Transmission Control Systems: Description and Operation

GENERAL DESCRIPTION
The Electronically Controlled Automatic Transmission (4EAT) features a combination of electronic and mechanical systems for controlling forward gear shifting, torque converter lockup, and self-diagnosis capability to aid diagnostic procedures. A manual switch is provided for slow driving on steep, slippery, or dangerous roads.

MECHANICAL FEATURES
These include a single compact combination-type planetary gear (4 speed capability). There is also a variable-capacity oil pump providing a constant oil quantity at and above medium speeds. This reduces power loss from pumping more oil than necessary at higher speeds.

ELECTRONIC SYSTEM
The electronic system controls transmission shifting in forward speeds and torque converter lockup by means of solenoid operated valves. When energized, these valves actuate friction elements (clutches and bands) to control shifting in the planetary gear. Shift timing and lock up events are regulated by the control unit in programmed logic and in response to input sensors and switches.

4EAT diagnostic procedure, following a visual inspection for obvious defects and a Quick Test for service codes, consists of conducting either Pinpoint Tests or operational tests, or both, in logical sequence.

4EAT SYSTEM ELECTRONIC COMPONENTS

^ 4EAT Control Unit
^ Vehicle Speed Sensor (Input)
^ Pulse Generator (Input)
^ Throttle Position Sensor (Input)
^ Idle Switch (Input)
^ Coolant Temperature Switch (Input)
^ ATF Fluid Temperature Switch (Input)
^ Brake Light Switch (Input)
^ Neutral Safety Switch (Input)
^ Manual Switch (Input)
^ Solenoid Valve 1 - 2 Shift (Output)
^ Solenoid Valve 2 - 3 Shift (Output)
^ Solenoid Valve 3 - 4 Shift (Output)
^ Solenoid Valve Lockup (Output)