Symptoms
- Only one of the two SIM lines shows signal
- Calls or data default to the wrong SIM
- Second SIM shows as 'No Service' while the first works fine
- Data won't switch between the two SIMs as expected
Likely causes
- CommonData or call priority set to only one SIMDual-SIM phones require you to choose which line handles data and which handles calls by default.
- CommonSecond SIM or eSIM not properly activatedA newly added line needs full carrier-side activation before it will connect.
- PossibleBoth SIMs trying to use data simultaneously, which most phones don't supportMost dual-SIM phones can only use data on one line at a time, even if both can make calls.
- PossiblePhysical SIM not seated properly in a hybrid SIM trayTrays that share space between a second SIM and a memory card can have seating issues.
- Less commonCarrier compatibility issue between the two linesSome carrier combinations have technical limitations when used together on the same phone.
What to do
- Go to Settings > Cellular (or Network & Internet > SIMs) and check which SIM is set as the default for calls, texts, and data.
- Confirm both SIM lines are showing as active and not restricted in the dual-SIM settings menu.
- Check with each carrier that the specific line is fully activated on their system.
- If using a physical SIM in a hybrid tray, remove and reseat it carefully.
- Restart the phone after adjusting SIM priority settings.
- Manually select a network for the underperforming SIM in its individual network settings.
- Check for a carrier settings or software update.
- If one SIM consistently underperforms despite correct settings, contact that carrier to verify the line's status.
When to call a pro
If one SIM line consistently shows no service despite correct phone settings, contact that carrier to verify the line is properly provisioned.
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.