the sequence of steps shown in fig7 a and 7b an initial step 523 resets bus_post_trip_lag_flag to ensure an additional iteration a following step 524 checks the status of bus_post_trip_timer_flag and bus_post_trip_alarm_timer if either bus_post_trip_timer_flag is not false or bus_post_trip_alarm_timer has not expired a step 525 is performed next however if both bus_post_trip_timer_flag is false and bus_post_trip_alarm_timer has expired a step 524 a is performed before step 525 step 524 a starts bus_post_trip_alarm_timer and sets bus_post_trip_timer_flag step 525 determines the status of both ignition switch 47 and the park brake switch if both the ignition switch is in accessory position and the park brake is being applied the algorithm determines the status of the disarming switch 45 s at the rear of the bus via a sequence of steps 526 527 and 528 if either the ignition switch is not in accessory position or the park brake is not being applied the algorithm sets the value of bus_post_trip_button_pushed_flag to 0 after either step 528 or step 529 the algorithm performs a step 530 the status of disarming switch 45 s is indicated by bus_post_trip_button_pushed_flag that can have any one of four unique values 0 1 2 or 3 bus_post_trip_button_pushed_flag is assigned the value 0 by the algorithm before the algorithm reaches step 525 step 526 checks the switch status to assure that bus_post_trip_button_pushed_flag has been reset to 0 and to assure that the disarming switch is not being actuated i e is off i e false this corresponds to the rear door lever being in position barring the rear door from opening when step 526 confirms that bus_post_trip_button_pushed_flag has been set to 0 and that disarming switch 45 s is off step 531 sets bus_post_trip_button_pushed_flag to the value 1 so long as disarming switch 45 s remains.