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 seven solenoid valves.
Functional Diagram
The PCM receives input signals from 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, 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 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 actuates shift solenoid valves A, B, C, and D to control gear selection.
The shift solenoid valves are a normally closed type. When a shift solenoid valve is turned ON by the PCM, its port opens and the pressure from the shift solenoid valve(s) moves to the shift valves. When a shift solenoid valve is turned OFF by the PCM, its port closes, cutting off the pressure to the shift valves.
The combination of driving signals to shift solenoid valves A, B, C, and D and their respective gear position are shown in the table.
Shift Control - Grade Logic Control
The grade logic control system is used to control shifting in D. To control shifting while the vehicle is ascending or descending a slope, 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, and the shift lever position.
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 commands 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, from 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 engagement 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 with different 4th gear, 3rd gear, and 2nd gear driving areas according to the magnitude of a gradient stored in the PCM. When the vehicle is in 5th or 4th gear and the vehicle is decelerating while applying the brakes on a steep hill, the transmission will downshift to a lower gear. When the vehicle is accelerating, the transmission will 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, 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 A, lock up starts. A/T clutch pressure control solenoid valve A applies and regulates hydraulic pressure to the lock-up control valve to control the amount of the lock-up. The lock-up mechanism operates in D (1st, 2nd, 3rd, 4th, and 5th gears) and in D3 (1st, 2nd, and 3rd gears).
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 Pending or Confirmed DTCs. Depending on the failure, a Confirmed DTC is stored in either the first or the second drive cycle. When a Confirmed 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 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 report 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 it and substitutes a pre-programmed value for that signal to allow the automatic transmission to continue operating. This causes a Confirmed 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 do the test-driving diagnosis when the MIL is ON, or when the D indicator is blinking.
Electronic Control System (cont'd)
PCMA/T Control System Electrical Connections
PCMA/T Control System Inputs and Outputs at PCM Connector A (square) (44P)
Electronic Control System (cont'd)
PCMA/T Control System Inputs and Outputs at PCM Connector B (triangle) (44P)
Electronic Control System (cont'd)
PCMA/T Control System Inputs and Outputs at PCM Connector B (triangle) (44P)
Electronic Control System (cont'd)
PCMA/T Control System Inputs and Outputs at PCM Connector C (circle) (44P)
