Delivering the Goods - December - 2019

Toyota’s Aging Front Wheel Drive Six Speeds: Common Issues with the U660E and U760E Transmissions

The U660E first appeared in the Lexus ES350 and the Toyota Camry in 2007. Then it showed up in the 2008 Avalon, followed by the Venza in 2009. It is used behind the V-6 engines. The U760E was first used in model year 2010 for 4-cylinder application motors. These units have logged thousands of miles and have become more common in repair shops. As these units age, they are showing common issues. Here, we’ll take a look at these concerns along with diagnostic processes.

delivering the good figureDiagnostics

When diagnosing this transmission, it is extremely important to be aware that you are diagnosing the entire drivetrain management system. Scan all modules for codes! Record and fix these issues first. Beyond the basics, these units can present shift-quality and lock-up scheduling challenges that require going outside of the box.

We all know to use freeze frame data to help us duplicate the customer’s complaint when a code is present. However, Toyota gives us another diagnostic tool to assist in the process called “Check Mode”. Check Mode is a scan-tool-driven function that has been available since the 1996 model year. It places the TCM or PCM in a high-sensitivity mode for setting codes. When this mode is engaged, codes that may take two or more drive cycles will set immediately when the fault conditions are detected.

Before enabling Check Mode, record all stored trouble codes and freeze frame data. This information will be erased when the module is placed in Check Mode. Once you have finished diagnosing in this mode, you must exit Check Mode to return the module to normal operation.

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Harsh Coasting Down Shift Issues

These units commonly develop a harsh coasting downshift complaint with time. With higher mileage, drivability concerns start to come into play. The adaptive systems that are used in powertrain management programming make continuous adjustments to keep the engine and transmission running as designed, however, normal wear and tear can create situations that cannot be accounted for. While the subtleties are usually not noticed on the engine side, the transmission strategy is commonly affected.

When harsh coasting down shifts exist with no codes, check the mass air flow sensor and throttle body. When a Toyota comes in with a MAF code, there is at least a performance concern that you must address; even if the code clears and does not come back in Check Mode. Monitor MAF and TPS data in graph mode on your scan tool. Observe the MAF sensor rate of response especially when transitioning from open to closed throttle.

Inspect the throttle body. If it looks dirty or not, the air bleed passages and throttle blade surfaces will have carbon deposited on them. The manifold side of the throttle body will always be worse than the air box side (figure 1). This will directly affect the coast down strategy.

A carbon build up can obstruct the throttle blade, allowing too much air into the manifold. A “part-throttle” condition will cause the injectors to add fuel to compensate and prevent the engine from stalling. At the same time, the transmission pressure and shift strategy will respond as if the driver has their foot on the accelerator pedal. The result is firm or harsh downshifts.

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The Transmission Fluid

These units use the Toyota WS fluid. Using the correct fluid in these units is very important. Toyota seems to have gone to great lengths to mate the fluid to the coefficients of friction of the torque converter clutch as well as the individual clutch elements. To add another factor, the transmission pressure control strategy changes relative to the transmission fluid temperature. With all these variables in play, it would be difficult for a fluid dynamics specialist to match the formulation required to deliver proper performance from cold to hot.

The most common issues that arise from incompatible fluid usage are:

  • Torque converter clutch apply shudder.
  • Harsh or flaring shifts.
  • Shift and/or pressure solenoid performance codes.

If any of these conditions exist prior to a service or overhaul, servicing the fluid may correct the customer’s complaint.

Lock Up Apply Issues

The most common complaint with these units is a shudder sensation between 25mph to 50mph. The issue occurs under light to moderate throttle.

Many of these vehicles had TCC apply related issues while yet under warranty. Programming updates were made to address some of the concerns. Get as much vehicle and customer complaint history as possible. While lock up related issues are common with this unit, the causes can vary. Common issues are as follows:

  • Incorrect or deteriorated transmission fluid.
  • Failing torque converter
  • TCM programming, relearn adaptive values
  • Valve body and/or Lock Up solenoid hydraulic and/or mechanical performance.

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Toyota uses a strategy called “Flex Lock Up” to manage torque converter clutch apply and release. It is a partial lock up condition commanded during light to moderate throttle application. It can be commanded from first to 6th gear. Flex Lock up is based on torque demand, vehicle speed and other factors. It also operates while coasting or braking to keep engine speed low.

When diagnosing for a suspected TCC shudder complaint, use Manual 3rd gear. When the shift selector is in Manual 3, the Flex Lock up strategy is disabled. This will allow you to isolate possible engine related concerns relative to the complaint.

The Valve Body

Valve body wear is a growing concern with these units. It is a direct byproduct of pulse width modulated pressure management. Toyota uses pulse width modulation for main line pressure control, TCC apply, and clutch apply. It is only a matter of time that the critical control valve bores will suffer the consequences. There are 3 valves that must always be checked (figures 2A and 2B):

  • The Primary Pressure regulator valve
  • The Lock up Control and Lock up Control Boost valves
  • The Solenoid Modulator valve

There are several aftermarket solutions for valve body wear issues. Contact your soft parts supplier to get the product of your choice.

Toyota solenoids rarely fail electrically, however, they are prone to fail mechanically. Solenoid performance codes are the result. Of course, when a solenoid performance code is set, the related hydraulic and mechanical components must be verified before condemning the solenoid.

Fluid deterioration and contaminants cause the solenoids to fail mechanically. Assess solenoid replacement by considering mileage and fluid condition. Always consider the cost of a new valve body assembly with solenoid versus your intended repair.

U660E Case Bearing Bore Wear

The U660E is prone to case wear where the main gear train bearing support is mounted. This is attributed to high torque loads from a low first gear ratio and Toyota’s torquey V-6 engine. With higher mileage, unit centerline issues occur. As a result, internal bushing wear is common. In extreme cases, the torque converter input spline area can break away, causing a no move condition (figure 3).

The case and bearing are available from Toyota. There are several aftermarket resources that restore these cases as well. If the outer bearing race moves at all, the case will need to be repaired or replaced.

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The Transmission Control Module (U0402, Invalid Data Received-Transmission Control Module)

On the U660E models only, Transmission Control Module plugs directly into the transmission solenoid case connector and bolts to the unit (figure 4). The TCM’s are developing unique failure patterns, usually involving circuit performance related codes. For testing purposes, these modules are plug-and-play, therefore installing another module can easily identify if the TCM is the problem. Before placing a TCM into service, it is necessary to initialize a new (or good used) module by entering the unit compensation code using an appropriate scan tool.

The cause of failure is not clear. In the case of all module failures, ALWAYS use voltage drop testing to verify power and ground feeds while the module is loaded (KOEO and KOER).

Clearing Adaptive Values

The TCM memory is non-volatile, which means, the shift strategy will be retained even when the battery is disconnected or the module is removed. DO NOT attempt to clear the adaptive memory by detaching and crossing the battery terminals. This may cause damage to the TCM and/or other modules. You must have a scan tool that is capable of performing this function. Toyota calls this the “ECT Reset Memory Utility”. Always clear codes in all modules prior to initializing this function, even if no codes are present.

Here’s where it gets tricky. Some aftermarket scan tools will show the function to be available, however, when you initialize it, nothing actually happens! The easiest way to determine if the adapts cleared is to test drive the vehicle from cold to hot. If the shift quality remains the same as before the reset, then most likely your scan tool cannot perform this function.

If you possess a J2534 pass thru devise and a laptop computer, you can purchase a subscription for the Techstream Lite program from the Toyota OEM website at http://techinfo.toyota.com. Using the factory tool will ensure that you not only reset the transmission adapts, but you will also be able to install any updated programming for the module at no extra fee. You need to purchase the Professional Diagnostic subscription. At this time, it is available for $65 for 2-days. Once you purchase the subscription, you can use the program on an unlimited number of vehicles for the time purchased.

As state-of-the-art technology ages, unforeseen problems will arise. Typical rebuild and diagnostic procedures will need to be adjusted to locate and solve these problems. Being aware of this fact will help us to prepare for a fresh look at aging transmissions.