From reading the Self-study on VW 09A transmissions (from the Russian site I linked above), I’ve put together this plan of attack for sussing out my problem. Please feel free to constructively critique – I don’t have a lot of mechanical knowledge – though am keen to learn. I also am thinking aloud in this post – so my train of thought may be a little disorganized.
I believe the most likely area of fault is with hydraulic oil pressure/temp. This is evidenced by the fact that the car works well once warm, but always suffers the problem initially – read whole thread for more info.
All Potential areas of fault I can think of from manual:
•ECU/TCU/engine torque sensor – In vehicles with Electric Accelerator Pedal Control (I have to find out if my car has this) engine torque data is sent to the TCU via the ECU. The TCU tells the ECU when it wants to change gears and the ECU lowers engine torque to allow the TCU to close clutches/breaks at lower pressure, making the gear change smoother – refer p.37. Therefore if there were any problem with the ECU, TCU or engine torque signal, this would manifest in less than optimal gear changes. However I think a fault in this area would be always evident (not only when cold) - agree?
•ATF temperature sensor (G93) – TCU uses ATF temperature data from this sensor to control gear changes. A high shift pressure is used at low ATF temperatures and varied as temp rises. If sensor fails, gearbox performs gearshifts at higher ATF pressures. This data is used at ATF temps. <70 degrees celcius – refer p.41-42. If this was playing up, it could be the culprit – but OBD should monitor this and VW dealer told me no VAG codes (will confirm – I just bought a VAG-COM).
•Solenoids – N88, 89 and 92 are used in 1st gear, but N92 is de-energized to go to 2nd. Possible this’s sticking? But not sure why that wouldn’t continue to be the case once pressure/temp is high – only thing I can think of is the viscosity of the ATF is higher when cold. Refer p.53. Again, could be the culprit – but OBD should monitor this and VW dealer told me no VAG codes (will confirm – I just bought a VAG-COM).
•Gear changes require individual brake/clutch operation (Clutch K2 and brake B2 must close for 2nd gear). There is also an accumulator on each brake/clutch, to dampen closure. If any of these failed, the gear change would be affected. (refer p.19 and 22, 24-25). But I think this would continue to be an issue when ATF warm, not just when cold - agree? Makes me think these are ok and the problem is hydraulic.
•ATF fluid itself – if chemically exhausted, or wrong level, it won’t work as reqd. VW dealer told me fluid level ok – I will confirm.
•ATF pump – this pump moves oil from the sump and transfers it to the v/v body. It is responsible for ATF pressure. Refer p.13. Is this monitored by OBD?
Most likely areas of fault that I can think of: ATF level/composition, ATF p/p. (This assumes my VAG-COM data confirms what the VW dealer told me about no OBD alarms – ATF temp. sensor ok, engine torque sensor ok, all solenoid v/v’s ok, etc).
Don’t know if all this stuff is replaceable if at fault – eg how hard is it to pull all of the transmission apart if say the fault is with the ATF pump? I just moved countries so don’t have many tools. I don’t mind buying cheap stuff, but won’t be buying crazy priced stuff. I also live in an Apt. complex which has no garage, so they aren’t real friendly with people doing work in the carpark – I have a couple friends with garages and tools though, so might be fine. Also got to work out logistics – only 1 car – how long will this be out of action for if I’m prodding transmission internals?
Plan of attack (in order):
1)check fluid level – if low, top up;
2)check reference resistances – if a problem, determine whether it’s wiring harness or solenoid;
3)check ECU/TCU/engine torque sensor – simple check?
4)ATF oil pump – Simple check?
5)ATF temp sensor – Simple check? Should be monitored by OBD.