Seeing "No Service" or having zero bars on your new OnePlus 13 is incredibly frustrating. You just got a powerful phone, and now it can't make calls or use mobile data. This usually means the phone can't connect to your carrier's cellular network.
The good news is that most of the time, this is a temporary glitch you can fix yourself. I'd start with the simplest solutions first, as they often do the trick.
Restart Your OnePlus 13
This is always the first thing to try. A simple restart clears out temporary software bugs that can mess with the modem. Just press and hold the power button, then tap "Restart" on the screen.
If the screen is unresponsive, you'll need to force restart it. Press and hold the Volume Down button and the Power button together for about 10 seconds. Let go when you feel the device vibrate and see the OnePlus logo.
Check Airplane Mode and Mobile Data
It sounds obvious, but it's worth a quick look. Swipe down from the top of your screen twice to open the full Quick Settings panel. Make sure the Airplane Mode icon isn't highlighted.
While you're there, also tap the Mobile Data icon to turn it off and then back on. This refreshes the connection to the cellular network instantly.
Reinsert Your SIM Card
A loose or dirty SIM card is a very common culprit. Grab the SIM ejector tool that came in the box (a paperclip works in a pinch) and pop out the SIM tray.
Take out the SIM card, gently wipe the gold contacts with a soft, dry cloth, and then reseat it firmly in the tray. Push the tray back in until it clicks. Give your phone a minute to re-register on the network.
Toggle the SIM On and Off
OxygenOS lets you disable a SIM card digitally, which is another way to reset it. Go to Settings > Mobile Network.
Tap on your SIM card's name (like "SIM 1") and look for the switch at the top that says "Enable SIM." Turn it off, wait 10 seconds, and then turn it back on.
Reset Your Network Settings
If the basic steps don't work, your network configurations might be corrupted. Resetting them will clear all that out. Head to Settings > Additional Settings > Back Up and Reset > Reset Phone.
Here, tap on Reset Wi-Fi, mobile & Bluetooth. Confirm the reset. Remember, this will erase all saved Wi-Fi passwords and paired Bluetooth devices, so you'll have to reconnect to those later.
Manually Select Your Network Operator
Sometimes your phone gets stuck trying to connect to a weak or wrong tower. You can force it to search again. Go to Settings > Mobile Network.
Tap on your SIM card, then tap Network operators. Your phone will search for a moment. When the list pops up, select your carrier's name directly instead of leaving it on "Choose automatically."
Check and Update APN Settings
The Access Point Name (APN) is like the address your phone uses to find your carrier's data network. If these settings are wrong, you'll have no mobile data. Go to Settings > Mobile Network > tap your SIM > Access Point Names.
If the list is empty or looks wrong, tap the three-dot menu in the top right and select Reset to default. If that doesn't populate the correct settings, you'll need to get the exact APN details from your carrier's website or customer service and enter them manually here.
Update Your OxygenOS Software
Early software builds on new phones like the OnePlus 13 can have bugs that affect connectivity. OnePlus is usually quick to patch these. Make sure you're on the latest version.
Go to Settings > About device > tap on OxygenOS version. If an update is available, download and install it. It's a good idea to connect to Wi-Fi first, as these updates can be large.
Use the Phone Information Menu
Android has a hidden diagnostic menu that lets you tinker with the radio. Open your Phone app and dial *#*#4636#*#*. This should open the "Testing" menu.
Tap on Phone information. Look for a dropdown menu that says "Set preferred network type." Try selecting a different mode, like "LTE only," then switch it back to "NR/LTE/WCDMA/GSM" or whatever the global option is. You can also try tapping Turn off radio, then Turn on radio.
Test Your SIM Card in Another Phone
This step tells you if the problem is with your OnePlus 13 or with the SIM/carrier account. If you have an old phone handy, power it off and put your SIM card in it.
Turn that phone on. If it also shows no service, then the issue is with the SIM card or your carrier's service in your area. At that point, you should contact your carrier's support to check for outages or request a new SIM card.