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 powertrain control module (PCM), sensors, and seven solenoid valves. Shifting and lock-up are electronically controlled for comfortable driving under all conditions.
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 A/T control system. The A/T control system includes shift control, clutch pressure control, and lock-up control. The PCM switches the shift solenoid valves and A/T clutch pressure control solenoid valves ON and OFF to control gear selection and torque converter clutch lock-up.
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.
The shift solenoid valves have two types:
- Shift solenoid valves A and D use ON-OPEN/OFF-CLOSE type; the shift solenoid valve opens the port of shift solenoid valve pressure while the shift solenoid valve is turned ON by the PCM, and closes the port when shift solenoid valve is OFF.
- Shift solenoid valves B and C use ON-CLOSE/OFF-OPEN type; the shift solenoid valve closes the port of shift solenoid valve pressure while the shift solenoid valve is turned ON by the PCM, and opens the port when shift solenoid valve is OFF.
The combination of driving signals to shift solenoid valves A, B, C, and D are shown in the table.
Electronic Control System (cont'd)
D position D3 Driving Mode Control
This automatic transmission is equipped with the D3 driving mode in D. The D position has two modes; general driving mode (shifts gears automatically 1st through 5th), and the D3 driving mode (shifts gears automatically 1st through 3rd). The transmission switches the mode when the D3 switch on the end of the shift lever knob is pressed with the transmission in D.
When the transmission is switched into the D3 driving mode, the D3 indicator next to the D indicator in the gauge assembly comes on. In the D3 driving mode, the D3 driving mode is cancelled by pressing the D3 switch, and the D3 indicator goes off. Also, the D3 driving mode is cancelled when the ignition switch is turned to LOCK (0). When the shift lever is moved out of D in the D3 driving mode, the D3 indicator goes off, but the transmission returns to the D3 driving mode when the shift lever is returned to D, and the D3 indicator comes on again.
Shift Control - Grade Logic Control
The grade logic control system has been adopted 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 engine coolant temperature sensor, the barometric pressure sensor, the brake pedal position switch signal, and the shift lever position signal.
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. The PCM does this 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 according to the magnitude of a gradient.
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 with different 4th gear driving areas, 3rd gear driving areas, 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 you are decelerating while applying the brakes on a steep hill, the transmission will downshift to a lower gear. When you accelerate, the transmission will then return to a higher gear.
Deceleration Control
When the vehicle goes around a corner and needs to decelerate first and then accelerate, the PCM sets the manual for deceleration control to reduce the number of times the transmission shifts. When the vehicle is decelerating from speeds above 25 mph (40 km/h), the PCM shifts the transmission from 4th to 3rd earlier than normal to cope with upcoming acceleration.
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, 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 will extend the engagement time of 3rd gear and 4th gear to prevent the transmission from frequently shifting between 3rd, 4th, and 5th gears. This allows the driver to have more control for both acceleration and deceleration.
The PCM monitors the average change in the vehicle speed and throttle over time. When these values exceed those for normal driving conditions, the upshift from 3rd to 4th gear and 4th to 5th gear is delayed. This gives more control over power, and the engine braking when the driver is driving aggressively around winding roads. The transmission will resume the normal upshift pattern after the PCM determines that normal driving has resumed.
Electronic Control System (cont'd)
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 lower and higher 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.
Lock-up Control
Shift solenoid valve D controls the hydraulic pressure to switch the lock-up shift valve ON and OFF. When the PCM actuates shift solenoid valve D and A/T clutch pressure control solenoid valve C ON, and lock-up starts. A/T clutch pressure control solenoid valve C regulates and applies 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 the D3 driving mode (2nd and 3rd gears).
Electronic Control System (cont'd)
PCM A/T Control System Electrical Connections
PCM A/T Control System Inputs and Outputs
PCM CONNECTOR A (49P) (square)
Electronic Control System (cont'd)
PCM A/T Control System Inputs and Outputs (cont'd)
PCM CONNECTOR B (49P) (triangle)
PCM CONNECTOR C (49P) (circle)
Electronic Control System (cont'd)
PCM A/T Control System Inputs and Outputs (cont'd)
PCM CONNECTOR C (49P) (circle)
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 Temporary DTC or a DTC. Depending on the failure, a 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 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 Temporary 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 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 them that allow the automatic transmission to continue driving. This causes a DTC to be stored and the D indicator to blink and/or the MIL to come on.