Function
Function
Controlling the shift solenoids when shifting
The solenoids are activated in a specific pattern to control shifting and the lock-up function. Solenoids S1 and S2 determine which gear is to be used at the time. Solenoids SL and STH determine engagement by adjusting the hydraulic line pressure of the transmission. The basic parameters for the different shifting points are the accelerator pedal (AP) position and the vehicle speed. The shift quality is decided by the control of torque and pressure control of the STH solenoid.
The pressurization of the clutches and the brakes are adjusted by reading the changes of the speed of the transmission input shaft during the shifting process and comparing them to the values calculated in the transmission control module (TCM).
Two shifting patterns can be selected, normal conditions and winter mode (selected using the button).
In normal mode shifting and lock-up occur at relatively low engine speeds to reduce fuel consumption. In the event of rapid accelerator pedal movements, the transmission control module (TCM) automatically shifts to sport mode.
Shifting patterns
Shifting program
Economy mode
When driving at normal acceleration, the transmission control module (TCM) uses a pre-set shifting program, optimized to shift for economy driving. This shifting program is suitable for "normal" driving which provides earlier up shifts and lock-up. In addition the transmission oil pressure is adjusted to provide smooth gear engagement.
Sport mode
In the sport mode shifting program the shifting points are adjusted to provide the best possible performance. Downshifts occur earlier. The transmission control module (TCM) selects the shifting and lock-up points which provide the best possible performance. The transmission switches from economy mode to sport mode in step 1 or step 2 if the accelerator pedal (AP) is pressed down quickly. The conditions are that the throttle opens and the vehicle speed exceeds 50 km/h. As soon as the accelerator pedal (AP) is released to a certain level economy mode is resumed.
Kick-down program
At wide open throttle (WOT) the kick-down function is engaged which provides quick downshifts for maximum performance. In this way a boost of power is achieved when overtaking for example.
Winter mode
Winter mode is selected using the (W) button on the top panel of the gear selector assembly. Winter mode enables starting off in a high gear to prevent the wheels from spinning on a slippery surface. This mode can also be used in other difficult situations in which the driver needs more direct control over gear selection. Lock-up can be engaged in 1st and 2nd gear. The shifting pattern is optimized to minimize the number of shifts. Depending on the gear position, the following combinations can be obtained:
- DThe car starts in 2nd gear. Automatic shifting between 2nd and 3rd gears occurs earlier than in Economy mode, D position
- 3The car starts in 2nd gear. 4th gear is locked out
- 2The car starts in 2nd gear. There is no up shifting or downshifting
- 1The car starts in 1st gear. There is no up shifting or downshifting.
The W lamp on the dashboard lights when winter mode is selected.
If kick-down is activated in Winter mode, the transmission uses all gears for maximum performance.
Other modes
Adaptation
The transmission control module (TCM) monitors each shift during all driving conditions to ensure consistent and smooth gear shifts. The control module does this by either lowering or increasing the hydraulic pressure used during the shift itself. The changed pressure levels are stored in the control module memory when the car has been switched off and are retrieved on start-up. This provides improved shifting comfort and increased service life.
Adaptation occurs when the following conditions have been met:
- Throttle opening is steady
- Oil temperature between 50 °C and 110 °C.
Temperature controlled lock-up
If the transmission temperature increases abnormally as a result of heavy load under high ambient temperature conditions, the torque converter lock-up function is activated as often as possible (temperature controlled lock-up). This reduces slippage and the generation of heat in the transmission. If the temperature is below +20 °C the lock-up function does not engage in order to increase the temperature of the oil more rapidly.
Shifting using Geartronic
When the gear selector is moved to the Geartronic position (MAN) the automatic transmission remains in hydraulic position D, but when the gear selector is moved upwards (+) the gear selector module (GSM) transmits a signal to the transmission control module (TCM) to shift up. When the gear selector is moved downwards (-) a signal is transmitted to the transmission control module (TCM) to shift down. The driver information module (DIM) switches the symbol in the combined instrument panel from D to the current gear, for example 3, when the gear selector is in the MAN position. A signal is sent to the gear selector module (GSM) to light the M LED and switches off the other LEDs. The transmission control module (TCM) determines if shifting can be carried out and the driver information module (DIM) indicates the current gear. If shifting is permitted the solenoids are activated according to each specific gear pattern.
However, in certain situations the transmission control module (TCM) assumes the shifting decision. The following applies:
- When stationary only 1st, 2nd and 3rd gears can be selected. 4th gear can be selected at speeds exceeding 30 km/h
- Automatic down shifting occurs for all gears below a certain speed. Example: 2nd gear is selected. Automatic down shifting occurs when shifting from 2nd gear to 1st at 2 km/h if the speed, before this has exceeded 25 km/h. in other cases 2nd gear is retained. For example, when 3rd gear is engaged despite the car being stationary
- Manual up shifting is required after automatic down shifting. Kick-down is not available in the Geartronic-position (MAN)
- The permitted speed for manual down shifting corresponds to those for kick-down up shifting, i.e. engine speed at approximately 6,000 rpm
- If the transmission temperature becomes too high the transmission control module (TCM) determines the shift position. The purpose is to maintain a gear where lock-up is possible at the current speed
- Lock-up is possible in 3rd and 4th gears. (1st and 2nd gears do not have lock-up).
Other
In the MAN position a signal about the lever position is generated for the gear selector module (GSM) as follows:
For each of the three gear selector positions a hall sensor is mounted on the printed circuit board for the gear selector control module (GSM). A permanent magnet on the lever affects the output signals from the sensors to the control module. The control module can read off the position of the lever through the differences in the signal characteristics.
Shift-lock
To avoid any chance of the gear selector inadvertently moving from the P position, the car is also equipped with an electrically operated shift-lock function. This locks the interlock pin in the gear selector lever in the shift-lock section, locking the selector lever in the P position. To move the gear selector from the P position, the ignition must be switched on and the brake pedal depressed. (The stop lamp switch is activated.). The central electronic module (CEM) reads the position of the brake pedal via direct connection to the brake pedal sensor and transmits a signal to the gear selector module (GSM) to deactivate the solenoid in the gear lever selector. The solenoid lock pin is pushed in and the gear selector lock button can be pressed down as usual to select another gear. When the ignition is in position "0", the solenoid is deactivated. In this position the gear selector is mechanically locked by the ignition switch interlock.
Ignition switch interlock
An interlock and security feature (ignition switch interlock) is mechanically connected to the ignition switch by a cable. The ignition switch interlock is controlled by the position of the lock cylinder in the ignition switch and by the position of the gear selector. This means that the gear selector must be in the P position for the ignition key to be removed from the ignition switch. The ignition key must be turned to position I or II before the lever can be moved from the P-position. The ignition switch interlock is used only in combination with shift-lock.
Park / neutral position (PNP) function
The gear-shift position sensor has a park / neutral position (PNP) function to prevent the engine being started with a gear selected.
This function prevents the engine being started unless the P or N positions are selected. This prevents the car from lurching forwards when started.
Adaptation data
There is a function for resetting adaptation in the transmission control module (TCM) which can be activated via VIDA vehicle communication. This must be carried out after replacing internal components, such as the valve housing or a solenoid, or when replacing the entire transmission.
Counter for transmission fluid data
A counter for transmission oil quality is built into the software for the transmission control module (TCM). The counter counts up the amount of time the oil is above a certain temperature. When the counter has reached the maximum value, the diagnostic trouble code (DTC) for an oil change is stored in the control module. When replacing transmission fluid, the counter must be reset to prevent a diagnostic trouble code (DTC) being stored incorrectly. This applies when the transmission fluid is changed and when the fluid is changed during a repair.
The reset function is activated via the VIDA vehicle communication socket.
Emergency mode in the event of a fault
If the transmission control module (TCM) detects a permanent fault, an emergency mode is activated. The transmission control module (TCM) then implements corrective action to protect the transmission, while leaving the car in the best possible drivable condition. Minor malfunctions do not activate an emergency program. There are different programs depending on the type of fault:
- Emergency mode
- Limp home mode.
Emergency mode is activated for minor faults and the Limp home mode for the most serious faults. If the malfunction is intermittent, the transmission control module (TCM) returns to normal operation the next time the ignition is switched on.
Emergency mode
A text message is displayed in the combined instrument panel for diagnostic trouble codes (DTCs) stored in the transmission control module (TCM).
The transmission shifts in all gears but transmits no signal to the lock-up solenoid. This means that lock-up is not available.
Limp home mode
A text message is displayed in the combined instrument panel for diagnostic trouble codes (DTCs) stored in the transmission control module (TCM).
The transmission control module (TCM) interrupts the activation of all solenoids. This means that no shifting is possible. The transmission only functions in 3rd gear and back-up (reverse) gear.
No regulation of line pressure solenoid STH. Maximum system pressure constantly which results in harsh meshing and harsher shifts when engaging P-R, N-R and N-D. This can also result in a whining noise from the transmission pump.