3.1 - Function Of Individual Components
1. Upshift and downshift switches
Installation position: in the steering wheel
In the manual shift gate, upshifting and downshifting can be initiated by actuating the tip switches. Manually actuated upshifting and downshifting are monitored by the Tiptronic control module and are not accepted if above or below limit speeds. Actuating the tip switch connects ground to the Tiptronic control module
2. DME control module
Installation position in Coupe: in the passenger compartment behind the emergency seat well on the right
Installation position in Cabrio: on the frame for the roll-over protection system in the convertible top compartment
The DME control module is connected to the Tiptronic control module. It transfers the following information through a data lead (CAN bus):
engine speed
engine torque
accelerator pedal position
engine temperature.
3. Tiptronic control module
Installation position in Coupe: in the passenger compartment behind the emergency seat well on the right.
Installation position in Cabrio: on the frame for the roll-over protection system in the convertible top compartment.
The Tiptronic control module is the information and command centre of the entire system. From a variety of incoming information (measurement values) which are compared with the driving and shift programmes stored, it selects the characteristic curve which suits the driving style and sends commands to the transmission to carry out or abandon shift operations.
If the Tiptronic control module is replaced, the following points must be observed:
1. Coding of country version
2. ABS/PSM version coding (G52 system)
Shift quality may worsen during the teaching phase of the transmission control system.
4. Coolant switch-over valve
Installation position: an the engine near the transport eyelet
Depending on the transmission oil and coolant temperature the switch-over valve is actuated by the Tiptronic control module. The valve sends vacuum to the flat-seat valve which in turn opens or closes the transmission coolant circuit. The coolant switch-over valve is open when it is de-energized. The coolant switch-over valve must be actuated in order to bleed the coolant circuit. 7.7.1 - Bleeding the Coolant Circuit
The figure shows the flat-seat valve in open position.
5. Multi-function switch
Installation position: on the transmission selector shaft
The multi-function switch has two tasks:
1. To supply the mechanical position of the transmission (P, R, N, D) to the electronic control module in the form of an electrical signal.
2. To prevent the engine being started in a driving position (R, D) and to allow it to be started in a standing position (P and N).
It is actuated directly from the selector lever by means of a cable.
It transfers the selector lever position to the transmission control module. It performs the switching operations of the reverse lights and is responsible for blocking the starter (by means of the DME control module) if a transmission range is engaged.
Coding of the positions is as follows:
6. Hydraulic control unit (switching device)
Installation position: in the oil sump of the transmission The hydraulic control unit contains electric actuators and sensors as well as a variety of hydraulic valves which carry out the gear change of the Tiptronic transmission in connection with the electronic control module.
The electric components such as:
solenoid valve 1, 2 and 3 (MV)
pressure regulator 1, 2, 3 and 4 (EDS) electronic pressure control
turbine speed sensor (rib speed - transmission) output shaft speed sensor (output shaft speed transmission)
are arranged so that they are accessible when the transmission is installed.
Short description of the valves:
Solenoid valve 1, 2, 3 (MV 1, 2, 3)
Installation position: on the hydraulic switching device in the transmission
There are three 3/2 solenoid valves, i.e. 3 connections and 2 switching positions in the hydraulic switching device. The solenoid valves are triggered by the electronic transmission control system and have two functions (open or closed). They are used to switch valves. (pressure range: 0 to 5 bar
nominal voltage: 12 V; pickup current: 166 mA)
Pressure regulator (EDS 1, 2, 3, 4)
Installation position: on the hydraulic switching device in the transmission.
The electronic pressure control valves convert an electric current into proportional, hydraulic pressure. They are triggered by the electronic transmission control module and actuate the valves belonging to the shift elements.
7. Sensor for transmission oil temperature
Installation position: The sensor is integrated into the wiring harness on the switching device side.
The sensor controls the modulation pressure of the transmission according to the transmission oil temperature. This means that gear shifts remain very comfortable over the entire temperature range
If the temperature of the transmission oil is too high, the control module selects a programme map with the smallest power loss possible and closes the torque converter lockup clutch. Also, downshifting occurs at higher engine speeds. This decreases the converter slip and the transmission oil can cool down.
The sensor is faulty if the prescribed signal voltage range is fallen below or exceeded. The shifting operations then occur with a substitute value of 80 °C
8. Sensor for transmission input speed
Installation position: on the hydraulic switching device in the transmission
The sensor (inductive pickup) transfers the transmission input speed to the transmission control system.
9. Sensor for transmission speed
Installation position: beside the hydraulic switching device in the transmission
The sensor (inductive pickup) transfers the transmission speed (output speed) to the transmission control system.
The control module calculates the speed from the transmission output speed
10. PSM control module
Installation position: in the front luggage compartment
The PSM control module is connected to the Tiptronic control module by means of a CAN bus. It transfers the following values:
- traction control (TC) active
- transverse acceleration
- reference vehicle speed
- longitudinal acceleration.
Because of this information, the Tiptronic control module goes into special programme maps.
11. Stop light switch
Installation position: in front of the brake pedal The Tiptronic control module requires the stop light switch signal in order to initiate downshifting before bends and to trigger the shift lock lift magnet.
12. Kick down switch
Installation position: in the accelerator pedal box in front of the accelerator pedal
NOTE: Since the accelerator pedal box may not be opened, the complete accelerator pedal box must be replaced in the case of a faulty kick down switch.
The kickdown switch detects depression of the accelerator pedal beyond the full throttle point. It connects ground to the Tiptronic control module, which displaces the shifting points for fast acceleration.
The transmission shifts down immediately depending on the speed, and does not switch back up until the engine reaches maximum speed. If the switch is faulty, kickdown is not carried out.
13. Selector lever with manual switch
The selector lever transfers the selector lever positions to the transmission and the multi-function switch by means of a cable.
In the manual shift gate, the manual switch connects ground to the Tiptronic control module, which in turn enables the manual tip switch.
Shiftlock (selector lever lock)
The function of the selector lever lock is to prevent the vehicle moving off unintentionally during manual shifting from position P or N (vehicle standing) to position R or D.
The selector lever lock is controlled by the transmission control system and is active in position P and N only. This forces the driver to actuate the brake pedal before selecting a driving range.
Function: The shift linkage of the selector lever is locked in positions P and N by an electromagnetic switch. The transmission control system is triggered and the locking button is released by actuating the stop light switch.
14. Instrument cluster
The selector lever position engaged and the respective engaged gear is displayed in the instrument cluster.
In the "reduced driving programme", the position display and the 4th gear blink in turn.
The instrument cluster is controlled by a serial wire from the Tiptronic control module.
The signal coding of the PWM signal is as follows: