Why Is My Mobile Data Not Working?

Mobile data does not fail in one way. It fails in about five, and what the phone is showing you narrows it down before you change a single setting. "No Service" and "full bars but nothing loads" are different problems with different causes, and treating them the same is how people end up resetting a phone that was one toggle away from working.

This page is the diagnosis. If you would rather just work through the repairs in order, the fix sequence does that instead.

Match the symptom, and you have usually halved the search:

• No Service, or no bars at all — the line is not registered on any network. This is a registration problem, not a data problem.
• Full bars, nothing loads — the line is registered and the network is refusing the data session. Almost always a setting.
• Works on wifi, not on cellular — mobile data is off for that line, or the other line is carrying it.
• Some apps work, others do not — a per-app restriction, low data mode, or a VPN, not the connection.
• Connected but very slow — usually an allowance spent and the plan throttled rather than anything broken.

Nothing you change on the phone will help with these — the account or the hardware is the constraint.

• The phone is carrier-locked. It accepts the profile and then never registers, which reads as a broken plan — Apple’s invalid SIM and no SIM checklist opens with exactly this, and with where the phone reports it. Ten seconds to check.
• The plan expired, or the allowance is spent. Providers usually cut data rather than warning first.
• The profile was never activated — bought and installed but never connected, on a plan that needed a manual start.
• The account is suspended, most often over an unpaid bill or a payment flagged after purchase.

These are the common ones, and all are reversible in under a minute:

• Data roaming is off for the travel line. A travel eSIM always needs it on — on for one line, off for the other. The toggle lives under Cellular Data Options, which Apple’s guide to the cellular data settings walks through.
• The wrong line is set to carry cellular data. Two lines, one data setting, and the phone will not guess.
• Low data mode or a data saver is throttling background traffic, which looks like some apps working and others not.
• A VPN is connected but its server is unreachable, so traffic goes nowhere while the phone reports a fine connection.
• The APN is wrong or missing. Genuinely rare, and worth ruling the others out first.

On Android the same settings carry different names, and Google’s Pixel guide to fixing mobile connectivity maps them screen by screen. But sometimes nothing is wrong with the phone or the plan at all:

• No coverage. Rural areas, basements, tunnels and thick stone all do it, and a travel plan roams onto one specific local network that may not be the strongest one there.
• Automatic network selection settling on an operator your plan has no agreement with. Selecting manually fixes this and is worth trying early.
• Congestion — a stadium, a festival, an airport at peak. The line works and nothing moves.
• Band mismatch, on an imported phone missing the local frequencies. Uncommon, but it produces a stubborn partial signal.

A plan that has never connected once is usually roaming, the data-line setting, or a carrier lock — in that order. A plan that worked and stopped is usually the allowance. Neither is a reason to buy a second plan before checking. Compare on price per GB by destination when you do buy.