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 the solenoid valves.

Functional Diagram

The PCM receives input signals from the sensors, switches, and other control units, processes data, and the outputs signals for the engine control system and the A/T control system. The A/T control system includes shift control, grade logic control, clutch pressure control, and lock-up 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 the torque converter clutch lock-up.






Electronic Control System (cont'd)

Shift Control

The PCM instantly determines which gear should be selected by various signals sent from sensors and switches, and it actuates shift solenoid valves A, B, C, and D to control gear selection.

There are two types of shift solenoid valves:

- Shift solenoid valves A and D are normally closed (ON-OPEN/OFF-CLOSE); the normally closed shift solenoid valve port opens to allow ATF to pass through when the PCM turns it ON, and the port closed, blocking fluid flow when turned OFF.
- Shift solenoid valves B and C are normally opened (ON-CLOSE/OFF-OPEN); the normally opened shift solenoid valve port closes, blocking ATF from passing through when the PCM turns it ON, and the port opens, allowing fluid flow when turned OFF.

The combination of driving signals to shift solenoid valves A, B, C, and D for each gear are in the following table.






Shift Control - Grade Logic Control

The grade logic control system has been adopted to control shifting in D. The PCM compares actual driving conditions with programmed driving conditions, based on the input from the accelerator pedal position sensor, the throttle position sensor, the engine coolant temperature sensor, the barometric pressure sensor, the brake pedal position switch signal, and the shift lever position signal, to improve shifting control while the vehicle is ascending or descending a slope.






Electronic Control System (cont'd)

Grade Logic Control: Ascending Control

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

NOTE: Shift programs stored in the PCM between 2nd and 3rd gears, between 3rd and 4th gears, and between 4th and 5th 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, the upshift speed from 4th to 5th gear, 3rd to 4th gear, and from 2nd to 3rd (when the throttle is closed) becomes higher than the set speed for flat road driving to extend the 4th gear, 3rd gear, and 2nd gear driving areas. This, in combination with engine braking from the deceleration lock-up, achieves smooth driving when the vehicle is descending. There are three descending modes stored in the PCM with different 4th gear driving areas, 3rd gear driving areas, and 2nd gear driving areas based on the steepness of the grade. When the vehicle is in 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 return to a higher gear.






Clutch Pressure Control

The PCM actuates A/T clutch pressure control solenoid valves A, B, and C to control the clutch pressure. When shifting between gears, the clutch pressure regulated by A/T clutch pressure control solenoid valves A, B, and C engages and disengages the clutch smoothly.

The PCM receives input signals from the various sensors and switches, then processes data, and outputs current to A/T clutch pressure control solenoid valves A, B, and C.






Electronic Control System (cont'd)

Lock-up Control

Shift solenoid valve D controls the hydraulic pressure to switch the lock-up shift valve and lock-up ON and OFF. When the PCM actuates shift solenoid valve D and A/T clutch pressure control solenoid valve C ON, lock-up starts. A/T clutch pressure control solenoid valve C 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 (2nd, 3rd, 4th, and 5th gears), and in D3 driving mode (2nd and 3rd gears).






PCM A/T Control System Electrical Connections





Electronic Control System (cont'd)

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)















Electronic Control System (cont'd)

Self-diagnosis

If the PCM detects the failure of a signal from a sensor, a switch, a solenoid valve, or from another control unit , it stores a Pending or Confirmed DTC. Depending on the failure, a Confirmed DTC is stored in either the first or the second drive cycle. When a DTC is stored, the PCM blinks the D indicator and/or turns on the malfunction indicator lamp (MIL) by a signal sent to the gauge control module via F-CAN.

- One Drive Cycle Detection Method:
When an abnormality occurs in the signal from a sensor, a switch, a solenoid valve, or from another control unit, the PCM stores a Pending and Confirmed DTC for the failure and blinks the D indicator and/or turns on the MIL immediately.
- Two Drive Cycle Detection Method:
When an abnormality occurs in the signal from a sensor, a switch, a solenoid valve, or from another control unit in the first drive cycle, the PCM stores a Pending DTC. The D indicator and the MIL do not turns on at this time. If the failure continues in the second drive cycle, the PCM stores a Confirmed DTC and blinks the D indicator and/or turns on the MIL.

Fail-safe Function

When an abnormality occurs in the signal from a sensor, a switch, a solenoid valve, or from another control unit, the PCM ignores that signal and substitutes a pre-programmed value for that signal to allow the automatic transmission to continue operating. This causes a DTC to be stored and the D indicator to blink and/or the MIL to come on. The transmission may not shift normally during fail-safe operation. Do not run the test-driving diagnosis when the MIL is ON, or the D indicator is blinking.