Excellent research. +++ I think that's consistent with what I worked out and documented in post #16 above. ;) Z1 = 1100, Z2 = 1010.
There should be another code for between D and 4/S. And a 4th code for 4-3 and 3-2 if have that available.

So we do now know that those intermediate positions exist and are recognised by the TCU, though not if it does anything (or what) as a result.
This could be the basis of another useful diagnostics test on the F125, moving the shifter slowly and monitoring the TCU.
Where exactly in VCDS do you find those codes?

I couldn't get it to show anything for that - it just went straight from one to the other.

Its in measuring blocks. I can't remember which one but not very far in. Scroll through and you'll see it.

Automatic Transmission (2), Measuring Block 4 and it also shows the binary 4-bit codes on the F125, exactly as I had worked out in fact. ;)
There's a higher block (11?) that shows some of that data (and Tiptronic IIRC) but block 4 is best. :cool:

My car is of course exactly the same, only Z1 and Z2, no code between D and S.

BUT a really interesting observation! When VCDS was showing Z1 or Z2 the DIS was no longer highlighting a selector position.
It was still showing PRNDS but no red highlight until the stick moved slightly and the F125 showed a standard position.
MJ, is this what yours was doing when you struggled to get reverse or was PRNDS missing?

Edit, I think you did have PRNDS displayed, so that could indeed have been a Z1 or Z2, not a totally invalid code, just "in transit":
And in fact my initial guess may well have been correct, with a Z1 code being read:

Yep thats exactly it. It must have been seeing Z1, so not throwing any errors. Only in that one specific position did it get R.

I wonder what Craigs TCU was seeing when he had his gearbox problems, maybe also Z1?
Bearing in mind it was his problem/question that caused this thread to be initiated. ;)

Good to see he's got it going now, but I did struggle to understand what the initial problem was. It looked like it was something really serious but I think it was just that "P" wasn't illuminating on the DIS (though everything may have actually been working) which was down to a shifter cable adjustment. :Confused:

This highlights a couple of things, firstly that the two sides of the F125 really are electrically/electronically independent and work very differently and secondly that mechanical devices can work incorrectly but be sending valid signals (at the wrong time) so often no errors are logged by the IT kit.

Just to throw in an update to this thread after studying the insides of an F125 a bit more. And my recent problems described in this thread: https://forum.a8parts.co.uk/showthread.php?t=17345
I now think that the (narrow) code between D and S/4 is definitely 1111.

As with Z1 (1100) and Z2 (1010) this code (1111) removes the highlighting and VCDS shows it as gear stick position Z3.

I don't have a PRND432 shifter to test but it looks like the 4-3 code is 0011 and 3-2 is also 0011.
So we have Z3 for code 1111 in addition to Z1 and Z2 so maybe 0011 will be called Z4?

I can confirm that today, while testing my F125 I did indeed briefly (and more than once) see Z4 as the gear in VCDS with 0011 as the code.

So we have recognisable interim codes of Z1 (1100) Z2 (1010) Z3 (1111) and Z4 (0011) displayed by VCDS. What the TCU does about them who knows, but it does definitely remove any highlighting on the DIS when they are detected.

But either the TCU or engine ECU do something!
Today, as noted elsewhere, my F125 was flickering between N (1110) and Z3 (1111) while stationary in Neutral with the engine running. Every time it switched to Z3 the revs increased to over 1000 and dropped immediately it went back to N.

As I was parked on level ground I released both footbrake and handbrake for a while during this. There was no movement so I think the gearbox stayed firmly in neutral but the engine was definitely preparing for something, presumably assuming it was between D and 4?