Hydraulic Control System (A340F); Line Pressure (A340F); Throttle Pressure (A340F) - Toyota Hilux Surf 1993 Owner's Manual

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HYDRAULIC CONTROL SYSTEM
The hydraulic control system is composed of the oil pump, the valve body, the solenoid valves, and the
clutches and brakes, as well as the fluid passages which connect all of these components. Based on the
hydraulic pressure created by the oil pump, the hydraulic control system governs the hydraulic pressure
acting on the torque converter clutch, clutches and brakes in accordance with the vehicle driving condi–
tions.
There are three solenoid valves on the valve body. These solenoid valves are turned on the off by signals
from the ECM to operate the shift valves. These shift valves then switch the fluid passages so that fluid
goes to the torque converter clutch and planetary gear units.
(Except for the solenoid valves, the hydraulic control system of the electronic controlled transmission is
ba–
sically the same as that of the fully hydraulic controlled automatic transmission.)
• LINE PRESSURE
Line pressure is the most basic and important pressure used in the automatic transmission, because
it is used to operate all of the clutches and brakes in the transmission.
If the primary regulator valve does not operate correctly, line pressure will be either too high or too
low. Line pressure that is too high will lead to shifting shock and consequent engine power loss due
to the greater effort required of the oil pump; line pressure that is too low will cause slippage of
clutches and brakes, which will, in extreme cases, prevent the vehicle from moving. Therefore, if
either of these problems are noted, the line pressure should be measured to see if it is within stan–
dard.
• THROTTLE PRESSURE
Throttle pressure is always kept in accordance with the opening angle of the engine throttle valve.
This throttle pressure acts on the primary regulator valve and, accordingly, line pressure is regulated
in response to the throttle valve opening.
In the fully hydraulic controlled automatic transmission, throttle pressure is used for regulating line
pressure and as signal pressure for up–shift and down–shift of the transmission. In the electronic
controlled transmission, however, throttle pressure is used only for regulating line pressure. Conse–
quently, improper adjustment of the transmission throttle cable may result in a line pressure that is
too high or too low. This, in turn, will lead to shifting shock or clutch and brake slippage.
AUTOMATIC TRANSMISSION – Operation