Function Of Ecm - Toyota Hilux Surf 1993 Owner's Manual

AT–50

FUNCTION OF ECM

• Control of Shift 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 accor–
dance 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 electroni–
cally 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. How–
ever, when the vehicle is being driven using the cruise control system (CCS), 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 prevent 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 70
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 (Nor–
mal or Power). Based on this lock–up pattern, the ECM turns lock–up solenoid valve on or off in accor–
dance with the vehicle speed signals received from the vehicle speed sensor and the throttle opening sig–
nals 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 disen–
gage 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.
1) The brake light switch comes on (during braking).
2) The IDL points of the throttle position sensor close (throttle valve fully closed).
3) The engine coolant temperature falls below 70
The purpose of 1) and 2) above is to prevent the engine from stalling if the rear wheels lock up. The pur–
pose 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 transmission 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.
AUTOMATIC TRANSMISSION – Operation
C (158
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C (158 F).
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F), preventing the transmission