Auto transmission bad behaviour
 

My 75 is a facelift 1.8T auto. It's done 57k and has been well looked after.

I bought the car October last year and have found the behaviour of the transmission getting worse since. The symptoms:

• Occasional aggressive (thumpy) up-changes
• Very occasional reluctance to up-change
• OTT engine braking on downhill sections
• Not changing down/disengaging when coming to a halt (seems to change down through all gears in quick succession)
• Fighting against the gearbox drive when decelerating
• Thumping when shifting from Park in Reverse and into Drive.

The car was T4'd just after I got the car (on 47k) and was given a clean bill of health (all the solenoids were fine). I changed the gearbox fluid in the summer and noticed only a very mild improvement afterwards. Pulling the fuse or carrying out a battery disconnection reset temporarily improves things. Selecting 'Winter' mode improves matters considerably. These factors show the mechanical elements of the gearbox are not at fault and that it's an electrical issue.

The gearbox ECU is located next to the fuseboard behind the glovebox. To obtain the part number from the ECU (there are many different variants) I removed the ECU, disconnecting the multiplug. Once the PN was retrieved, it was reconnected and put back together. The test drive afterwards revealed a transformed car, with the transmission's behaviour improved considerably. Theory proved. Since that time, the ECU is relearning its bad behaviour and the symptoms above are returning.

So my question: as it seems my auto ECU is at fault, can they be swapped without being mated to the car? I have obtained another ECU removed from another 2004 1.8T but am reluctant to swap in case I cause some sort of network conflict in the car and render it undriveable. Any comments?

Did you notice any corrosion on the multi-plug pins?

If unplugging it helped then maybe it could be corrosion starting up again.:shrug:

A drop of WD 40 and a few more plugs and un-plugs might improve things.;)

Change the gearbox oil!

What grade of transmission fluid was used in the gear box.?

Already done - see above.

It was Carlube ATF-U.

Can't say I noticed any corrosion but then I didn't specifically check the pins. I'm going to unplug the ECU again this week so will check then. The area is bone dry.

Only asked as members Quote fluid recomended by JATCO is the norm,I have only ever used the recomended oil,and touch wood 150K OK,doing another change shortly,expensive to other oils,but only the best for the best. Tom.

Also carefully look at the wiring where it goes into the connectors, have come across more than one where although the wiring looks intact but upon closer examination the wire has fractured internally ;)

Russ

Interesting. I'll be sure to give it a closer look when I'm back under the glovebox.