EC25 : Flow control RTS/CTS activation impossible

On the EC25-minipci modem ( Firmware : EC25EFAR06A17), I cannot activate RTS/CTS flow control.

AT+IFC=?
+IFC: (0.2),(0.2)

AT+IFC=2.2 //Open the hardware flow control
OK
AT+IFC?
+IFC: 0.0

This stays at the default values 0.0.

How do I activate flow control?

Dennis