The Mechatronics of the Volkswagen Dual-Clutch Transmission
Many cars, mostly Volkswagens and Audis, have these unique advanced dual-clutch automatic transmissions. They have been around for a few years now and are hailed as an evolutionary step forward from the traditional transmission. People love them or hate them—it all depends on whether you had any problems with them. In 2009, VW recalled 53000 of them for defective mechatronic units.
The mechatronic unit is a computerized control part of the dual clutch system. It is complex and hard to troubleshoot when things go awry. When they do go bad, the dash will flash "PNDRS" and you will basically shut down wherever you are. You may be able to limp home in certain gears, or you may be stranded.
Volkswagen Dual-Clutch GearboxClick thumbnail to view full-size
The mechatronics are housed in the gearbox, surrounded by DSG oil. They make up the central control unit. All sensor signals and all signals from other control units come together at this point and all actions are initiated and monitored from here.
The unit has 12 sensors, By hydraulic means, it controls or regulates eight gear actuators via six pressure modulation valves and five selector valves, and it also controls the pressure and flow of cooling oil from both clutches. Temperatures of -40 °C to +150 °C and mechanical vibrations of up to 33 g occur and need to be dealt with. The oil temperature is kept from rising above 135 °C by an oil cooler. The gears are selected via selector forks in the same way as a manual gearbox. Each selector fork selects two gears. The forks are actuated hydraulically on the direct shift gearbox, not by selector rods.
Many times, the failures begin with sensor temps failing, either failing outright or falling out of specification. Many sensors have backups, so that if the main sensor fails a backup sensor will provide the data to the computer. If the data sent is incorrect, the computer will do what it thinks is right based on that incorrect data; hence, failures result. You may only be able to operate in certain gears or none at all. You may notice grinding or bad fuel economy.
Usually, if a sensor fails, only that section impacted by the sensor is effected. So, if a sensor fails for second gear, you will not be able to use that gear.
Sender G509, a key sensor, can be found in the housing of gearbox input speed sender G182. It measures the temperature of the DSG oil at the outlet of the multi-plate clutches. It operates in a temperature range of –55 °C to +180 °C. If G509 fails, the backup sensors may be able to prevent catastrophic loss. But if they fail, the tranny will go into self-protect mode and you will be stranded.
If your transmission suddenly starts to shift into odd gears or the car stops, it could be the N92 solenoid valve inside the mechatronics unit which controls activation of all the gears.
Components of the Mechatronic
Gear oil temperature sender
Gearbox input speed sender
Hydraulic pressure sender 1
Hydraulic pressure sender 2
Gearbox output speed sender 1
Gearbox output speed sender 2
Gear actuator travel sensor 1
Gear actuator travel sensor 2
Gear actuator travel sensor 3
Gear actuator travel sensor 4
Speed sender for input shaft 1
Speed sender for input shaft 2
Multi-plate clutch oil temperature sender
Control unit temperature sender
Engine control unit
Terminal 15 voltage supply relay
Onboard supply control unit
Steering column electronics control unit
Selector lever sensors control unit
Direct shift gearbox mechatronics
Solenoid valve 1
Solenoid valve 2
Solenoid valve 3
Solenoid valve 4
Solenoid valve 5
Selector lever lock solenoid
Pressure control valve 1 for automatic gearbox
Pressure control valve 2 for automatic gearbox
Pressure control valve 3 for automatic gearbox
Pressure control valve 4 for automatic gearbox
Pressure control valve 5 for automatic gearbox
Pressure control valve 6 for automatic gearbox.
On vehicle diagnosis, testing and information systems, use VAS 5051, the following modes of operation: Guided fault finding, Guided functions.
VW has made over 1 million DSG transmissions. Most are working fine with no problems, as long as the owner maintains them by changing the fluid every 40,000 miles and properly filling them to the correct level. Costs at garages range from $250-500. The DSG fluid runs $18 per liter, the filter $30. A new mechatronic unit is $4000-5000; a new tranny is far worse.