General System Description

GENERAL SYSTEM DESCRIPTION
The A246E is an electronically controlled, lock-up type automatic transaxle with 4 forward speeds. Forth gear has an overdrive gear ratio of 0.981:1.
Electronic control is provided by an integrated powertrain control module (ECM) using Toyota Computer Control System (TCCS).

ELECTRONIC CONTROL SYSTEM



The electronic control system, which is controls the shift points and the operation of the lockup clutch, is composed of the following three parts:
(1) Sensors
These sensors sense the vehicle speed, throttle opening and other conditions and send this data to the ECM in the form of electrical signals.
(2) Electronic Control Module (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
There are three solenoid valves that control hydraulic pressure acting on the hydraulic valves to control shifting and lock-up timing.

FUNCTION OF ENGINE CONTROL MODULE (ECM)

ECM Transmission Control Connections:

^ Control of Shift Timing
The ECM has programmed into its memory the optimum shift pattern for each shift lever position (D, 2, L position).
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-shifting or down-shifting of the transaxle.
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 transaxle 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 (CCS), if the actual vehicle speed drops to about 10 km/h (6 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 prevent the transaxle from shifting back into overdrive until the actual vehicle speed reaches the speed set in the CCS memory.
On this model, if the coolant temperature falls below 55°C (131°F), the ECM prevents the transaxle from up-shifting into overdrive.

^ Control of Lock-up System
The ECM has programmed in its memory a lock-up clutch operation pattern. Based on this lock-up pattern, the ECM turns 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.
- This is to prevent the engine from stalling if the front wheels lock up.
^ The coolant temperature falls below 55°C (131°F).
- This is 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 upshift or down-shift in order to decrease shifting shock.

On-Board Diagnostics
The Electronically Controlled Transaxle has built-in self-diagnostic functions. If the malfunction occurs in the system, the ECM stores the diagnostic trouble code in memory and the "O/D OFF" (Overdrive OFF) indicator light blinks to inform the driver.

NOTE: This vehicle uses the Toyota Computer Controlled System (TCCS) which uses an integrated electronic powertrain (engine and transmission) control unit employing separate microprocessors for each function.
The diagnostic system's monitoring and code assignment ability is limited to opens or shorts in the Solenoid circuits and Speed Sensor circuit.

FAIL-SAFE MODE PARAMETERS
If either solenoid valve circuit develops a short or open, the engine control module (ECM) turns the remaining solenoid valve ON or OFF to allow the vehicle to be operated safely.

NOTE:
^ In the event of malfunction of either solenoid No.1 or No.2, the ECM turns OFF current to solenoid No.3 to disable torque converter lock-up.
^ In the case of a short circuit, the ECM stops sending current to the shorted solenoid.

Shift scheduling will be adjusted as shown in the following table.

Fail-Safe Mode Shift Functions:

NOTE: In the event of complete failure of the electronic control system, the transaxle will be unable to shift automatically but the driver may affect gear changes by manually shifting the gear selection lever. The gears available at each gear selector position in this condition are given in the right column of the previous image.