Street Smart - January/February - 2021

Toyota A340 Valve Bodies – In the Hunt for Fuel Milage…

The Toyota A340E transmission has been around since 1985. The transmission was used behind four- and six-cylinder engines. It is not uncommon for this transmission to go well over 150,000 miles without any problems. So it might be years later that you get the opportunity to see one in the shop. The most common problems on this transmission were a bad TPS sensor and overdrive planetary issues.

As with most transmission models, there are changes within the transmission.The A340 is no different. The valve body is the most common component updated and fairly easy to identify. The early valve bodies had one shift solenoid at the rear of the valve body. On the side of the valve body are one shift solenoid and one lock-up solenoid (figure 1).

This stayed that way for about 15 years until Toyota decided to make changes to help with fuel economy. In 2000, Toyota came out with a full-size truck with the 4.7L V-8. They did away with the TV cable and added the SLT solenoid (EPC) to offer a faster pressure control response (figure 2). They also mounted all the solenoids on the side of the valve body. The valve body on the four- and six-cylinder engines have two shift solenoids, a lock-up solenoid, and a TCC accumulator solenoid (figure 3).

In 2005 Toyota added a torque converter clutch pressure control modulated solenoid (SLU) in place of the on/off type solenoid (Figure 4). With this new solenoid, Toyota can control lock-up in several different modes. We can have a partial lock up depending on engine load or on deceleration and full lock up.

The torque converter lock-up is controlled by the ECM based on several inputs, including the following:

  • Turbine (input) speed sensor (NC0).
  • Output speed sensor (SP2).
  • Engine speed.
  • Engine load.
  • TPS.
  • Engine coolant temperature.
  • Vehicle speed.
  • Transmission fluid temperature.
  • Gear selection.

The ECM determines the torque converter’s lock-up status by comparing the engine speed with the input turbine speed and calculates the actual transmission gear.When the conditions are appropriate, the ECM commands lock-up by applying the control voltage to the shift solenoid SLU. When the SLU is turned on, the solenoid SLU applies pressure to the lock-up relay valve and locks the torque converter.

When you’re working on these older units, be cautious of updates… And that’s not just smart…

THAT’S STREET SMART!