Check these first
Do not assume the cause from the symptom alone. First determine whether the issue affects the whole phone, one app, one connection, or one accessory. Work from low-impact checks toward recovery or repair.
- Record the exact message: No SIM, Invalid SIM, No service, or Emergency calls only
- Note whether the SIM worked before or the problem began after changing phones
- Check whether the phone is locked to a different carrier
Critical diagnosis for this symptom
Separate physical SIM detection from carrier provisioning with controlled comparisons.
Check power-off and tray handling requirements before removing a SIM.
Escalate with device, OS, error, and reproduction details when the issue persists after restart, controlled comparison, and update checks, or when physical damage, abnormal heat, account suspension, or carrier provisioning is suspected.
Narrow down the cause
| Scope of the issue | Where to check next |
|---|---|
| Only one app is affected | Check app permissions, updates, storage, cache, and reinstall options |
| The whole phone is affected | Check restart, system updates, free storage, and system settings |
| Other devices have the same issue | Check the network, service, charger, or accessory |
| The issue began after a drop or liquid exposure | Avoid repeated power or charging attempts and contact official support |
See the troubleshooting flow
Safe step-by-step process
Complete one step at a time and test after each change. Do not change several settings at once.
- 1Toggle Airplane mode and restart the phone.
- 2Open SIM settings and confirm the physical SIM or intended dual-SIM line is enabled.
- 3Power off, open the tray according to the manual, and reseat the SIM with the notched corner aligned.
- 4Inspect the SIM and tray for bending, cracks, debris, or moisture. Do not scrape the contacts.
- 5When possible, have the carrier or another compatible phone test the SIM to separate SIM and device faults.
- 6Ask the carrier about replacement, supported bands, carrier lock, activation, and account status.
Actions to avoid
- Forcing the tray open while the phone is powered on
- Cutting or adapting a SIM to a different size
- Guessing a SIM PIN or PUK repeatedly
Prevent the issue from returning
- Store the SIM tool and account information safely
- Confirm SIM format and network compatibility before changing phones
Frequently asked questions
What if my screen looks different?
Menu names and locations vary by OS, manufacturer, model, region, and software version. Use the Settings search field and check the manufacturer guide for your exact model.
When should I stop troubleshooting?
Stop as soon as the issue is fixed. Change one setting at a time so you can identify what solved the problem and reverse it if necessary.
What should I do if the issue remains?
Record how to reproduce it, verify your backup, and contact the manufacturer, carrier, or app provider most closely related to the problem.