TIP: DQ400 - Functional limitation due to pressure drop (Lösung)

Hello everyone,

today I don't want to ask for help, but rather share my findings.

After having experienced this problem with the same vehicles, I dare to say that I have identified a pattern.

I'm omitting the details of the ordeal I went through the first time, which involved a long and costly journey to understand and fix the problem.

This applies to all hybrid vehicles from the Volkswagen Group with a hybrid drive and DQ400 six-speed transmission.

First, let's talk about the error pattern.

At some point between 180,000 and 250,000 km, error 30097 - Gear pressure P0867 begins to appear sporadically.

This results in a reduction in power, a speed limit of 3000 rpm, and error messages on the display for the gearbox and hybrid drive.

In the first few weeks, the error usually disappears after a restart.

If you ignore the problem for long enough or if there is a sudden drop in temperature, the fault will become permanent, and in the worst case, the vehicle will neither start nor be able to operate electrically.

VW offers either a new gearbox for €17,000 or, if they are willing, a new mechatronic unit including the control unit for approximately €6,000. In both cases, the fault will be permanently fixed.

However, in most cases, this is no longer a cost-effective repair due to the mileage of the vehicles.

If you try to fix it yourself, through independent workshops, or through specialized gearbox repair shops, you often suspect the pressure sensor of the primary high-pressure circuit. This is also evident in the fact that they sell like hotcakes. If, like me when I first had my car, you have the pressure sensor replaced, or like a friend of mine, you have the gearbox repaired with a new control unit, and the problem still persists, you are getting closer to the truth.

I'll keep it brief. The DQ400 has two gear oil filters. The large main filter is located at the top of the gearbox, and a smaller one is in the mechatronic unit.

The actual cause of the error message is that clutch wear has so clogged the small filter in the mechatronic unit that the pump can no longer draw enough volume to maintain the pressure.

This also happens even though, as with both of my vehicles, all service intervals have been adhered to, because (now), the main filter is NOT replaced during the DSG oil change [b]. It is only accessible when the engine and gearbox are removed, and it is only replaced if glitter or coolant is found in the DSG oil during the gearbox oil change.

So, if you happen to make a mistake, don't waste thousands of euros or dozens of hours, but instead order the Mechatronik internal filter for 16€ and take a whole day to replace it.

Ideally, you should also order a complete overhaul kit with all the seals and the intermediate plate from your preferred gearbox specialist, because then you really have everything in hand, and according to the manufacturer, all the seals must be replaced anyway.

I don't think I need to emphasize the importance of absolute cleanliness when working on the disassembled mechatronic. Please remember to flush the three small reverse valves in the distributor body first in the locking direction, then in the opening direction, using a suitable spray (not brake cleaner). This is where clutch dust often gets trapped.

Currently, I manage to complete the work in 7 hours, including basic setup and calibration run.

I hope you never find yourself needing this advice.

Best regards,

Bo

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I received a note indicating that the pressure sensor is actually the more likely cause than I initially suggested. Thank you for that.

Regarding this: does anyone know whether the error is usually electronic, or could the sensor also be affected by fine coupling dust and could it be cleaned through the opening with appropriate means?

Cool analysis that will surely help many.