Understanding VW-Skoda DSG DQ200 failures in detail

The fragile design of the mech unit sets it up for easy failure.

BHPian Quadrant55 recently shared this with other enthusiasts:

Who is Srinivas?

Read my post about his FNG.

Background

Had recently visited German Motors to pick up my car and Srinivas was working on a DQ 200 mechatronics unit which was dismantled to the bone on his work bench.
So, I thought about picking his brain about its issues and what followed was a long Q&A session.
I later felt I should have probably recorded the complete conversation, it would have made writing this a whole lot easier. For now though, I have reproduced our conversation below to the best of my memory.

What follows below is not the exact order of the conversation. I have edited and rearranged some of it for tone and flow purposes.
Everything in bold is either my query to him or explanation to the reader. The rest is Srinivas’s voice

Issues

Why are there so many issues with the DQ200?
There are probably three main causes - Mechatronics, Clutch, TCU/M. Most times repeated failures are due to different parts failing one after another.
The major culprit is the mechatronics unit. To put this into numbers, off the 20 DQ200 cases we handled in the past few months (they are averaging 4-6 DQ200 cases per month and are unable serve at least another 2-3 due to lack of time and manpower) 14-16 were mechatronic failure. Of these barring 3-4 (which had an additional issue of clutch or TCU along with mechatronics), the rest had mechatronics as the only issue. That’s almost 80% of the failures.

Mechatronic unit with the back cover off


Other side of the Mechotronic unit with the TCU removed. You can clearly see the plugs which connect to the TCU. And with the accumulator removed

What’s the reason for the Mechatronic (mech) failures?
The fragile design of the mech unit sets it up for easy failure. Even in the mech unit, it is mainly the accumulator housing plate (its even called the valve body plate or accumulator body) that is causing the issue. The housing plate is made from aluminium and the walls of this housing (where the accumulator screws in) are quite slim and are unable to with stand the 60-70 bar pressure the accumulator generates. Over a period of time micro cracks occur and the accumulator fails to build enough pressure. This initially results in jerky or hard shifts. From there it just goes downhill.

Completely dismantled housing plate. Rear of the plate. Look at the intricate pattern for oil flow. This brittle wall is unable to withstand pressure

The dreaded - P17BF & P189C DTCs point to a clear case of crack in housing .The issue starts with micro cracks like this. But this whole area is now compromised, as time passes the crack only spreads

Does that mean the mechatronics has failed and the car won’t move?
Well, yes and no.

• Yes, the mechatronics has failed in the sense that once there is a crack, the housing plate it can’t be repaired. The crack/s can’t be plugged or welded etc. And even the accumulator gets damaged (it loses pressure) if there is crack in the plate. So even a small crack would mean both the housing and accumulator have to be replaced.
• No, the car will still drive and very few people will notice the jerks and hesitant shifting initially as it happens very sporadically. But as time passes the crack(s) only grows in size and the accumulator struggles to build enough pressure. In a bid to create the necessary pressure it starts to overwork, at which point the TCU activates pump protection protocol (anti-play protection), which is a measure to make sure the accumulator is not overworked and doesn’t overheat. This results in car being stuck and unable to change gear. This is a clear indication that the mechatronics is done. But even after this the car will drive. You just need to turn off the ignition and restart the car, it will drive normally for some distance (sometimes even few days or weeks can pass) before the issue reoccurs. Unfortunately, most owners don’t understand that this is just a limp/safety mode and continue to drive in this manner for months which exacerbates the issue.

In the initial stages it is just the accumulator and housing which will need replacing but as the issue aggravates the hydraulic pump and motor will fail due to overheating. And even before they fail sometimes some of the solenoids might give up etc. Overtime a bad mechatronic will affect clutch life too as inconsistent hydraulic pressure doesn’t allow the smooth and accurate engagement of the clutch. In extreme cases even the gear cogs get affected.

When you don't address it on time - aluminium will break off like a biscuit . This car's clutch also took the burnt of the neglect and had to be replaced

What about the other issues – Clutch?
I actually don’t see clutch replacements as an issue/defect. Clutches are normally wear items. And its very common for us to change the clutch even in manual cars. Most get their clutch plates replaced/overhauled between 60-100k mark. So, why is no one complaining of clutch issue with manuals?

In my view, (after the clutch lining improvement) the clutch life is mostly down to driving style and usage mix. I have recently replaced the clutch for a car(with DQ200) which did a little over 1,30,000 kms on its factory clutch. On the other hand, I have even seen some which failed at 35k kms. So, in my view this is a general wear issue, purely down to driving style and usage.

If that’s the case, why is clutch replacement considered a major issue with these gearboxes?
Due to the cost involved (compared to manuals DSGs clutches are quite expensive) and because its not the norm with other auto-boxes. DSGs have got a bad rep because they are probably unfairly compared to the other auto-boxes which usually don’t face this issue. But we need to make a clear distinction, DSG is unlike the other auto-boxes. It’s essentially a manual gearbox with 2 clutches controlled electronically. Or some might even say its two separate manual gearboxes and clutches with automated operation. The accumulator essentially takes over the function of your left foot.

So, when compared to torque converters & CVTs regular clutch replacement stands out as a red flag. With periodic maintenance other auto-boxes will do 3-400,000kms or more without any major parts needing replacement. But a majority of DSGs will struggle to touch 100k kms without a clutch replacement. Have you heard of same for the ZF 8 speed? Most probably not (after this he went into vivid detail about the design differences between Torque converters and DSG. About planetary gears, how the torque converter clutch discs are different, what ZF does differently to other torque converters et al. I have chosen not to reproduce that part here as I don’t recall the whole bit accurately and don’t want to misquote him. Will probably tackle this in a separate post later. Next time, will go prepared with a massive cup of coffee and notepad )

And TCU?
There are two main causes for TCU issues – heat and corrosion. Excessive heat is the enemy for any circuit board. The TCU is no different. Overtime this results in malfunctions or complete failure. Unpredictable gearbox behaviour (failure to engage certain gears, delayed or premature shifting) is a clear sign of a bad TCU.

The TCU connectors are another weak link, they corrode or fail due to overheating quite easily and this throws up multiple DTCs(Diagnostic Trouble Code). Most of the ‘short to ground’, ‘selector cannot be regulated’, ‘multiple gears engaged’ DTCs from the P170 series (172/3/4/6/7) are related to TCU miscommunication. A major cause of this is bad connectors.

TCU connectors corrode or fail due to overheating. The connector is part of the TCU frame. Multiple connectors which connect to the car and to the valve body/mech unit

Any other issues?
There are others like the gear selector issues – basically the gear selector fails and we won’t be able to engage that particular gear – like reverse or second gear. Sometimes bearings fail or the DMF (dual-mass flywheel) fails. But most of these are addendum issues. They happen because of abuse/misuse of another malfunctioning part. They generally don’t get triggered on their own.

Do these gearboxes under-perform once repaired? (I asked this because many members here had reported performance issues after repairs)
This is not that common. But will happen if the issue was misdiagnosed or repair job was botched. The measurements are very precise and tolerances are unforgiving. So, mistakes can happen. At times adaption might have been performed poorly.

What do you mean by misdiagnosed?
Diagnosing these issues is not as straight forward as we would like it to be. Most of the times during initial diagnosis/scanning, multiple DTCs show up. So, codes related to all three – mechatronics, clutch and TCU (or two of those parts) might show up. But usually, the actual cause might only be one of these parts. Like 60-70% of the time, the rest might be issues with two parts. Issues with more than two of these is generally rare. It only happens if the car is used for a very long time without addressing the preliminary issue. So, its quite easy to think that there is an issue with the mech unit instead of say the TCU or vice versa.

So, initial DTCs might have false positives?
Yes, most definitely. This is mainly true for multi-brand scanners like Launch or Autel. OEM diagnostic software (ODIS in this case) are better but even they throw up random codes at times. There are even times when no DTCs come up but the vehicle gets stuck in gear. This might happen in the beginning stages when the housing plate has just developed crack leading to temporary pressure loss. It might not even register as a DTC.

This crack never registered as a DTC. But the car was stuck in gear a couple of times.

Sometimes the DTCs might point to a problem. But the cause might not be evident right away. Once after scanning there was a pressure loss DTC(as shown in pic below). But we were unable to identify any cracks. In the end we were able to pin it down to a defective valve body which was contaminating the oil which in turn choked the filter. At the ASC the only solution for this is a complete mech unit change. Will probably cost 200k. Luckily, we were able to find a used valve body (not easy as in the used market they sell it along with the TCU which increases cost). And the customer saved probably 70-75% of his money.

Even a choked filter might lead to a pressure loss. The car might be stuck in gear or might just stall.


The filter and separator plates(these child parts are not easily available in India and are expensive) were also changed and issue was resolved.

How do you identify the actionable DTC?
That is ultimately down to the technician. A good long test drive will give us a better idea of the issue. We try to see if the issue can be replicated by us. With experience we would able to get it right around 95% of the time. But there will be times when we get curveballs where even our experience doesn’t help.

P177 series errors are notorious and the severity can range from minor to critical failure. Gauging the severity is crucial.

For instance, we had a car which had P177C – short to ground error. In our long test drive, we noticed some clunking noise. This a clear sign that the multi-clutch has gone bad, but the error never showed up even after multiple scans.

• And a ‘short to ground’ error in transmission electronics is related to the TCU. Nine out of ten times the solution for this error is to replace the TCU. But at times running the adaption settings might clear this error. So, every time we get this error we run the adaption first, test it for a couple of days and then if necessary change the TCU.

So, to get rid of the P177C we tried the adaption. When that didn’t work, we changed the TCU and the error was gone. Went for a couple of long test drives to see if the clunking noise would reoccur. It didn’t. So, we informed the customer that the clutch might be issue and delivered the vehicle. A month later the car came in again(was stuck in gear, no banging) and this time when we scanned it clearly showed clutch mechanical failure. So, we were not sure why it didn’t show that DTC before.

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