A/T System Description - Electronic Control System

A/T System Description - Electronic Control System

Electronic Control System

Electronic Control

The electronic control system consists of the PCM, sensors, and eight solenoid valves.

Functional Diagram

The PCM receives input signals from the sensors, switches, and other control units, processes data, and outputs signals for the engine control system and the A/T control system. The A/T control system includes shift control, clutch pressure control, lock-up control, and A/T system hydraulic control. The PCM switches the shift solenoid valves and the A/T clutch pressure control solenoid valves ON and OFF in a specific sequence to control gear selection and torque converter clutch lock-up. It also controls the appropriate operating hydraulic pressure to the automatic transmission.

Shift Control

The PCM instantly determines which gear should be selected by various inputs from sensors and switches, and it actuates the solenoid valves to control gear selection.

Shift solenoid valve:
Shift solenoid valves A, B, and C switch to the hydraulic pressure supply circuit to the clutch. Shift solenoid valves A, B, and C are normally closed (ON-OPEN/OFF-CLOSE); the normally closed solenoid valve port opens to allow ATF to pass through when the PCM turns it ON, and the port closes, blocking fluid flow when turned OFF.

A/T clutch pressure control solenoid valve:
A/T clutch pressure control solenoid valves A, B, C, and D apply hydraulic pressure to each clutch via the hydraulic valve body circuit. A/T clutch pressure control solenoid valve D supplies hydraulic pressure to the torque converter clutch. A/T clutch pressure control solenoid valves A, B, C, and D are normally closed (ON-OPEN/OFF-CLOSE); the normally closed solenoid valve port opens to allow ATF to pass through when the PCM turns it ON, and the port closes, blocking fluid flow when turned OFF. These solenoid valves are controlled by current and are duty controlled depending on the vehicle speed and the throttle position.

Line pressure solenoid valve:
Line pressure solenoid valve A controls the hydraulic pressure in the hydraulic control system valve bodies of the automatic transmission. Line pressure solenoid valve A is normally closed (ON-OPEN/OFF-CLOSE); the normally closed solenoid valve port opens to allow ATF to pass through when the PCM turns it ON, and the port closes, blocking fluid flow when turned OFF.

The combination of driving signals to solenoid valves for each gear are in the following table.

Shift Control - Grade Logic Control

The grade logic control system is used to control shifting in D, and in S with automatic shift mode. The PCM compares actual driving conditions with programmed driving conditions, based on the input from the throttle position sensor, the engine coolant temperature sensor, the barometric pressure sensor, the brake pedal position switch signal, and the transmission range switch signal, to switch shifting control from the normal control to the ascending or descending control when the PCM determines that the vehicle is ascending a slope or being driven down a slope.

Grade Logic Control: Ascending Control

When the PCM determines that the vehicle is climbing a hill in D and in S with automatic shift mode, the system extends the engagement area of 1st gear, 2nd gear, 3rd gear, 4th gear, and 5th gear to prevent the transmission from frequently shifting between 1st and 2nd gears, between 2nd and 3rd gears, between 3rd and 4th gears, between 4th and 5th gears, and between 5th and 6th gears, so the vehicle can run smoothly and have more power when needed.

NOTE: Shift commands stored in the PCM between 1st and 2nd gears, between 2nd and 3rd gears, between 3rd and 4th gears, between 4th and 5th gears, and between 5th and 6th gears, enable the PCM to automatically select the most suitable gear based on the steepness of the grade.

Grade Logic Control: Descending Control

When the PCM determines that the vehicle is going down a hill in D, and in S with automatic shift mode, the upshift speed from 5th to 6th gear, from 4th to 5th gear, and from 3rd to 4th gear (when the throttle is closed) becomes higher than the set speed for flat road driving to extend the 5th gear, 4th gear, and 3rd gear driving areas. This, in combination with engine braking from the deceleration lock-up, achieves smooth driving when the vehicle is descending. There are descending modes with different 5th gear, 4th gear, and 3rd gear driving areas based on the steepness of the grade stored in the PCM. When the vehicle is in 6th, 5th, or 4th gear, and the vehicle is decelerating while applying the brakes on a steep hill, the transmission downshifts to a lower gear. When you accelerate, the transmission then returns to a higher gear from the current position.

Deceleration Control

When the vehicle goes around a corner and needs to decelerate first and then accelerate, the PCM goes into the deceleration control mode to reduce the number of times the transmission shifts. When the vehicle is decelerating from speeds above 27 mph (43 km/h), the PCM anticipates upcoming acceleration, and shifts the transmission from 4th to 3rd earlier than normal.

Shift-Hold Control

When negotiating winding roads, the throttle is suddenly released and the brakes are applied, as is the case when decelerating at the entrance of a corner, the shift-hold control keeps the transmission in its current (lower) gear as it negotiates the corner and accelerates out. When the vehicle is driven aggressively on a winding road, the PCM extends the engagement time of 3rd gear, 4th gear, and 5th gear to prevent the transmission from frequently shifting between 3rd, 4th, 5th, and 6th gears. This allows the driver to have more control for both acceleration and deceleration. The PCM monitors the average change in vehicle speed, throttle (accelerator pedal position), and differences in the rotational speed of all four wheels over time. When these values exceed those for normal driving conditions, the upshift from 3rd to 4th gear, 4th to 5th gear, and 5th to 6th gear is delayed. This gives more control over power, and engine braking when the driver is driving aggressively around winding roads. The transmission resumes the normal upshift pattern after the PCM determines that normal driving has resumed.

Shift Control - Manual Shift Mode

The transmission is equipped with a D-paddle shift mode in D, and with a sequential sportshift mode in S.
Either mode can be activated by pressing the paddle shifter + (upshift switch) or the paddle shifter - (downshift switch) while driving with the shift lever is in D and S.

D-Paddle Shift Mode

To engage the D-paddle shift mode, press either of the steering wheel mounted paddle shifters while driving in D. In this mode, the transmission can downshift by pressing the paddle shifter -, or upshift by pressing the paddle shifter +. Each time the transmission is shifted using the paddles, the shift indicator in the gauge control module displays the current gear. The display turns off when the transmission upshifts or downshifts automatically while coasting. The transmission stays in the current gear and does not upshift to the next higher gear if the paddle shifter + is pressed while driving below the minimum allowable speed, and the shift indicator blinks the number of the next higher gear several times, then returns to the number of the current gear.

S Position Automatic Shift Mode and Sequential Sportshift Mode

The S position has two shifting modes; the automatic shift mode and the sequential sportshift mode. In the S position automatic shift mode, the transmission upshifts and downshifts automatically from 1st through 5th gear, if the paddle shifters are not pressed. When the paddle shifter + (upshift switch) or the paddle shifter - (downshift switch) is pressed, the automatic shift mode is canceled and the sequential sportshift mode comes into operation. The shift indicator displays the number of the selected gear, and the M indicator come on. In the sequential sportshift mode, the driver can shift up and down manually from 1st through 6th gear by using the paddle shifters, much like a manual transmission. The paddle shifters are installed on the back of the steering wheel, and the driver can shift gears by pressing the paddle shifters without taking either hand off the steering wheel. In the sequential sportshift mode, the transmission must be shifted up and down by pressing the paddle shifters.
However, if the vehicle is coasting at a speed that would cause the engine to over-rev by downshifting, the transmission will not shift when the paddle shifter - is pressed. The shift indicator blinks the number of the selected gear position several times, then returns to the current gear. If the vehicle speed reaches an appropriate speed while the shift indicator is blinking, the transmission downshifts and the shift indicator displays the selected gear. Likewise, if the vehicle is driving below an appropriate speed to upshift when the paddle shifter + is pressed, the transmission will not shift. The shift indicator blinks the number of the selected gear several times, and then returns to the number of the current gear. If the vehicle speed reaches an appropriate upshift speed while the shift indicator is blinking, the transmission upshifts and the shift indicator displays the selected gear.
The sequential sportshift mode has automatic downshifting areas so the vehicle can run smoothly with more power to cope with upcoming acceleration. When coasting in 6th gear, 5th gear, or 4th gear, the transmission downshifts to the next lower gear if the vehicle slows down to the programmed speed, or by pressing the brake pedal. When the transmission decelerates to a stop, the transmission shifts to 1st gear automatically. The transmission can be shifted to 2nd gear by pressing the paddle shifter + while the vehicle is stopped, and the vehicle can start off in 2nd gear. The sequential sportshift mode is canceled when moving the shift lever to any position other than S.

Clutch Pressure Control

The PCM actuates A/T clutch pressure control solenoid valves A, B, C, and D to control the clutch pressure. When shifting between gears or during lock-up, the clutch pressure is regulated by A/T clutch pressure control solenoid valves A, B, C, and D to engages and disengages the clutch smoothly. The PCM receives input signals from the various sensors and switches, then processes the data, and outputs current to A/T clutch pressure control solenoid valves A, B, C, and D.

Lock-Up Control

Shift solenoid valve C and A/T clutch pressure control solenoid valve D control the hydraulic pressure to switch the lock-up shift valve and lock-up ON and OFF. When the PCM actuates shift solenoid valve C and A/T clutch pressure control solenoid valve D ON, lock-up starts. A/T clutch pressure control solenoid valve D applies and regulates hydraulic pressure to the lock-up control valve to control the amount of lock-up.

The lock-up mechanism operates in:

- D position - accelerating in 1st, 2nd, 3rd, 4th, 5th, and 6th gears.

- D position - decelerating in 2nd, 3rd, 4th, 5th and 6th gears.

- S position with automatic shift mode - accelerating in 1st, 2nd, 3rd, 4th and 5th gears.

- S position with automatic shift mode - decelerating in 2nd, 3rd, 4th, and 5th gears.

- S position with sequential sportshift mode - accelerating in 1st, 2nd, 3rd, 4th, 5th, and 6th gears.

- S position with sequential sportshift mode - decelerating in 2nd, 3rd, 4th, 5th, and 6th gears.

PCM A/T Control System Electrical Connections

PCM A/T Control System Inputs and Outputs at PCM connector A (square) (49P)

PCM A/T Control System Inputs and Outputs at PCM connector B (triangle) (49P)

PCM A/T Control System Inputs and Outputs at PCM connector C (circle) (49P)