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DSG7 Mechatronics

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Some garages and main dealers write-ff an entire DSG7 gearbox, when only the mechatronics unit is faulty. Rob Marshall partners with ACtronics, to discover how garages separate and reunite the two components safely, saving your customer money and ensuring a boost to your turnover and reputation.

Volkswagen Group’s Direct Shift Gearbox (DSG) is an automated manual twin- clutch design, introduced to offer a more efficient and faster-changing alternative to the traditional epicyclical geared/torque converter automatic types of transmission. The Audi TT 3.2-litre V6 was the first model sold in the UK to feature the technology. The 6-speed ‘wet clutch’ unit had its clutch packs lubricated by special oil that requires routine replacement.

The DSG7 was a development that not only featured an extra ratio but also offered reduced weight and higher efficiency. It debuted in 2008. A major difference was the use of dry clutch packs, located not within the gearbox casing but the bellhousing. For the sake of simplicity, this article focusses on the transverse 7-speed unit that the trade motor electronics remanufacturing specialist, ACtronics, reports as one of the most common units that its engineers encounter. We are not covering the longitudinal version, such as Audi’s S-tronic, although there are similarities.

HOW THE DSG7 WORKS

Like its 6-speed predecessor, the gearbox’s clutch and gear shift forks are controlled by a separate ‘mechatronics’ unit that is bolted to the side of the gearbox. It contains the Transmission Control Module (TCM – basically, the ECU) to control actuation of both clutch levers and the gear selectors. Unlike its wet-clutch 6-speed predecessor, the DSG7 contains its own oil supply, separate from that of the gearbox, and includes solenoid valves, slave cylinders, a pump and a high- pressure accumulator to maintain the required 40-60BAR.

The mechatronics TCM receives, transmits and reacts upon information that it receives not only from within the gearbox (such as internal shaft speed, gear position and oil temperature) but also externally from the car’s various other systems. Electrical solenoids that activate the hydraulic actuators then act upon a pair of clutch release levers and four gear shift selectors.

DSG7 PROBLEMS

Loss of drive is the chief complaint, due to an inability to select any gears. You may also notice flashing gear symbols displayed on the dashboard, which means diagnostic interrogation is needed to access a fault code. Should your equipment not communicate with the TCM, check the 30 Amps power supply fuse. Should a replacement blow instantly, the TCM has likely failed and retrieving a code is impossible. In any case, the mechatronics will require removal but, before you do so, perform your usual checks before jumping to a snap diagnosis, including verifying wiring loom condition, the battery’s state of health and alternator output.

Sulphur that is present within the gearbox oil manages to degrade the mechatronics body and penetrate the TCM, causing electrical shorts. Before a total loss of drive occurs, early symptoms include shuddering and even a loss of engine power. Yet, check that the many Volkswagen Group software updates have been applied. Other issues include the internal pump failing, causing a low-pressure situation and no drive – fluid leaks from the mechatronics breather (See Step 1) and a fault code relating to ‘Pump Play Protection’ tend to be the leading symptoms. Most main dealers would recommend replacing the entire gearbox and mechatronics unit together at a relatively huge cost. Thankfully, aftermarket garages have a cost-effective alternative to offer.

ACtronics reveals that, while separating the mechatronics from the gearbox is feasible for most technicians, repairing the unit requires additional expertise. Never attempt to strip the mechatronics on a workbench, because of the potentially lethal pressures contained within the internal accumulator especially, plus you risk damaging the delicate circuitry.

Aside from the cost implication, ACtronics advises that a remanufactured mechatronics unit is superior to even a brand-new part, because it contains the car’s original software. This means that no post-fitting software re-flash is necessary, although the system will require diagnostic recalibration afterwards.

HOW TO REMOVE THE MECHATRONICS

ACtronics advises that, before work starts, read all fault codes, set the gear selector lever to ‘P’, verify the radio code is present (if relevant) and set all of the gear shift mechanisms to ‘neutral’ diagnostically. The latter point is crucial, otherwise you will be unable to separate the mechatronics from the gearbox. You can do this via the VAG-com Diagnostic System (VCDS) under the Basic Settings Groups 61 and 62, for example. Should the TCM be damaged, you can do this manually; consult Step 5. Disconnect and remove the battery and its tray. It is also advisable to drain the gearbox oil beforehand (noting 30Nm for the drain plug) but do not forget to replenish it before restarting the engine post-repair.

Here is the complete transverse version of the DSG7; note the dry clutch pack within the bellhousing. We shall cover the replacement of these clutches in another issue of AT. The Mechatronics unit is identifiable by its black cover, which you must not remove. Prise off the oil breather cap (pictured inset) and seal the breather so that no oil can leak-out.
Disconnect the wiring plug that connects the mechatronics unit to the wiring loom. Other further operations may be necessary, such as removing the starter motor. Be very careful, as you prise the gearbox’s input speed sensor 3 (G641) from the gearbox, as pictured, because excessive force can cause the integral plastic locating tab to snap off, necessitating a replacement sensor.
3. This is the main special tool that you require (Part no T10407). It is needed to separate the two gearbox clutch levers (for the pair of dry twin clutches) from the mechatronics’ hydraulic slave cylinders. Consult also Steps 6 and 7.
4. The tool is inserted between the slave cylinders and the gearbox clutch levers – one is mounted behind the other one. The mounting lever’s groove must align with the strengthening rib on the gearbox casting, as pictured inset. Then, twist the lever clockwise 45 degrees – the position of the tool and its handle is what you should see after it has been turned. At this point, the tool locks into position. ACtronics advises that it must not be removed, until the mechatronics is reunited with the gearbox, because it might affect the clutch adjustment mechanism.
5. If you have been unable to select neutral diagnostically, it can be done manually at this point. Remove the gear selector bracket arm, which is clamped onto the shaft with a bolt. Then, remove the plastic cover by unscrewing its four attachment bolts. You can then access the relevant selector fork, which you can push aside to the left with a finger. Ensure, that you do not allow any contaminants to enter the gearbox. Clean the mounting surfaces, locate a new gasket and refit the cover and selector bracket, after consulting Step 14.
6. Seven T45 bolts hold the mechatronics in place, four of which are longer than the other three. Never remove the bolts that secure the black cover to the mechatronics body. Should you be working within a cramped engine bay, it is worth purchasing a pair of guide pins, pictured being held inset (part number T10406) that replace the two bottom bolts.
7. Be extremely careful, as you extract the Mechatronics unit from the gearbox. If you do not remove it in a straight line especially, you risk snapping the black plastic gear position sensors, which might necessitate stripping the gearbox to retrieve the broken parts.
8. With the mechatronics removed, you can access the four gear selectors easily – they have three positions. Ensure that they are all in their central locations. Mounted to each of the four selector forks is a plastic-coated magnet. Check that they are secure and not covered in swarf; otherwise you risk gear position sensor fault codes post-fitting. Consult the separate section on whether, or not, a DSG7 can be remanufactured, for more information.
9. Working on your remanufactured mechatronics unit, after checking it over visually, extend the four hydraulic actuators by 25mm and verify the measurements accurately with measuring calipers.
Every time the mechatronics unit is removed, the thick, rubber gasket that fixes to it
must be replaced. Check that both casting mounting surfaces are clean and that any tabs on the gasket that hold it into position are in the correct locations.
As you reunite the mechatronics onto the gearbox, mount the unit onto the guide
pins (See Step 6) and locate the collars on the hydraulic actuators (pictured in Step 9) within those of the four gear selectors, one of which is pictured. This ensures that the mechatronics can operate the gear selectors with no possibility of them becoming detached.
Once the mechatronics is in position, secure it with the bolts, but only finger tight. Remove the guide pins and refit the bottom bolts (pictured). Consult Step 13 before tightening the bolts crosswise to 10Nm.
13. Tool T10407 must still be in position. Before twisting 45 degrees counter clockwise and withdrawing it, ensure that the dimples on the two clutch slave cylinders align with the cups on the clutch operating levers. Misalignment can damage the mechatronics subsequently. Refit the speed sensor, as per Step 2.
14. Should you have to refill the unit with oil, note that the level cannot be checked. Therefore, it must be drained first, prior to being refilled with exactly 1.9 litres of Central Hydraulic Oil, but double-check the specifications in the car’s handbook. This can be added through the gear selector plate (see Step 5). Ensure that the breather (Step 1) is unblocked and intact. The mechatronics here is pictured separated from the gearbox.
15. While a remanufactured mechatronics unit retains the same software, it will still require reinitialisation after you have reassembled the car and checked the gearbox oil level. ACtronics reports that several diagnostic testers can perform the basic settings. As examples, VAS, ODIS and VCDS, all possess software with easy to follow steps.

ORGANISING MECHATRONICS REMANUFACTURING

ACtronics advises that you can check online, by logging onto www.actronics.co.uk and click on ‘free search’. Enter ‘DSG’ and follow the menus, prior to logging-in to complete the registration, which includes access to pricing information. Print off the Remanufacture Order Form afterwards.

As the Mechatronics unit can be damaged easily in transit, contact ACtronics’ Customer Service, which will send you suitable packaging. The unit must be packed so that no oil can leak-out, and enclose the Remanufacture Order Form, which is crucial for identification purposes.

CAN A DSG7 MECHATRONICS ALWAYS BE REMANUFACTURED?

ACtronics reports that remanufacturing is not possible in every case. Presuming that the mechatronics is not damaged physically, the specialist company advises that the presence of the following fault OBDII codes mean that the unit cannot be remanufactured. Yet, you might encounter these codes after fitting a remanufactured mechatronics unit, which tend to be caused by not mounting the shifters correctly within the gearbox forks (see Steps 11 to avoid this situation):

P072A – Neutral not selectable

P072B – Reverse gear not selectable

P072C – 1st gear not selectable

P072D – 2nd gear not selectable

P072E – 3rd gear not selectable

P072F – 4th gear not selectable

P073A – 5th gear not selectable

P073B – 6th gear not selectable

P073C – 7th gear not selectable

Should you extract the following position sensor codes, remanufacturing might be possible but more involved investigation is required. ACtronics advises checking the magnetic position sensors (such as those pictured) for metal particles, which may be caused by mechanical wear, or even damage, within the gearbox:

P173A – Position sensor 1 for gear selector, implausible signal

P173B – Position sensor 2 for gear selector, implausible signal

P173C – Position sensor 3 for gear selector, implausible signal

P173D – Position sensor 4 for gear selector, implausible signal

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