Diagnosis - A-650E: Description: Introduction

Automatic transmission is electronically controlled. Transmission shifting and torque converter lock-up are controlled by an Electronic Controlled Transmission (ECT) Electronic Control Unit (ECU). Control unit is referred to as the ECT ECU. ECT ECU is combined with engine ECU into one unit.

ECT ECU receives information from various input devices and uses this information to control shift solenoids for transmission shifting and lock-up solenoid (also called SL or SLU solenoid) for torque converter lock-up. SLN solenoid is used to control hydraulic pressure acting on accumulator control valve. Valve assists in smooth shifting. Solenoids are mounted on transmission valve body. See Fig 1.

A pattern select switch is located near shift lever on center console. Pattern select switch contains a POWER (PWR), NORMAL and SNOW operating positions. When pattern select switch is depressed to 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. When pattern select switch is depressed to SNOW position, transmission starts out in 2nd gear.

An Overdrive (OD) switch is mounted on the shift lever. When OD switch is depressed to ON position, transmission will shift into 5th 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 4th gear, and OD OFF light on instrument panel will illuminate.

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 appropriate SHIFT LOCK SYSTEM article.