Electronic Control System
ELECTRONIC CONTROL
The electronic control system consists of the Transmission Control Module (TCM), sensors, and six solenoid valves. Shifting and lock-up are electronically controlled for comfortable driving under all conditions. The TCM is located below the dashboard, under the front lower panel on the passenger's side.
SHIFT CONTROL
Shifting is related to engine torque through the A/T clutch pressure control solenoids, which are controlled by the TCM. The TCM instantly determines which gear should be selected, by various signals sent from sensors, and actuates the shift control solenoid valves A, B. and C to control shifting. Also, a sequential sportshift mode has been adopted to shift gears up and down manually in D4 position while using the shift lever. The combination of driving signals to shift control solenoid valves A, B. and C are shown in the table.
SEQUENTIAL SPORTSHIFT MODE
In D4 position while sliding the shift lever to the sequential sportshift mode position, the driver can use the shift lever to shift gears up and down, much like a manual transmission.
- Pushing the shift lever toward the "+" mark: Transmission upshifts to the next higher gear.
- Pulling the shift lever toward the "-" mark: Transmission downshifts.
The number of the selected gear is displayed in the shift indicator next to the D4 indicator. The transmission does not automatically upshift and downshift, and remains in the selected gear position (4th, 3rd 2nd and 1st). However, the transmission will automatically downshift as follows:
- Downshift from 4th gear to 3rd gear to get more power when climbing or to provide engine braking when going down a steep hill.
- Downshift to 1st gear when the vehicle comes to a stop.
To prevent engine over-revving, the transmission has 4-3, 3-2 and 2-1 downshift allowable speeds. When the vehicle is coasting over the 4-3 downshift allowable speed, 3-2 downshift allowable speed, and 2-1 downshift allowable speed, the TCM does not input the downshift signal from the shift switch, and the transmission does not downshift. When the vehicle is coasting over the 4-3 downshift allowable speed in 4th gear, and the 3-2 downshift allowable speed in 3rd gear, the TCM inputs the signal to wait until it reaches the downshift allowable speed, then the shift indicator blinks several times to indicate the lower gear position.
LOCK-UP CONTROL
The lock-up control solenoid valve controls modulator pressure to switch the lock-up shift valve and lock-up on and off. The TCM controls the lock-up control solenoid valve and the A/T clutch pressure control solenoid valves A and B. When the lock-up control solenoid valve is turned on, the condition of lock-up starts. The A/T clutch pressure control solenoid valves A and B regulate A/T clutch pressure control solenoid pressure, and apply pressure to the lock-up control valve and the lock-up timing valve; those of the lock-up control mechanism come into operation in 2nd, 3rd, and 4th gear in D4 and sequential sportshift mode, and in 2nd and 3rd gear in D3 positions.
GRADE LOGIC CONTROL SYSTEM
How it works: The TCM compares actual driving conditions with driving conditions memorized in the TCM, based on the input from the vehicle speed sensor, the throttle position sensor, the brake switch signal, and the shift lever position signal, to control shifting while the vehicle is ascending or descending a slope, or reducing speed.
ASCENDING CONTROL
When the TCM determines that the vehicle is climbing a hill in D4 position, the shift-up speed from 3rd to 4th gear becomes faster than the set speed for normal mode (flat road) driving to widen the 3rd gear driving area, so the vehicle can run smooth and have more power when needed. There are three ascending modes with different 3rd gear driving areas. The modes are based on information stored in the TCM.
DESCENDING CONTROL
When the TCM determines that the vehicle is going down a hill in D4 position, the shift-up speed from 3rd to 4th gear when the throttle is closed becomes faster than the set speed for normal mode (flat road) driving to widen the 3rd gear driving area. This, in combination with engine braking from the deceleration lock-up, achieves smooth driving when the vehicle is descending. There are two descending modes with different 3rd gear driving areas. The modes are based on information stored in the TCM. When the vehicle is in 4th gear, and you are decelerating on a gradual hill, or when you are applying the brakes on a steep hill, the transmission will downshift to 3rd gear. When you accelerate, the transmission will then return to 4th gear.
DECELERATION CONTROL
When the vehicle goes around a corner, and needs to decelerate first and then accelerate, the TCM sets the data for deceleration control to reduce the number of times the transmission shifts. When the vehicle is decelerating from speeds above 30 mph (48 km/h), the TCM shifts the transmission from 4th to 2nd earlier than normal to cope with upcoming acceleration.
ENGINE CONTROL IN COOPERATION WITH TCM
The TCM also sends signals of the following transmission conditions to the Engine Control Module (ECM) which controls the engine.
- When the transmission shifts gears, the TCM causes the ECM to control the engine ignition timing.
- When the transmission is in N position, the TCM causes the ECM to control engine rpm.
- When the transmission shifts into D4, D3, 2, 1 or R position at high rpm, the TCM causes the ECM to control the engine ignition timing.
- During a stall test, the TCM causes the ECM to control engine torque.