Audi had quoted upwards of 6lac(8000$) to replace the gearbox. The first thing we did after purchasing it was to get the mechatronic unit out and fully disassembled:
We then proceeded to open the VFS solenoids followed by the others, here are some snaps for the curious:
Here’s an interesting paper on VFS solenoids: https://www.sae.org/publications/technical-papers/content/2011-01-0394/
The main culprit with this specific car was the clutch multiplexer solenoid. After fixing the solenoid and testing if it leaked the correct amount, we reassembled it.
Another issue was the wiring harness. It had a resistance of ~280k between the contacts of K1 multiplexer solenoid and VFS solenoid. We took an x-ray of the molded plastic wiring and there should have been no resistance at all between the two solenoids. Pathology lab was quite taken aback at the specimen which needed to be x-rayed! Here’s a shot of it:
Clearly there should have been no resistance and the plastic had started conducting over the years. Anyone with any ideas as to what could caused the plastic to conduct? High frequency PWM pulses are sent to the solenoids through this plastic, and it runs in 90-130 deg C temperatures of ATF(maybe the oil entered the plastic and started conducting? not sure)
So we proceeded to build a custom harness as even a replacement with new Audi harness would have failed after some time(was that their intention while designing?) and that’s unacceptable. We chose the most temperature resistant wires available and routed the wires away from all the high pressure oil outlets. The original black plastic molding is only to route the new wiring, it is not functional:
That is not where all the issues ended, even the ECU for the mechatronic had to be repaired(replacement is almost never a choice with us, we are focused on green solutions that generate minimal waste). It was not easy to repair. So much of the gel type epoxy with delicate wires. Static discharge was also something we had to keep a check on. Here’s a snap of the ECU from inside:
Audi/VW wasn’t really trying to make a reliable product I think! For shame, so many of these units are just thrown into landfills, not eco friendly at all. Doesn’t surprise me tbh *cough* dieselgate *cough*
Fully assembled and tested:
That’s all for now, next project would be a BMW auto I guess, let’s see!
Mechatronic failure? No big deal.
PS: Here’s the pinout of the gearbox connector on 0B5:
T16r- gearbox connector
T17q- red 17pin connector in plenum chamber
T17r- white 17pin connector in plenum chamber
2- T17q/10 -> T10k/3 -> J587
3- T17q/9 -> convenience control t32d/28
4- T17q/12 -> T4h/2 -> F305 gear selector solenoid
9- T17r/13-> CAN Low to ECU/(gateway T20d/16)
11- T17r/14 -> CAN High to ECU/(gateway T20d/6)
14- ST1/SB12 fuse
15- T17q/11 -> T10k/9 -> J587
16- ST1/SB1 fuse