4T60 Automatic Transaxle

DESCRIPTION
The PCM controls automatic transmission shift points by use of solenoid operated fluid valves inside the transaxle. The solenoids get power when the ignition is "ON", and become energized when the PCM completes the circuit to ground.

OPERATION
When the transmission is placed in "D" range, the PCM energizes both shift solenoids to engage first gear. The PCM constantly monitors engine speed, vehicle speed and throttle position to determine shift points. When vehicle speed and throttle position sensor signals reach calibrated values, the PCM turns solenoid "A" off, forcing a shift to second gear (second gear - only solenoid "B" is energized). When a third gear shift is required, the "B" solenoid is turned "OFF" (third gear - solenoids "A" and "B" are "OFF"). In fourth gear, only solenoid "A" is energized. The PCM ignores all positions of the "PRNDL" switch except for manual low. When the gear selector is in the manual low position, the PCM will keep both solenoids "A" and "B" energized until the engine reaches 5,400 rpm, when the PCM will turn solenoid "A" off and force a first-second shift. This is to avoid engine and transmission damage.