Sanders was fined $15,000 and the Steelers $35,000, the NFL said.
The league had told clubs in September it intended to crack down on faked injuries used to stop the clock or give a team a chance to get better organised.
Sanders grabbed his leg and fell to the ground complaining of a cramp during the fourth quarter of the Steelers' 24-17 win.
NFL executive vice president of football operations Ray Anderson said in a letter to Sanders and the Steelers, "neither the video sequence of the pertinent plays nor the observations of the on-field official support Sanders's contention that he was in severe pain."
After sitting out one play, Sanders returned to the field to help in coverage of a fourth-down punt and sprinted down the field ahead of all the other Pittsburgh players.
Anderson said there was no suggestion the Steelers had taught or condoned the faking of injuries.
"If I believed that to be the case, the discipline would be substantially more," he said.
