Overhaul - Mp7A: Operation

Shift lever has 7 positions. When shift lever is moved, manual valve on main valve body is moved by the shift cable. When certain transaxle gear combinations are engaged by clutches, power is transmitted from the mainshaft to the countershaft through the sub-shaft shaft to provide different gears. Shift lever positions operate as follows:

• "P" (Park)
  
  Front wheels locked 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 selector engages with countershaft reverse gear and 4th gear clutch is applied. Backup 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/4th)
  
  Transaxle starts in 1st gear and upshifts automatically to 2nd, 3rd and 4th gears. Transaxle will downshift through 3rd, 2nd and 1st gears until vehicle stops. When in 2nd, 3rd or 4th gear in "D4" position, TCM sends signal to operate torque converter lock-up.
• "D" (Drive/3rd)
  
  Transaxle starts off in 1st gear and upshifts automatically to 2nd gear and 3rd gear. On deceleration, transaxle will downshift through 2nd gear to 1st gear. When in 3rd gear in "D" position, TCM sends signal to operate torque converter lock-up.
• "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 "D" position in 3rd gear or "D4" position in 2nd, 3rd or 4th gear, torque converter lock-up exists and transaxle mainshaft rotates at the same speed as engine crankshaft. Under certain conditions, torque converter lock-up clutch is applied during deceleration when in 3rd and 4th gears. Torque converter lock-up is controlled by the TCM. The TCM receives various input signals and operates lock-up control solenoid valves. Operation of lock-up control solenoid valves controls the modulator pressure.

The TCM contains a grade logic control system which controls transaxle shifting while vehicle is ascending or descending on a slope or reducing vehicle speed. For more information on grade logic control system, see MP7A ELECTRONIC CONTROLS article.

The TCM contains self-diagnostic system, which stores Diagnostic Trouble Code (DTC) if failure or problem exists in transaxle electronic control system. The DTC code can be retrieved to determine transaxle problem area. For information on electronic transaxle components, see the MP7A ELECTRONIC CONTROLS article.

The MP7A transaxle is equipped with a shift and a key shift interlock systems. The 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 about the interlock systems, refer to the MP7A 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 the MP7A ELECTRONIC CONTROLS article.