Troubleshooting
SIM Suddenly Not Working in Japan? How to Diagnose and Fix It
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If you only read this part
For foreigners, the overwhelming top cause is a failed payment suspending your line: the foreign card you registered expired, or the bank account ran dry. Second place goes to APN settings vanishing after an OS update or phone swap. Those two cover most cases.
Work through the steps below in order; they are sorted by likelihood.
Step 01
Did Your Payment Go Through?
Log into your carrier's member page or app and check your billing status. If you see an unpaid balance notice, you have found your answer. The three classic patterns:
- Your registered card expiredThe foreign card you signed up with, or your first Japanese card, quietly hit its expiry date. Update the card details.
- Insufficient bank balanceThe auto-debit bounced. You either wait for the retry date or pay via a convenience store payment slip.
- Card issuer blockFraud detection froze your card. This one needs a call to the card company.
After paying, reconnection takes minutes to a few hours. Restart the phone and give it time.
Step 02
Airplane Mode and Restart
Primitive, but it works. Airplane mode on, wait ten seconds, off again. Then a full restart. Physical SIM: eject and reseat it. eSIM: toggle the line off and on in settings. A surprising share of glitches are fixed by forcing a fresh connection to the tower.
Step 03
Check Your APN Settings
Signal bars but no data is the APN signature. Android phones can lose APN settings after OS updates or SIM swaps; iPhones misbehave when an old configuration profile is still installed. Carrier-by-carrier values and steps are in our APN settings guide.
Step 04
Check for Outages
Sometimes it is not you. Check your carrier's outage information page, or search "[carrier name] 障害" on X (Twitter) for real-time reports. If it is an outage, you wait; a few hours is typical.
Step 05
If Nothing Works
- povo's 180-day rulepovo 2.0 suspends lines that go 180 days without a paid topping purchase. povo users: check your contract status in the app.
- Prepaid or travel SIM expiryTourist SIMs die silently when their validity period ends. Check the expiry set at purchase.
- Physical SIM wearOld SIM cards stop being recognized as contacts wear out. Request a reissue from your member page; switching to eSIM is also an option.
- Carrier chat supportLead with your diagnostic results: payment confirmed, APN configured, no outage reported. It cuts the back-and-forth dramatically.
FAQ
Frequently asked questions
I paid, but I still have no service
Reconnection can take up to several hours to propagate. Wait an hour after paying, restart, and contact carrier support if it still fails.
What is the difference between "no signal" and "no data"?
No signal means the phone cannot see the network at all: a SIM, contract or coverage problem. Signal bars with no data flowing points to APN settings.
My Japanese SIM does not work while I am traveling abroad
Check that roaming is enabled in your settings and that your plan actually includes it. ahamo bundles roaming in its 30GB; most other plans sell it as a paid option.