A/T System Description - Electronic Control System

Electronic Control System

Electronic Control
The electronic control system consists of the powertrain control module (PCM),sensors, and the solenoid valves. Shifting and lock-up are electronically controlled for comfortable driving under all conditions.

Functional Diagram
The PCM receives input signals from the sensors, switches, and the other control units, processes data, and the outputs signals for the engine control system and the A/T control system. The A/T control system includes shift control, grade logic control, clutch pressure control, and lock-up control. The PCM switches the shift solenoid valves and the A/T clutch pressure control solenoid valves ON and OFF to control gear selection and the torque converter clutch lockup.





Shift Control
The PCM instantly determines which gear should be selected by various signals sent from sensors and switches, and it actuates shift solenoid valves A, B, C, and D to control gear selection.
The shift solenoid valves have two types:

^ Shift solenoid valves A and D use ON-OPEN/OFF-CLOSE type; the shift solenoid valve opens the port of shift solenoid valve pressure while the shift solenoid valve is turned ON by the PCM, and closes the port when shift solenoid valve is OFF.
^ Shift solenoid valves B and C use ON-CLOSE/OFF-OPEN type; the shift solenoid valve closes the port of shift solenoid valve pressure while the shift solenoid valve is turned ON by the PCM, and opens the port when shift solenoid valve is OFF.
The combination of driving signals to shift solenoid valves A, B, C, and D are shown in the table.





Shift Control - Grade Logic Control
The grade logic control system has been adopted to control shifting in D. To control shifting while the vehicle is ascending or descending a slope the PCM compares actual driving conditions with programmed driving conditions, based on the input from the accelerator pedal position sensor, the engine coolant temperature sensor, the barometric pressure sensor, the brake pedal position switch signal, and the shift lever position signal.





Grade Logic Control: Ascending Control
When the PCM determines that the vehicle is climbing a hill in D, the PCM extends the engagement area of 2nd gear, 3rd gear, and 4th gear to prevent the transmission from frequently shifting between 2nd and 3rd gears, between 3rd and 4th gears, and between 4th and 5th gears. The PCM does this so the vehicle can run smoothly and have more power when needed.





Grade Logic Control: Descending Control
When the PCM determines that the vehicle is going down a hill in D, the upshift speed from 4th to 5th gear, 3rd to 4th gear, and from 2nd to 3rd (when the throttle is closed) becomes faster than the set speed for flat road driving to extend the 4th gear, 3rd gear, and 2nd gear driving areas. This, in combination with engine braking from the deceleration lock-up, achieves smooth driving when the vehicle is descending. There are three descending modes with different 4th gear driving areas, 3rd gear driving areas, and 2nd gear driving areas according to the magnitude of a gradient stored in the PCM. When the vehicle is in 5th or 4th gear and you are decelerating while applying the brakes on a steep hill, the transmission will downshift to a lower gear. When you accelerate, the transmission will then return to a higher gear.





Clutch Pressure Control
The PCM actuates A/T clutch pressure control solenoid valves A, B, and C to control the clutch pressure. When shifting between gears, the clutch pressure regulated by A/T clutch pressure control solenoid valves A, B, and C engages and disengages the clutch smoothly. The PCM receives input signals from the various sensors and switches, processes data, and outputs current to A/T clutch pressure control solenoid valves A, B, and C.





Lock-up Control
Shift solenoid valve D controls the hydraulic pressure to switch the lock-up shift valve ON and OFF. When the PCM actuates shift solenoid valve D and A/T clutch pressure control solenoid valve C ON, and lock-up starts. A/T clutch pressure control solenoid valve C regulates and applies hydraulic pressure to the lock-up control valve to control the amount of lock-up. The lock-up mechanism operates in D (2nd, 3rd, 4th, and 5th gears), and in D with D3 driving mode (2nd and 3rd gears).

PCM A/T Control System Electrical Connections:

PCM A/T Control System Inputs and Outputs (Part 1):

PCM A/T Control System Inputs and Outputs (Part 2):

PCM A/T Control System Inputs and Outputs (Part 3):

PCM A/T Control System Inputs and Outputs (Part 4):