Control System, Automatic Transmission

The AF20 (2.0L) and AF22 (2.3L and 2.5L) are four-speed electronically controlled automatic transmissions with a lock-up function of the torque converter on gears 3 and 4.

Transmission Control Module (TCM) 502
The transmission is controlled by a TCM (Transmission Control Module) which is supplied with digital and analogue signals from a number of sensors and from the engine's other systems.

The control module processes this information and calculates the optimum shifting points and lock-up engagement.

The control module then controls the transmission via control signals which act on the transmission's hydraulic system.

Optimum adaptation of the load to all driving conditions is achieved in this manner and shifting takes place with as little jerking as possible.

Compared with a conventional hydraulically controlled transmission, the AF20/22 transmissions offer the following advantages:
^ Improved shifting performance, smoother shifting due to torque reduction during the actual shifting process.
^ Fuel saving through consumption-optimized driving program.
^ Possibility of choosing different driving settings: Normal, Sport,Winter.
^ Self-diagnosis and storage of diagnostic trouble codes.
^ Less mechanical strain on the transmission.

Solenoid Valves 531
The various solenoid valves are located in the hydraulic system's valve housing under the valve cover on the transmission. These are controlled by the transmission control module.

Solenoids 1 And 2
Solenoids 1 and 2 are of the same design. They are both gear-shifting valves.

When current is supplied from pins 1 and 3 of the transmission control module, the solenoids receive a signal which opens or closes the oil circulation system in the shifting stages.

^ Solenoid 1: 1/2 and 3/4 shifting.
^ Solenoid 2: 2/3 shifting.

Lock-up Control Solenoid
The input signals received by the transmission control module determine when torque converter lockup is to be activated. When voltage is supplied from pin 19 of the transmission control module, a special solenoid valve is actuated and the torque converter clutch is locked.

System Pressure Solenoid
On shifting, the transmission control module acts on the transmission fluid pressure through a special solenoid valve.

This valve is controlled via pins 16 and 34 of the transmission control module.

Input Shaft Speed Sensor 532
The input shaft speed sensor transmits the speed of the input shaft to pin 12 of the control module.

Output Shaft Speed Sensor 533
The output shaft speed sensor transmits the speed of the output shaft to pin 30 of the control module.

Transmission fluid temperature sensor 535
The transmission fluid temperature sensor measures the temperature of the transmission fluid and transmits it to pin 33 of the control module.

Selector Lever Position Sensor 245
The selector lever position sensor is screwed to the gearcase and informs the control module of the gear that is selected

Normal/Sport Button 537
On starting, the transmission is in the Normal position but in positions D, 3, 2, lit is possible to select the "SPORT" position.
Normal = economical driving
Sport = sporty driving

The Sport position is selected by pressing the button on the selector lever knob. This causes the SPORT indicator lamp in the main instrument display panel to light up.

In the Sport position the transmission stays longer in the different gears.

The sport position will be disengaged if the sport button is pressed once again, if the ignition is switched on or off, if the "Winter" position is selected or if emergency operation is engaged.

Winter Button 506
To facilitate starting on slippery roads, the automatic transmission is equipped with a Winter position.

The winter button is to be pressed when in gear position D. When the transmission is in the Winter position, engagement of gears 1 and 2 is automatically prevented. The car starts in gear 3.

When the winter button is pressed the WINTER indicator lamp in the main instrument display panel lights up.

The Winter position will be disengaged if the winter button is pressed once again, if the ignition is switched on or off, if speed exceeds about 80 km/h or if emergency operation is engaged.

Brake Light Switch 29
Depressing the brake pedal actuates the brake light switch which sends a signal to pin 26 of the trans mission control module. Under certain conditions this causes the transmission to shift down and the lockup function to disengage during braking.

Cars With TCS
If wheelspin occurs, the TCS control module sends a signal to pin 4 of the transmission control module to indicate that Traction Control is in operation.

The transmission control module uses the TCS throttle position on pin 15 to determine torque limitation when changing gear.

Kick-Down
Up to a certain speed range, the Kick-Down function permits brisker acceleration of the car.

This function is obtained when the accelerator is fully depressed past the wide open throttle position. Located under the accelerator is a Kick-Down switch which closes when the accelerator pedal touches it.

This causes a signal to be sent to pin 8 of the control module and, depending on whether the speed of the car is sufficiently low, downshifting immediately takes place and engine performance is utilized to the full without heed to fuel consumption.

Shifting up to the next highest gear takes place at maximum engine revs.

Engine Management System
The engine management system provides the transmission control module with information on:
^ the throttle position, pin 25. The transmission control module provides the engine management system with information on:
^ torque reduction, pin 13, for smoother shifting. The engine management system then adjusts the ignition timing angle.

Lamps In The Main Instrument Display Panel
In the case of certain faults in the Transmission Control Module (TCM) system, a signal goes from pin 6 of the transmission control module to the main instrument display panel which lights up the CHECK GEARBOX warning lamp at the same time as one or more diagnostic trouble codes are generated.

When the sport button is pressed, a signal goes from pin 24 of the transmission control module to the main instrument display panel which lights up the SPORT indicator lamp.

hen the winter button is pressed, a signal goes from pin 7 of the transmission control module to the main instrument display panel which lights up the WINTER indicator lamp.

SHIFT LOCK Function
A SHIFT LOCK function is provided on cars for certain markets. The selector lever is mechanically locked in the P position on starting.

Depressing the brake pedal releases the mechanical detent and the selector lever can then be operated in the usual manner.