Mechatronics explained
Revealed: the box of tricks that governs a DSG gearbox.
Until relatively recently, the ‘traditional’ epicyclical-geared automatic gearbox with torque converter was hampered by its inefficiency, allowing it to fall increasingly out-of-step with the quest to decrease CO2 emissions that became linked with vehicle taxation policy from the early 2000s.
The result saw automated manual gearboxes being popularised. The types discussed in these pages are the twinclutch automated manual designs and, specifically, those fitted to Volkswagen Group models, which are the most common types in the marketplace.
New tech from old
Continuing development of the technologies established by the earlier Autoserve, Hot-shift and Porsche Doppelkupplung (PDK, or ‘double clutch’) gearboxes, the Volkswagen Group introduced its DQ250 6-speed DSG initially to markets outside Germany on its Audi TT 3.2-litre V6 model.
This transmission is referred to as a
‘wet clutch’ system, because its clutch packs are fitted within the gearbox and lubricated by a special oil. CM investigated the foibles of this particular unit in our February 2016 issue.
To enhance efficiency, reduce weight and lower emissions even further, Volkswagen Group introduced DSG7, a dry-clutch 7-speed DSG gearbox (code DQ200) across its Audi, Volkswagen, SEAT and Skoda brands from 2008. Instead of the clutch packs being installed within the gearbox, they are the more conventional dry-plated items, housed within the bellhousing. Yet, replacing the clutch assembly is a very different proposition to those fitted to a traditional manual gearbox. CM will examine this in a later issue.
The Mechatronics units are prone to failing on both DQ250 and DQ200 gearboxes, and may lead you to suspect a gearbox problem, when the issue is actually in the control unit. Its name stems from combining the terms ‘mechanics’ and ‘electronics’. The unit’s integral ECU receives information that relates to not only internal speed, gear position and temperature, but also parameters taken from the car’s other sensors – including those concerning the engine ECU, ABS, shift lever module and instrument cluster. This information is interpreted to control electrical solenoids that activate hydraulic actuators, through which pressurised fluid is pumped, to operate the clutches and gear shift selectors.
According to ECU Testing (located in Heanor, Derbyshire), issues with the later front-wheel-drive, transverse, DQ200 DSG7 Mechatronics units are
among its most popular repair lines and the company has become an expert in the component’s diagnostics, repair, coding and even remanufacturing. This version of the DSG7 is, therefore, our main focus. While DIY repairs are virtually impossible, due not only to the delicate electronics but also the potential safety issues, an effective way of saving money is to identify the signs of a failing Mechatronics unit and remove it from the gearbox at home, prior to mailing the unit to a specialist repairer for further analysis.
Diagnosing issues
The most common complaint is a complete loss of drive, due to the inability to select any gears. This is likely to be accompanied by warning lights being displayed on the dashboard, which might include flashing gear symbols. Check the main 30Amp fuse that provides power to the gearbox. Should you replace it and it blows again, it is extremely likely that the ECU’S Printed Circuit Board (PCB), located within the Mechatronics assembly, has failed. There is no DIY fix.
With a lack of power and/or a failed Mechatronics PCB, you may find that the gearbox will not communicate with your diagnostic scanner, making the access to fault codes impossible. Should you be fortunate and manage to retrieve the following codes: 16946/ P0562/001378 (System Voltage Low), 005636/P1604 (Internal Control Module), or P189C/006300 (Function restriction due to insufficient pressure build-up) and 10902/P17BF (Hydraulic pump play protection), suspect Mechatronics failure. Despite being known as problematic, however, do not jump to snap conclusions; make your usual pre-checks, including examining the condition of any wiring, to rule out the simplest issues first.
ECU Testing advises that a new main dealer replacement is not only very expensive (because the virgin ECU within the Mechatronics unit will require coding to your car) but it will also inherit an original design flaw – a software glitch for which ECU Testing has developed a solution. Yet, in most cases, ECU Testing can extract the coding from your original PCB and re-write it to the rebuilt unit, if necessary. This simplifies the post-replacement calibration, because the car will ‘recognise’ the replacement Mechatronics assembly as the one fitted originally.