Automatic Transmission Overhaul - M5DA: Operation

Shift lever has 7 positions. When shift lever is moved, manual valve on main valve body is moved by the shift cable. Shift lever also changes position of A/T gear position switch, mounted on the shift lever. The A/T gear position switch delivers an input signal to the PCM to indicate shift lever position. The PCM uses this input signal to control shift control solenoid valves. The PCM determines appropriate shift point and activates proper shift control solenoid valve for transaxle shifting.

When transaxle gear combinations are engaged by clutches, power is transmitted from mainshaft to countershaft to provide different gears. Shift lever positions operate as follows:

• "P" (Park)
  
  Front wheels lock as parking pawl engages with parking gear on countershaft. All clutches are released. Neutral position switch, incorporated in A/T gear position switch, allows engine starting in this position.
• "R" (Reverse)
  
  Reverse clutch is engaged. Back-up light switch, incorporated in A/T gear position switch, allows back-up lights to operate.
• "N" (Neutral)
  
  All clutches are released. Neutral position switch, incorporated in A/T gear position switch allows engine starting in this position.
• "D4" (Drive)
  
  Transaxle starts in 1st gear and upshifts automatically to 2nd, 3rd and then 4th gear. Transaxle will downshift through 3rd, 2nd and 1st gears until vehicle stops. When in 2nd, 3rd or 4th gear in this range, PCM sends a signal to operate torque converter lock-up.
• "D" (Drive)
  
  Transaxle starts in 1st gear and upshifts automatically to 2nd gear and then 3rd gear. Transaxle will downshift through all gears on deceleration.
• "2" (Second)
  
  Transaxle starts off and remains in 2nd gear for engine braking and better traction.
• "1" (First)
  
  Transaxle starts off and remains in 1st gear for engine braking.

When in "D4", 2nd, 3rd and 4th gears, torque converter lock-up exists and transaxle mainshaft rotates at same speed as engine crankshaft. Under certain conditions, torque converter lock-up clutch is applied during deceleration in 3rd and 4th gears. Torque converter lock-up is controlled by the PCM. The PCM receives various input signals and operates lock-up control solenoid valves. Operation of lock-up control solenoid valves controls the modulator pressure.

The PCM contains a self-diagnostic system, which stores a fault code if failure or problem exists in transaxle electronic control system. Fault code can be retrieved to determine transaxle problem area. For information on electronic transaxle components, see M5DA ELECTRONIC CONTROLS article.

Transaxle is equipped with shift and key interlock systems. Shift interlock system prevents shift lever from being moved from "P" position unless brake pedal is depressed and accelerator pedal is in idle position. In case of a malfunction, shift lever can be released by placing ignition key in release slot near shift lever. Key interlock system prevents ignition key from being removed from ignition switch unless shift lever is in "P" position. For additional information on shift and key interlock systems, see M5DA ELECTRONIC CONTROLS article.

The A/T gear position indicator on instrument panel contains lights to indicate which position A/T gear position switch on shift lever is in. For information and testing of A/T gear position indicator, see M5DA ELECTRONIC CONTROLS article.