Issues with hydraulics/gear box


Hello everyone,

It is my first post here, I just got the Audi A2 1.2 TDI a few months ago. I search the forum and I can't really find what I'm looking for. Don't crucify me please if I did not look hard enough.

from what I read on the forum, It seems I have a few issues with my hydraulics/ gearbox.

Problem one:
The car seems to shift at weird points. When downshifting the car goes in this very bad vibration mode just before shifting. feels like it's related to low RPM or something. when using the tiptronic mode the vibrations are gone. Feels like the car is gonna stall at each change on automatic mode. Also when i'm on Eco and i release the gas the car goes to neutral (rpm drop to around 800) and then bad vibrations again. this time it feel like a regular flocking... floc floc floc floc (like when you are crossing a bridge and rolling over those expenssions cracks). The clutch has been replaced 8 months ago by previous owner. Bad adjustments of some kind?

Problem two:
I did this test with the key on "ignition", foot on the brake, and counting the numbers of speed change on tiptronic mode before the pump start. I had two changes. From what i read it's pretty bad. So i changed the accumulator reservoir and now i got 3 changes. Wich is still pretty bad from my reading here. I guess i have a leak of hydraulic fluid somewhere. I looked around and it looks like there is fluid where the hoses are connecting. My plan is to replace the o-rings and retaining spring of the hydro hoses.

Qty:5 - Part Number: 085142420 - Description: O-ring
Qty:1 - Part Number: 6N0142425 - Description: Seal Ring
Qty:1 - Part Number: 085142110 - Description: Pin
Qty:1 - Part Number: 085142419 - Description: Retaining Spring

Good plan? Should the hoses be also replaced? Is there a link that explain how to do this? It seems not that complicated except for the very limited access space... does the system needs to be emptied of its fluids or a quick "zip zap zoop" is the way to go? Any bleeding necessary?

problem 3
Everybody is talking about the fact that the pump should start when you open the driver door. It doesn't on my car. My gas flap doesn't work also (switch is good). Could both problems be related to this micro switch that detect if the door is open?
found this video on youtube:
Is that really the way to replace that switch? anyone has a part number for this switch?

Ok, that's about it for this first post. Thank you very much in advance for your help. keep up the good work
ps: sorry for my limited english, bonjour aux amis francophones

I have no idea on points 1 & 2, but point 3 sounds likely to be the solder joints on the drivers door lock assembly.
The micro switches get blamed for a lot of issue that are actually the solder joints. You can take the lock assy out of the door, and strip it down. Check the micro switches with a multi metre and replace if needed. Re flow all of the solder joints ideally with some leader solder and flux, this fixed all of my door lock assemblies (and yes the fuel flap will not open if the car thinks the drivers door is still closed, suspect also the hydraulic pump will be on the same circuit)

Problem one - check the engine mounts. Does the engine vibrate with the car stationary and the engine running?

Problem two - unplug the hydraulic station and unscrew the accumulator half a turn. Pull out the spring on the gear actuator, and pull out the hoses,one at a time and replace the O-rings. Take care NOT to swap the hoses over. Replace with a new spring. Unscrew the single screw holding the plate to the base of the control station. Loosen the three (?) hydraulic station mounting bolts. Separate the plate from the station and replace the three O rings on the hoses. Replace the plate with the hoses (8Nm) and the mounting bolts (8Nm). Re-tighten accumulator and reconnect hydraulic station. You might find you still have only three changes due to internal wear of the gear actuator.

thanks RAB for the instructions, i will order everything this week and try this. Should i be worried about the gear actuator? Is it something that can be fixed?

There is some vibrations when the car is stationnary. I will try to look at the engine mounts.

I do you fill the hydraulic reservoir? Is it really this reservoir under the driver side headlight with the green cap? It look so unaccessible...
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I do you fill the hydraulic reservoir? Is it really this reservoir under the driver side headlight with the green cap? It look so unaccessible...

No, that's the power steering! Green cap on the hydraulic station. Disconnect the hydraulic station electrically and loosen the accumulator half a turn to de-pressurise system. Top up with VW steering oil so it is within the rectanglke on the reservoir. Re-tighten accumulator and re-connect station.

Ok! the vibrations when downshifting were almost gone after I changed the accumulator between 5-4, 4-3, 3,2. But it only last for 2 days... Now ****y vibrations are back... I still haven't change the O-ring but i hope this will help. It almost feel like the changes are slower than they should be. The "shifting up" was also smoother with less "dead time" between speeds. Why did the change of the accumulator made my problem much less for 2 days and then back to full problem... ? I don't get it... does bad basic settings could cause this kind of behavior? Or faulty actuator? but then why it had two good days? And why are the vibrations almost not there when using tiptronic mode...
In tiptronic mode the car is always in gear. That's the only difference. That might help to damp down any engine vibration. As suggested earlier, I would check your engine/gearbox mounts. I don't think that it has anything to do with your clutch/gear change mechanism.


You never fail to impress with your vast knowledge of all things 1.2Tdi and certainly more than live up to your 'Specialist' title.
Keep up the good work in 2017

Cheers Spike
Hi Spike,

Many thanks - you're too generous!

Hi Grimchuck,

It might be worth checking the three long bolts holding the engine mount to the block. These are stretch items that should be replaced every time the cambelt is replaced if you follow the work instructions to the letter. If they break, they might be difficult to extract. I only torque them up to the recommended figure without doing the stretch part; I've done this seven times now without any problems.

It might be worth posting a video of your engine at idle on here, if you can. It should be obvious then if you have a problem.

A simple method of evaluating engine mounts is to 'feel' the vibration on the engine side of the mount and compare this with the vibration on the chassis side.
If the mounts are in good condition they should stop most of the engine vibration reaching the chassis.
Just be careful with the fingers around hot or rotating engine parts

Cheers Spike
Thanks RAB and Spike,

I tried to check my engine mount but it's not easy when you have nothing to compare with. Spike, i'm gonna try your technic tomorrow. But it feels kind of loose to me. I can easily move the engine in the mount from side to side by hand without to much force. Also, i hear a knocking when vibration is bad (when downshifting) coming from the top (middle), front, right of the car. I think I will order this:

What do you guys think?
Looks pretty simple to replace.

RAB, for the bolts you are talking about number 13?

A big thank you for your help.

I tried your "feeling" technic

When i put my hand on the driver side frame rail and on the top of the fender, i feel much more vibration/knocking than on the passenger side.

Vibration/knocking on this side

Almost no vibration
I would say it's the engine mount (passenger side). You should not be able to move it like that, in fact I cannot move mine at all! The seven bolts to change the mount are all stretch items so all should be replaced. The mount bolts to body are 20Nm + 45deg and all the others are 40Nm + 90deg.