Transmission Control Systems: Description and Operation

Previous automatic transmissions have selected each gear shift using mechanically controlled throttle hydraulic pressure, governor hydraulic pressure and lock-up hydraulic pressure. The electronically controlled transmission, however, electrically controls the governor pressure and lock-up through the solenoid valve. Control of the solenoid valve by the engine control module based on the input signals from each sensor makes smooth driving possible by shift selection for each is most appropriate to the driving conditions at that time.

1. GEAR SHIFT OPERATION
During driving, the engine control module selects the shift for each gear which is most appropriate to the driving conditions, based on input signals from the engine coolant temp. sensor to TERMINAL THW of the engine control module and also the input signals to TERMINAL SP2+ of the engine control module from the vehicle speed sensor devoted to the electronically controlled transmission. Current is then output to the electronically controlled transmission solenoid.

When shifting to 1st speed, current flows from TERMINAL S1 of the engine control module to TERMINAL 1 of the electronically controlled transmission solenoid to GROUND, and continuity to the no. 1 solenoid causes the shift.

For 2nd speed, current flows from TERMINAL S1 of the engine control module to TERMINAL 1 of the electronically controlled transmission solenoid to GROUND, and from TERMINAL S2 of the engine control module to TERMINAL 2 of the electronically controlled transmission solenoid to GROUND. And continuity to solenoid no. 1 and no. 2 causes the shift.

For 3rd speed, there is no continuity to no. 1 solenoid, only to no. 2 causing the shift. Shifting into 4th speed (Overdrive) takes place when there is no continuity to the either no. 1 or no. 2 solenoid.

2. LOCK-UP OPERATION
When the engine control module judges from each signal that lock-up operation conditions have been met, current flows from TERMINAL SL of the engine control module to TERMINAL 3 of the electronically controlled transmission solenoid to GROUND, causing continuity to the look-up solenoid and causing lock-up operation.

3. STOP LIGHT SW CIRCUIT
If the brake pedal is depressed (Stop light SW ON) when driving in lock-up condition, a signal is input to TERMINAL STP of the engine control module, the engine control module operates and continuity to the look-up solenoid is cut.

4. OVERDRIVE CIRCUIT
* O/D main SW ON
When the O/D main SW is tuned ON, a signal is input to TERMINAL OD2 of the engine control module and engine control module operation causes gear shift when the conditions for overdrive are met.

* O/D main SW OFF
When the O/D main SW is turned to OFF, the current flowing through the O/D OFF indicator flows through the O/D main SW to GROUND, causing the indicator light to light up. At the same time, a signal is input to TERMINAL OD2 of the engine control module and engine control module operation prevents shift into overdrive.

5. A/T OIL TEMP. WARNING
When the A/T fluid temp. sensor affixed to the transmission case detects that the fluid temp. is 150° C (302° F) or more, the engine control module operates and the current flowing through the GAUGEfuse flows to the A/T oil temp. warning light to TERMINAL OIL-W of the engine control module to GROUND, so that warning light lights up, informing that the A/T oil temp. is high. When the A/T oil temp. drops to 120° C (248° F) or less, the engine control module stops operating and the warning light goes out.