Chart C-8B, 4T60 Transaxle Shift Solenoid Functional Check - 1991 E Body (Except ELDORADO) 3.8L PFI (VIN L): Notes
Fig 1: Chart C-8A, 4T60 Shift Solenoid Circuit Diagram (1991 E Body (Except Eldorado) 3.8L PFI VIN L)
The 4T60E transmission uses two solenoids to control shifting. Shift solenoid "A" and shift solenoid "B". See 4T60 SHIFT SOLENOID OPERATING SEQUENCE table for solenoid operating sequence.
PCM monitors TPS and vehicle speed versus engine speed to determine the correct shift points. If PRNDL position indicates manual low position, PCM will keep both solenoids energized until 54 RPM at which point PCM will force a shift by de-energizing solenoid "A". Manual 2nd and manual 3rd are controlled hydraulically within transmission.