Description & Operation: Notes

The Hydra-Matic 4T45-E use 2 electronic shift solenoids, controlled by a Transmission Control Module (TCM), to control shifting and a pressure control solenoid to control hydraulic pressure. Torque Converter Clutch (TCC) solenoid is a Pulse Width Modulated (PWM) solenoid which controls TCC apply and release. Each solenoid is turned on or off by the TCM. TCM includes on-board self-diagnostics. This helps identify which components or circuits may need further testing.

Each solenoid either holds hydraulic pressure (solenoid on) or releases hydraulic pressure (solenoid off). This action controls shift valves inside valve body. By switching one or both solenoids on or off, different combinations of clutches, sprags and bands are operated. See SOLENOID POSITIONS  table. Line pressure is increased or decreased by TCM changing the duty cycle on pressure control solenoid.

Line pressure control system compensates for normal wear of transaxle components during upshifts in order to maintain optimal shift quality during life of transaxle. TCM uses "adaptive learning" to maintain acceptable upshift times by adjusting line pressure. TCM compares actual "acceptable" shift time to calibrated desired shift time and calculates difference. An "acceptable" shift is considered valid if no inconsistent vehicle operations (A/C compressor cycling or extreme throttle changes) occurred during upshift. Line pressure is either increased or decreased depending on duration of upshift time.