Description & Operation: Introduction

The 4F20E is a 4-speed transaxle assembly controlled by both electronic and mechanical systems utilizing a compound planetary gearset, gear drive, and an open differential. One band, 5 friction clutches, and 2 one-way clutches provide 4 forward gear ratios and reverse. Transaxle has 6 range positions, "P", "R", "N", "D", "2", and "1". Overdrive is manually controlled by a gearshift handle mounted switch.

Input signals from sensors, and Powertrain Control Module (PCM) are sent to the Transmission Control Module (TCM). The TCM can determine when the time and conditions are right for a shift or converter clutch application. The TCM can also determine line pressure needed to optimize shift feel.

Five electronic solenoids accomplish these functions; 2 On/Off solenoids for shifting, a Pulse-Width Modulator solenoid for torque converter clutch control, a Electronic Pressure Control (EPC) solenoid for line pressure control, and a coasting clutch solenoid to control the release of the coast clutch and the coordinated release of the direct clutch and apply of the 2-4 band. The TCM has built-in self-diagnosis, fail-safe code and warning code display for the main input sensors and solenoid valves.