I always assumed that after the Apollo Command Module separated from the Service Module, the SM was effectively inert and was simply left to re-enter of its own accord. However, from the Apollo 11 Flight Journal:
194:54:40 Aldrin: Houston, we got the Service Module going by. A little high and a little bit to the right.
194:54:49 Evans: Roger. Thank you.
194:54:53 Collins: And it's rotating just like it should be. Thrusters are firing.
It sounds like it's doing some sort of deliberate, powered maneuver for a controlled re-entry. What was that maneuver, and was it being initiated by the SM, ground control, or someone else entirely?