The first of the 8-speeds was the AA80E, which appeared in the Lexus GS 460 2008-11, Lexus IS F 2008-14, and Lexus LS 460 2007-14. That was followed by the AA81E, which showed up in the Lexus GS 350 2011-14, Lexus IS350/350C, and Lexus IS250/250C 2014-up.
These transmissions use two planetary gear sets to achieve eight speeds. The rear planetary is a Ravigneaux-type gear unit, which consists of pairs of sun gears (middle and rear) and planetary pinion gears (long and short) with different diameters within a single planetary assembly.
Both transmissions use a balance piston in the C1, C2, C3, and C4 clutches to provide responsive and smooth shifts (Figure 1a). Primarily during all of the shifts from 2nd to 8th. T he clutch application chart shows what’s happening to achieve each gear range, and can help you identify where to look for a problem (Figure 1b).
How it works isn’t anything new, but it is interesting. In addition to the original clutch pressure that is regulated by the valve body, the clutch engagement force during the shift is affected by the excess centrifugal fluid pressure that acts on the inside of the piston chamber, this is referred to as “chamber A”.
In order to eliminate the influence caused by the centrifugal fluid pressure, the canceling fluid pressure chamber (referred to as “chamber B”) is provided on the opposite side of chamber A. As a result, it provides responsive and smooth shifts (Figure 2).
SOLENOID IDENTIFICATION AND APPLY CHART
There are nine solenoids and one pressure switch found in the AA80E series transmission. The charts below will show which solenoids are normally vented (N/V) and normally applied (N/A) as well as which solenoid is on or off during shifts. The SL1 pressure switch is normally open, with pressure closes to ground (Figure 3).
LINE PRESSURE CONTROL
The line pressure is controlled by the SLT (line pressure control solenoid assembly). The SLT line pressure is controlled by the TCM/ECM based on engine load (Figure 4).
CLUTCH PRESSURE CONTROL
The TCM monitors the signals from various types of sensors, such as the Input Speed Sensor (NT) and Intermediate Speed Sensor (NC3), output sensor (SP2) allowing shift solenoid valve SL1, SL2, SL3, SL4, SL5, line pressure solenoid SLT and lock up solenoid SLU to control the clutch pressure with driving conditions (Figure 5).
Once you’ve determined which clutch or brake is at fault, you can aircheck that component (Figure 6). Regulate your air pressure to 25-30 PSI, so you don’t get a fault reading.
Listen for the clutch to engage while applying air to the piston hole. If the clutches pass the aircheck, examine the valve body for wear or stuck shift valves. If you find excessive leaking during your aircheck, you’ll probably be going inside.
Most shift concerns on this transmission are caused by valve damage, bore wear, and damaged solenoids (Figure 7A-B-C). If the shift valves are free and there are no signs of excessive bore wear, you’re probably looking at replacing solenoids. As usual, these solenoids are so finicky that any debris can cause a failure.
If it is determined to be internal, and you’re dealing with high mileage vehicles, it is common for the molded pistons to shrink over time. Plan on replacing the molded pistons, even if they feel soft.
This unit has only one sprag; refer to the illustration in figure 8 for proper rotation. Hold the rear planetary gear assembly and turn the one-way clutch. The one-way clutch should freely counterclockwise and lock when you try to turn it clockwise.
It’s a good idea to use genuine Toyota ATF-WS. ATF-WS isn’t compatible with T-IV or Dexron ATF.
REGISTRATION
After you’ve replaced or repaired the transmission, you’ll need to input the transmission compensation code (Figure 9) into the TCM. With the transmission installed, the Quick Response (QR) code label will be positioned where you won’t be able to read the code.
Always record the transmission compensation code or input it using the Techstream before installing the automatic transmission. If you’re replacing the TCM, you’ll have to input the existing transmission compensation code into the new TCM. (Refer to the procedures in my GEARS article December 2015).
Repeat the road test patterns until the shift shock and engine speed overrun (shift flare) reach an acceptable level. When repeating the acceleration/ deceleration cycle of a road test pattern, bring the vehicle to a complete stop before accelerating again. Now you know how to learn the TCM, and that’s not just smart, that’s street smart!
