The AC60 transmission is Toyota’s answer to providing its rearwheel drive vehicle line with a lightweight but sturdy option for light to medium-duty applications. Its ability to handle considerable torque but require minimal horsepower makes it an excellent unit behind its four- and six-cylinder gas and diesel motors. This unit has been in the US and other world markets for about a decade. The transmission has proven durable; however, some concerns are worthy of mention. In this article, we will explore issues, causes, and fixes for this unit, as well as some diagnostic strategies to help you identify root-cause problems.
UNIT IDENTIFICATION
The AC60 transmission first appeared in the US market behind the 2.7L gas motor in the Toyota Tacoma. 2019 and later Landcruiser applications are now equipped with this unit as well (Figure 1). The unit comes in a 4WD (AC60F) or 2WD (AC60E) configuration, as well as regular or heavy duty. Use the transmission case label to properly identify the application you are working on (Figure 2). Note that heavy-duty applications generally have extra steel and friction per clutch pack.
UNIT OPERATION
Toyota uses four full-flow solenoids to control the individual clutch packs within the unit. The transmission utilizes clutch-to-clutch shifting, which relies on precise release and apply rates for smooth, seamless shifting. A turbine shaft and output speed sensor are used for TCM feedback to verify that range changes occur as commanded. Two internal transmission fluid temperature sensors are used for pressure management and emergency command strategy. Various sensors outside the transmission provide additional functional data via the vehicle CAN bus system.
DRIVABILITY COMPLAINTS
Drivability is one of the most common concerns with vehicles equipped with the AC60 transmission. These units are calibrated from the factory to shift into high range and lock up as soon as possible. The programming is intended to provide the best possible fuel economy. However, the engine’s performance feels sluggish at light to moderate throttle. Toyota has provided updated programming for the TCM to remedy this issue in most models. Check for bulletins on the Toyota website for your specific application.
FAILURE MANAGEMENT MODES
While full-flow solenoids offer an optimal way of controlling shift quality and timing, they require a failsafe strategy for managing issues. The strategy is activated only if the solenoid is “stuck OFF.” When a shift solenoid is stuck ON, power is cut to the faulty solenoid. When the TCM detects a solenoid fault, the following strategies are used to allow the vehicle to operate:
Shift Solenoid Valve SL1 Failure
Without Failsafe Strategy:
- If SL1 fails ON, the transmission will shift only the first through fourth gears (no fifth or sixth gears).
- If SL1 fails OFF, the transmission will shift to NEUTRAL in 1st through 4th gears. Only 5th and 6th gears will function.
With Failsafe Strategy:
- If SL1 fails OFF, the transmission will operate only in the 3rd or 5th gears.
Shift Solenoid Valve SL2 Failure
Without Failsafe Strategy:
- If SL2 fails ON, the transmission will shift to 4th gear in 1st through 4th gears. 5th and 6th gears will operate normally.
- If SL2 fails OFF, the transmission will shift normally from 1st through 4th gears and to NEUTRAL in 5th and 6th gears.
With Failsafe Strategy:
- If SL2 fails OFF, the transmission will only operate in 2nd and 3rd gears.
Shift Solenoid Valve SL3 Failure
Without Failsafe Strategy:
- If SL3 fails ON, the transmission will start in 2nd gear. 3rd through 6th gears will function normally.
- If SL3 fails OFF, the transmission will start in 1st but skip 2nd gear. 3rd through 5th will function normally. 6th gear will go to NEUTRAL.
With Failsafe Strategy:
- SL3 fails OFF, the transmission will operate in 3rd gear only.
Shift Solenoid Valve SL4 Failure
Without Failsafe Strategy:
- If SL4 fails ON, the transmission will start in 3rd gear and shift to 4th and 5th gears only.
- If SL4 fails OFF, the transmission shift pattern will be 1-2-1-4-NEUTRAL-6.
With Failsafe Strategy:
- If SL4 fails OFF, the transmission will operate in 2nd gear only.
It is essential to know that these strategies are commanded. Often, a customer may bring a vehicle in with a complaint directly related to these conditions. Remember that the vehicle may need to be driven for a while before a DTC is stored while a failure strategy is commanded.
SPEED SENSOR FAILURE
The AC60 has two external speed sensors (Figure 3). If a transmission speed sensor signal is lost, the ECU will default to a different sensor to reference to continue operating the transmission. However, adaptive functions and TCC strategies will be frozen until the signal is restored. If the Transmission Revolution sensor (NT) (ISS) fails, shift control is performed based on the transmission revolution sensor (SP2) (OSS) signal.
If the Transmission Revolution sensor (SP2) (OSS) fails, shift control is performed based on the wheel speed sensor signal. So, if shift quality or TCC-related issues persist after driving, monitor speed sensor data in TCM PIDs for possible issues first.
TRANSMISSION FLUID TEMPERATURE SENSORS
There are two holes in the valve body for the dual temperature sensors on the AC60 (Figure 4). ATF temperature sensor No.1 (THO1) is used for hydraulic pressure control. This sensor is used to revise the applied pressure to clutches and brakes in the transmission for smooth shift quality. ATF temperature sensor No.2 (THO2) is used to modify the ECT shift timing control when the ATF temperature is high. It is also used for the ATF temperature warning light.
The unit will not command 5th and 6th gears if either temperature sensor fails. Use scan data and a thermal temperature gun to determine proper sensor operation.
FLUID SERVICING ISSUES
An improperly performed fluid service will cause drivability issues with the AC60 unit. Toyota requires WS fluid to be used in this application. Setting the correct fluid level is critical. Several vehicle applications that use this unit have an auxiliary cooling system.
The AC60 uses a warmer and a control manifold with an integral thermal bypass valve. Proper service of the fluid requires fluid to flow through the entire cooling system, including the auxiliary cooler.
The transmission fill procedure is as follows:
- Use compressed air to blow dust off the thermostat cap and clean it.
- Using a screwdriver, push the shaft of the thermostat until the screwdriver contacts the step inside the cap.
- With the thermostat shaft pressed, push a pin (diameter: 1.0–1.8 mm [0.039”–0.070”]) into the hole on the side of the thermostat cap (Figure 5). Slide the pin in until it passes through the hole on the other side of the thermostat cap to fix the shaft in place.
- Fill the transmission with the amount of fluid listed by application.
- Allow the transmission fluid temperature sensor to reach 102-120°F (39-49°C) and check the level. If no fluid comes out, add 1/2 quart at a time and recheck. A trickle indicates the correct level.
- Reinstall the refill plug.
After completing the service, an additional TCM procedure is performed.
ATF THERMAL DEGRADATION INDICATOR
The TCM has a calculated monitor for the condition of the transmission fluid. The ATF Thermal Degradation Indicator uses various factors, such as vehicle mileage, actual engine run time, engine load history, transmission and coolant temperature history, and other parameters, to calculate the relative depletion of the transmission fluid. An arbitrary number is assigned to the relative wear on the fluid. The ATF Thermal Degradation Indicator range is zero to 65,535.
Use the Techsteam scan tool or an appropriate aftermarket tool to view and reset this value. If the value is 50,000 or more, the transmission fluid must be serviced. A valid fluid service requires 50% or more of the transmission fluid to be exchanged. Perform the ATF Thermal Degradation Estimate Reset after replacing the ATF or after a transmission overhaul.
If either of the following conditions is met, perform ATF Thermal Degradation Estimate Resetas follows:
- Connect the Techstream or equivalent scan tool to the DLC3.
- Turn the ignition switch ON. NOTICE: Do not start the engine!
- Turn the Techstream on.
- Enter the following menus: Powertrain / Engine and ECT / Utility / ATF Thermal Degradation Estimate Reset.
Note that other OE manufacturers use this counter to alter the transmission shift strategy as the fluid nears the end of its service life. At the time of printing this article, information was not found indicating this is the case with Toyota. However, failure to perform a reset may result in an OEM warranty claim rejection.
C1 CLUTCH DRUM FAILURE
The C1 clutch is the input or forward clutch. Its stamped steel design is similar to that of previous Toyota units. This drum can fail due to line pressure spikes caused by a worn valve body or extended operation in failsafe pressure mode (Figure 6). Carefully inspect this part for cracks or damage. Aftermarket replacements are available.
As newer units enter our shop, it is good to know common complaints and patterned failures before you dive into diagnosing. Knowledge helps minimize surprises and allows us to develop an intelligent approach to finding customer complaints. GEARS magazine aims to keep you in the know so you can deliver the goods to your customers with confidence!
