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Error codes › EMM cause (LTE NAS)

EMM cause #3 Illegal UE

EMM cause (LTE NAS)3GPP TS 24.301 §9.9.3.9 and Annex A

What it means

Illegal UE: the network considers the SIM invalid, typically after a failed authentication or a blacklisted identity. The UE treats the SIM as invalid until it's restarted.

Where you see it

In LTE NAS Attach reject, Tracking area update reject, Service reject or Detach request.

What to check

Check authentication (Ki/OPc) and whether the IMSI is barred in the HSS.

Look at the S6a (MME↔HSS) and S11 messages just before the reject: they usually show the real trigger.

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Related codes

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