Automatic Transmission Diagnosis: Description
The A-343F automatic transmission is electronically controlled. Transmission shifting and torque converter lock-up are controlled by an Engine Control Module (ECM). Control module is a combined engine control and transmission control unit.
ECM receives information from various input devices and uses this information to control solenoids on transmission valve body for transmission shifting, torque converter lock-up and line pressure. Shift changes are performed by solenoids No. 1 and No. 2. Torque converter clutch lock-up is performed by SL solenoid. The SLT solenoid is used to modulate and generate line pressure according to accelerator pedal position or engine power output. Adjusting line pressure provides smooth transmission shifting.
A pattern select switch is located near shift lever on center console. Pattern select switch contains a POWER (PWR) and a NORMAL operating position. When pattern select switch is depressed (PWR position), transmission upshifts and downshifts will occur at a higher vehicle speed than with switch released. An indicator light on instrument panel indicates pattern select switch is in PWR (on) position. See Fig 1.
Pattern select switch also includes a 2nd start switch. When switch is activated, transmission will start out in 2nd gear. If gear selector is in "D" position, transmission will shift up through 3rd gear to OD. If transmission is in 2nd gear, transmission is held in 2nd gear.
An Overdrive (OD) switch is mounted on shift lever. See Fig 1. When OD switch is depressed to ON position, transmission will shift into 4th gear when shift lever is in "D" position, and OD OFF light on instrument panel will go off. When OD switch is released to OFF position, transmission will shift into 3rd gear, and OD OFF light will come on.
Transmission is equipped with a shift lock and key lock system. Shift lock system prevents shift lever from being moved from Park unless brake pedal is depressed. In case of a malfunction, shift lever can be released by depressing shift lock override button, located near shift lever. Key lock system prevents ignition key from being moved from ACC to LOCK position on ignition switch unless shift lever is in Park. For more information on shift lock and key lock system, see TOYOTA & LEXUS SHIFT LOCK SYSTEMS article.