Fitted to versions 4 and above, Active Yaw Control pumps are known to fail on Evos after only a few years. They are used to pump the fluid used by the clutch pack on the rear axle to improve cornering speeds under acceleration. The AYC system sends torque to each of the rear wheels using ABS and G sensors to allow faster cornering. If your AYC light stays illuminated on the dash after you start the car, you probably need a replacement pump as the AYC system will not be functioning. These tend to go for around £200 to £250 and will cost an hours labour to fit at a garage.