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Jetta Hybrid DSG 7 dry. Mechatronic problem - DSG and S-tronic Transmission Forum -
Hi, I would like to share with you the problem I have suffered in my Jetta, and the solution I have apply, in case someone else may benefit of this.

Please, note I am not a professional mechanic, I just like it. When you do this kind of repairs you are assuming some risks, please, always secure your safety as the first priority, and keep in mind that you may generate a worse problem if you don?t have the correct knowledge. So please, be careful and have fun!

My car is a Jetta Hybrid Sport European version, but it is the same car as the one delivered in the Americas. (I think this is like SLI in the US).

The Problem: As soon as the car try to enter in electrical mode, by disconnect the petrol engine, it automatically switch on the petrol engine again. This sequence is repeated continuously.

The diagnostic output: If you run the diagnose test on your car, you would get a pressure problem in the hydraulic pump. Inside the automatic transmission (DSG7)

What is really happening?

- The mechatronic unit can not keep the pressure of the hydraulic fluid when the car enter in electric mode.

- This can be checked by displaying the values in the groups 30 and 31 in diagnostic software.

- The device which is activated when the engine goes to electric is the actuator for disengagement clutch (the K0). This is a piston which can be found on the top of the mechatronic unit. The valve block they call it. (The cable connected in the picture below was just to test the operation, it is 12 Vdc. You don need to do it)

Dealer solution:

- By VW protocol, any problem in the mechatronics area means, it will be substituted. No investigation at the local workshop. So, that means in Europe around 2500? problem

The solution I found after some investigation as you can imagine:

- I disassemble the valve block (you can do it directly, there is no need to remove nothing else from the car), and I found a 10 euro piston groove ring broken!!!

- After replace the part, everything works fine

In the picture below, you can see the piston, the broken groove is the one in the right of the picture

Below you can see the groove broken?.

Of course, you need to be extremely careful with some critical points:

1- Please, remember to remove the fuse for the hydraulic pump!!!: If you fail to do that, the pump will automatically start as you disassemble the valve block (Because the pressure drops below a certain level?) and imagine the mess you will create? Also, you need to be sure there is no pressure on the tank. But if you remove the pump fuse, and you start the car, the pressure will go to 0.

2- Very important after you complete the assembly, to bleed the hydraulic valve block and pipeline to the K0 attached. If you fail to do that, the car will not be able to operate K0 so will not enter in electric mode for quite a long time (can be days). Generating fail codes in the engine unit will appear. Not a big issue, but K0 could decrease life due to improper operation and according to your driving way.

a. You can bleed the K0 by executing a command in the diagnostic SW (quite risky if you don?t know what you are doing)

b. You can remove the big screw on top of the valve block and add some hydraulic fluid there. Not perfect but will help a lot.

3- Please, be sure you have 1 liter of hydraulic fluid, as you need to change all the fluid in the mechatronic unit. (one litter is the total unit required capacity 16?)

4- Purchase the FTE 28308L01 groove see below (10?)

Good luck and I hope this helps someone else? !!!!

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