Transmission Control Systems: Description and Operation

A/T Control System:

Input/Output Signal Of A/T Control Unit:

DESCRIPTION
The A/T control unit receives signals sent from various switches and sensors. The control unit then determines required line pressure, shifting point, lock-up operation, engine brake operation. The unit sends required signals to the respective solenoids.

FAIL-SAFE
The A/T control unit has an electronic Fail-Safe (limp home mode). This allows the vehicle to be driven even if a major electrical input/output device circuit is damaged.
Under Fail-Safe, the vehicle always runs in third gear with shift lever position of 1, 2 or D. Customer may say "Sluggish, poor acceleration".
When Fail-Safe operation occurs the next time the key is turned to the ON position, the power indicator lamp will blink for about 8 seconds.
Fail-Safe may activate without electrical circuit damages if the vehicle is driven under extreme conditions (such as excessive wheel spins and emergency braking immediately afterwards). In this case, turn key OFF for 3 seconds and then ON to recover normal shift pattern.
The blinking of the power indicator lamp for about 8 seconds will appear only once and be cleared. The customer may resume normal driving conditions by chance.