TOYOTA ELECTRONIC TRANSMISSION CHECKS & DIAGNOSIS
Checks and Adjustments
The transmission requires regular maintenance intervals if it is to continue to operate without
failure. As we discussed in previous sections, transmission fluid loses certain properties over
time and especially due to heat.
The Maintenance Schedules found in the repair manual or the Owners Manual indicate the
appropriate replacement schedules based on how the vehicle is used. Schedule A for example,
recommends replacement of the fluid every 20,000 miles or 24 months. Whereas Schedule B
recommends just an inspection of the fluid every 15,000 miles or 24 months and no
replacement interval.
The chart below indicates which maintenance schedule to follow based on the use of the
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TOYOTA ELECTRONIC TRANSMISSION CHECKS & DIAGNOSIS
The fluid level in the automatic transmission should be inspected by means of the dipstick after
the transmission has been warmed up to ordinary operating temperature, approximately 158'F
to 176'F. As a rule of thumb, if the graduated end is too hot to hold, the fluid is at operating
temperature. The fluid level is proper if it is in the hot range between hot maximum and hot
NOTE: The cool level found on the dip stick should be used as a reference only when the
transmission is cold. The correct fluid level can only be found when the fluid is hot.
It is important to keep the fluid at the correct level at all times to ensure proper operation of the
automatic transmission. If the fluid level is too low, the oil pump will draw in air, causing air to
mix with the fluid. Aerated fluid lowers the hydraulic pressure in the hydraulic control system,
causing slippage and resulting in damage to clutches and bands. If the fluid level is excessive,
planetary gears and other rotating components agitate the fluid, aerating it and causing similar
symptoms as too little fluid. In addition, aerated fluid will rise in the case and may leak from the
breather plug at the top of the transmission or through the dipstick tube.
In addition, be sure to check the differential fluid level in a transaxle. This fluid is sealed off and
separate from the transmission cavity in some applications.
Throttle Cable
The throttle cable is adjustable on all automatic transmissions. And in each case it controls
throttle pressure. Throttle pressure is an indication of load. When the throttle is depressed, the
cable transfers this motion to the base of the throttle valve and moves it upward to increase
throttle pressure. Throttle pressure causes the primary regulator valve to increase line
pressure. As the throttle is depressed, greater torque is produced by the engine and the
transmission may also downshift to a lower gear. If line pressure did not increase, slippage
could occur which would result in wear of the clutch plate surface material.
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