Today we will show you an easy way to fix the SIM card problem in Xiaomi Redmi Note 4. If you experience "No SIM card detected", but IMEI is fine, here's a solution that might suit you. It was originally tested on the latest Global Stable ROM ROM, but may also work on other ROM versions.
How to fix SIM card issue on Redmi Note 4
- Enter engineering menu by typing *#*#3646633#*#*
- Select “Network Selecting”.
- And change to “SIM1 – GSM/WSDMA (auto)”
Now the SIM card must be detected and working properly. You must have an IMEI working for this solution.
Source : https://xiaomifirmware.com