
Reset Your Network Settings
This will clear all your saved Wi-Fi networks, Bluetooth pairings, and cellular network configurations back to default. It won't delete your personal files like photos or messages.
To do this, navigate to Settings > Additional settings > Backup & reset > Reset phone > Reset network settings. Confirm the reset and let your phone reboot.
After the restart, you'll need to reconnect to Wi-Fi and re-pair Bluetooth devices, but it often resolves persistent SIM and network glitches.
Manually Select Your Network Operator
Your phone usually picks the best network automatically, but sometimes this process can get stuck. You can force it to search and connect.
Go to Settings > Mobile network. Tap on your SIM, then look for "Network operators" or "Choose network." Tap "Search now" and wait for the list to populate.
Select your carrier's name from the list. If it connects successfully, your SIM should be recognized. If it fails, there might be a temporary outage in your area.
Configure the Correct APN Settings
APN settings tell your phone how to connect to your carrier's mobile data network. If these are wrong, you might see a "No SIM" error or have no internet.
In Settings > Mobile network, tap on your SIM, then tap "Access Point Names." If there are existing APNs, tap the three-dot menu and select "Reset to default."
If that doesn't work, you may need to enter them manually. Your carrier's exact APN settings are usually listed on their official support website. You'll need to create a new APN and input details like the name, APN, MMSC, and MCC/MNC.
Consider an eSIM as an Alternative
The OnePlus 12 supports eSIM technology. If your physical SIM card slot seems faulty or you keep having issues, switching to an eSIM is a great workaround.
Contact your carrier's customer support and ask if they support eSIM activation for the OnePlus 12. They can guide you through converting your physical plan to a digital one, which you then download directly to your phone through a QR code or an app.