Street Smart - April - 2023

The UA80E: A Closer Look at the 8-Speed Front-Wheel Drive for Toyota and Lexus

The UA80E first showed up in 2017. It was used from 2017 through 2022 in the Toyota Highlander with 2.5L and 3.5L engines. From 2018 through 2022, it came in the Toyota Camry 3.5L and Rav 4 with a 2.5L all-wheel-drive model. From 2019 through 2022, it came in the Toyota Avalon 3.5L and the Lexus ES300. And finally, you’ll find it in the 2020 Toyota Sienna with the 3.5L engine.

So, these vehicles have been on the road for almost six years and will begin showing up in your shops. Knowing where to start and what to check in diagnostics will be a great help.

Like everything today, you’ll want to start by checking for codes. Depending on what codes you have (if any), you will need to follow the diagnostic procedure for that code. Next, let’s check the fluid level.

To accurately check the fluid level, the factory recommends that fluid temperatures be at least 20°C (68° F), With the engine running in park. Now remove the bottom plug; fluid should just drip out of the hole (figure 1). If the fluid is low, add fluid slowly into the transmission fill hole (figure 2) until the fluid drips from the bottom plug. Depending on the complaint, you may want to check line pressure.

The UA80E has two pressure check locations, one for forward ranges and one for the reverse (figures 3 & 4). Forward pressure (with the engine idling) should be 73 to 102 PSI. The pressure should be 189 to 232 PSI during a stall test. In reverse (and the engine idling), you should have 73 to 102 PSI. The pressure should be 247 to 305 PSI during a stall test.

After checking the pressure, we can evaluate what the conditions are. If the pressure reads high in all positions, then possible causes can be the SLT solenoid valve is defective or the pressure regulator valve is sticking.

If the pressures are low in all positions, then possible causes can be that the SLT solenoid is defective, the pressure regulator valve is sticking, or a defective oil pump. If the pressure only reads low in the drive position, you could have a fluid leak in the number one clutch (C1), or the Number 2 Brake (B2).

If line pressure is low when the shift lever is in reverse only, then you may have a leak in the number 3 clutch (C3) or number two brake (B2).

One thing I like about this unit is that it has no sprags or bands. It utilizes four clutch packs and two brakes. It shifts from clutch to clutch, as seen in the clutch apply chart (figure 5). Each gear has two components on (and four off). This makes it simple as to what clutch or brake is at fault.

The UA80E transmission uses two Ravigneaux-type planetary gear sets to produce eight gears.

The UA80E uses a centrifugal fluid pressure canceling piston in the C1, C2, C3, and C4 clutches. A more general term used for these are balance pistons. They aid in releasing the clutch and ensuring that oil trapped on the apply-side does not partially apply the clutch while it is commanded off. It also helps control the apply rate of the clutch relative to powertrain demand.

In addition, the grooves in the clutches linings are designed to reduce drag when they’re off. Make sure the clutches you use to rebuild this unit have clutch lining grooves that match the original design. Failure to do so will result in shift quality issues.

Another fuel-economy feature is that the torque converter will apply in any gear (including first) based on the driving conditions.

Next, we want to look at the solenoid applied chart with the solenoid functions. (figures 6 & 7). Rather than operating a valve to deliver oil to each clutch, each solenoid delivers oil directly. The shift solenoids are called Direct Acting solenoids. This reduces the number of valves in the valve body and helps make diagnosis easier. They all rely on the SLT solenoid (for mainline pressure control), which is why checking line pressure is an important test for any shifting complaint. The converter clutch solenoid is on-off.

Lock-up is controlled by the SL and SLU soleonids. The SL solenoid is an on-off type that directs oil to a relay valve to enable the lock-up hydraulic circuit. The SLU is responsible for the rate of apply and release of the torque converter clutch.


The valve body must be removed to service the solenoids. Remove the nine bolts marked with an X, then remove the valve body.

Depending on the codes you have or the results of your pressure test, you can now replace any solenoids that may be bad. The one I see with the most problem is the SLT solenoid (line pressure control). It gets the most use and is a common cause of transmission failure. If you’re rebuilding one of these, consider replacing it, regardless of why the transmission failed. When this solenoid fails, you can end up with codes for other solenoids that are not really at fault but don’t have the pressure to do what they are supposed to (which I call ghost codes).

There’s lots more to come on this unit. Wait until you see the valve body breakdown in the next issue of Gears Magazine.

And that’s not just smart. That’s street smart.