Active Yaw Control (AYC) is a performance drivetrain system that helps steer the car by sending torque to specific wheels. First made famous on rally-inspired cars, this system does not just brake the inside wheel during a slide. Instead, it uses a specialized rear differential with wet clutches to actively pump extra power to the outside wheel during a corner, pushing the car around the turn.
The system relies on sensors tracking steering angle, throttle position, and yaw rate. If you enter a sharp corner, the computer detects the steering input and clamps the outside axle's clutch. By spinning the outside wheel faster, it creates a turning force (yaw moment) that combats understeer, allowing you to carry more speed through corners.
Maintaining these systems requires specialized gear oil. The differential housing has separate chambers: one for the hypoid gears and another for the wet clutch plates. Putting the wrong fluid in the clutch chamber will ruin the plates, causing shuddering noises and system failure.