Spaceflightnow is carrying this new update on recent developments with the Mars rover Spirit. It seems there's a problem with two of the drive wheels, which did not respond properly in a recently commanded maneuver. The current suspect is the steering actuator motor on each wheel, which is used to (duh) steer the wheel independently of the motor that drives it. If it turns out to be unfixable, engineers say they can command the rover to blow the fuses on the relays for the motors. While it will definitely release the brakes, it will also make the rover harder to steer.