Electronic Control System

ELECTRONIC CONTROL SYSTEM
The electronic control system, which controls the shift points and the operation of the lock-up clutch, is composed of the following three parts:
1. Sensors
These sensors sense the vehicle speed, throttle opening and other conditions and send these data to the ECM in the form of electrical signals.
2. ECM
The ECM determines the shift and lock-up timing based upon the signals from sensors, and controls the solenoid valves of the hydraulic control unit accordingly.
3. Actuators
These are three solenoid valves that control hydraulic pressure acting on the hydraulic valves to control shifting and lock-up timing.

FUNCTION OF ECM
Control of Shifting Timing:
The ECM has programmed into its memory the optimum shift pattern for each shift lever position (D, 2. L position) and driving mode (Normal or Power).
Based on the appropriate shift pattern. the ECM turns No.1 and No.2 solenoid valves on or off in accordance with the vehicle speed signal from the vehicle speed sensor and the throttle opening signal from the throttle position sensor. In this manner, the ECM operates each shift valve, opening or closing the fluid passages to the clutches and brakes to permit up-shift or down-shift of the transmission.

HINT: The electronic control system provides shift timing and lock-up control only while the vehicle is traveling forward. In REVERSE, PARK, and NEUTRAL, the transmission is mechanically, not electronically, controlled.

Control of Overdrive:
Driving in overdrive is possible if the O/D main switch is on and the shift lever is in the D position. However, when the vehicle is being driven using the cruise control system (COS), if the actual vehicle speed drops to about 4 km/h (2 mph) below the set speed while the vehicle is running in overdrive, the CCS ECU sends a signal to the ECM to release the overdrive and prevents the transmission from shifting back into overdrive until the actual vehicle speed reaches the speed set in the CCS memory.
On this model, if the engine coolant temperature falls below 60°C (140°F), the ECM sends a signal to the ECM, preventing the transmission from up-shifting into overdrive.
Control of Lock-Up System:
The ECM has programmed in its memory a lock-up clutch operation pattern for each driving mode (Normal of Power). Based on this lock-up pattern, the ECM turns the lock-up solenoid valve on or off in accordance with the vehicle speed signals received from the vehicle speed sensor and the throttle opening signals from the throttle position sensor.
Depending on whether lock-up solenoid valve is on or off, the lock-up relay valve performs changeover of the fluid passages for the converter pressure acting on the torque converter clutch to engage or disengage the lock-up clutch.
Mandatory Cancellation of Lock-Up System:
If any of the following conditions exist, the ECM turns off lock-up solenoid valve to disengage the lock-up clutch.
- The brake light switch comes on (during braking).
- The IDL points of the throttle position sensor close (throttle valve fully closed).
- The vehicle speed drops 4 km/h (2 mph) or more below the set speed while the cruise control system is operating.
- The engine coolant temperature falls below 60°C (140°F) and vehicle speed is under 60 km/h (37 mph), or 35°C (95°F) and vehicle speed is under 40 km/h (25 mph).
The purpose of 1) and 2) above is to prevent the engine from stalling if the rear wheels lock up. The purpose of 3) is to cause the torque converter clutch to operate to obtain torque multiplication. The purpose of 4) is both to improve general driveability, and to speed up engine warm-up. Also, while the lock-up system is in operation, the ECM will temporarily turn it off during up-shift or down-shift in order to decrease shifting shock.