what could be the problem with the ftp sensor.

More likely the circuit//wiring to the FTP sensor or another problem with tank venting in EVAP system!!.. **To help prevent guessing at it**... need exact code number(s).. FTP sensor is a very reliable part thar RARELY fails.... Any work been done recently around the gas tank area ?

May want to replace your gas cap. Lot of times if the wrong gas cap is on it or it is worn out it will cause emissions problem. I know it happened on my truck and I replaced the gas cap and it solved my problem. May want to try that first