---
title: SIM cards troubleshooting
description: >-
  Diagnose SIM card issues like searching or unregistered status, USSD errors,
  missed SMS, or unreachable robots with this troubleshooting guide.
lastUpdated: "2026-09-23"
---

> **For AI agents:** the complete documentation index is at [llms.txt](/llms.txt). Append `.md` to any page URL for its markdown version.

A SIM that misbehaves shows up either through its status (searching, unregistered) or through recurring errors in test results. Here is the diagnosis for each case.

<AccordionGroup>
<Accordion title="The SIM status stays on searching">
1. Reboot the slot, or the robot.
2. If the status stays **searching** after 10 minutes, insert the SIM in a phone and check whether it connects to the network.
3. If it connects in a phone, the modem's IMEI has likely been banned by the operator: investigate that side.
4. If it does not connect in a phone either, the SIM itself has a problem or the network coverage is very poor.
</Accordion>
<Accordion title="The SIM status stays on unregistered">
The SIM has probably been deactivated by the operator because it always stayed connected to the same antenna. Reboot the modem; if it stays unregistered, test the SIM in a phone and replace it if it does not connect.
</Accordion>
<Accordion title="A USSD test fails with Network Timeout (+CUSD 5)">
The cellular network did not answer a USSD session opening request. Possible causes: bad network coverage, an outdated USSD licence, or an overloaded USSD server.

To confirm the request left the modem, open the pcap artifacts (radioframes) attached to the test result and look for:

- `UplinkDirectTransfer ... invoke processUnstructuredSS-Request`: the request was sent.
- `DownlinkDirectTransfer ... invoke unstructuredSS-Request`: the network replied.

If the request is sent but never answered, contact your USSD provider.
</Accordion>
<Accordion title="A USSD test fails with CME 100">
Reboot the modem, then contact support if it persists.
</Accordion>
<Accordion title="A USSD test fails with Connection problem or invalid MMI code (CME 258)">
The SIM refuses USSD actions. Reboot; if that does not help, escalate to the operator's network team.
</Accordion>
<Accordion title="No SMS is received">
Check the SIM's history in the platform: the SMS may simply have arrived after the timeout.
</Accordion>
<Accordion title="A call is emitted then suddenly stops">
Either the SIM has no airtime, or it is not allowed to call this number (short numbers, or unavailable while roaming).
</Accordion>
<Accordion title="A test fails with robot unreachable">
Either the robot is not connected ([a robot that stays Offline](/hardware/network-troubleshooting)), or, if the agent shows available in administration, the robot's clock is out of sync: ask support to check.
</Accordion>
</AccordionGroup>

## What's next?

<Columns cols={2}>
  <Card title="Swap a SIM" icon="sim-card" href="/hardware/swap-sim">

    Replace a SIM that turned out faulty

</Card>
  <Card title="USSD Command" icon="hashtag" href="/tests/actions/cellular/ussd">

    The session states a USSD test can assert on

</Card>
</Columns>