The Catholic Church does not teach that sinners are saved by faith alone (sola fide).
The Pontificator, Al Kimel, explains why that statement is and ought to be true.
"You shall know the truth, and the truth shall make you odd." ~Flannery O'Connor
The Catholic Church formally teaches that sinners must earn their way into heaven through good works.
Al Kimel at Pontifications explains why that's a bad reason. A Lutheran minister responds here.