CERTAIN MY 2004 THROUGH 2007 CE AND BE SCHOOL BUSES AND 1300 AND 3300 MODEL VEHICLE CHASSIS MANUFACTURED BY IC CORPORATION BETWEEN MARCH 17, 2004, AND MAY 15, 2006. THE PARK BRAKE SYSTEM MAY ACTIVATE WHILE THE VEHICLE IS UNDER NORMAL OPERATION. ALTHOUGH THE VEHICLE IS BROUGHT TO A STOP, THE ACTIVATION MAY OCCUR WITHOUT WARNING OR INPUT FROM THE DRIVER AND MAY STRAND THE VEHICLE IN AN ACTIVE LANE. THE SPRING APPLIED, HYDRAULIC RELEASE (SAHR) PARK BRAKE ACTUATOR COULD EXPERIENCE A HYDRAULIC LOCK CONDITION THAT WILL NOT ALLOW THE PARK BRAKE TO APPLY.