Fail Safe Operation

4. Fail-safe Function
The fail-safe control function ensures minimum level of driveability even if a fault should occur in the vehicle speed sensors, throttle position sensor, inhibitor switch, or any of the solenoids.
^ FRONT AND REAR VEHICLE SPEED SENSORS
A dual speed-sensing system is used. The speed signal is taken from the transmission (by the output shaft speed sensor). Even if one sensor system fails, the vehicle can be controlled normally with the other normally operating sensor system.
If both the front and rear vehicle speed sensors become faulty, the vehicle is made to operate only in the 1st and 3rd speeds.
^ THROTTLE POSITION SENSOR
If the throttle position sensor becomes faulty, the throttle opening is fixed at the predetermined angle.
^ INHIBITOR SWITCH
If the TCM receives different signals simultaneously from a faulty inhibitor switch, it selects a range in the following priority:
D > N (P) > R > 3 > 2 > 1 >
^ SHIFT SOLENOID 1 AND 2
If a fault occurs in either of solenoids 1 and 2, both the solenoids are de-energized, and the gear is held in the 3rd.
If both the solenoids should fail, the TCM invariably selects and keeps the 3rd gear.
^ LINE PRESSURE DUTY SOLENOID
If the line pressure duty solenoid fails, the solenoid is de-energized and the line pressure is raised to the maximum to enable the vehicle to operate.
In this condition, the usable gears are limited to the 1st and 3rd.
^ LOCK-UP DUTY SOLENOID
If the lock-up duty solenoid fails, the solenoid is de-energized and the lock-up clutch is disengaged.
^ TRANSFER DUTY SOLENOID
When the transfer duty solenoid becomes faulty, it is de-energized. This causes maximum oil pressure to be applied to the transfer clutch so that the power is always transmitted to the rear axle (direct-coupled AWD condition).
^ 2-4 BRAKE DUTY SOLENOID
If a fault occurs in the 2-4 brake duty solenoid, the solenoid is de-energized and the usable gears are limited to the 1st and 3rd.
^ LOW-CLUTCH TIMING SOLENOID
If a fault occurs in the low clutch timing solenoid, the solenoid is de-energized and the usable gears are limited to the 1st and 3rd.
^ 2-4 BRAKE TIMING SOLENOID
If a fault occurs in the 2-4 brake timing solenoid, the solenoid is de-energized and the usable gears are limited to the 1st and 3rd.
^ TORQUE CONVERTOR TURBINE SPEED SENSOR
If a fault occurs in the torque converter turbine speed sensor, the usable gears are limited to the 1st and 3rd.