Foxflash read PSA MD1CS003 ECU fine but failed to write. Any solution?
Your battery is low. 12.1v on bench seems less to this ECU.
Better with 13.5V and 2-3A.
If still fails, fix checksum manually and write back.
If ECU is after 2020, it is not possible to remap that ECU (with OTP zone). You cannot read anything.