SOLVED (see last post): Just putting this here in case anyone else needs it or can add anything.

Car was running fine. Park in usual spot overnight.
Next day, turn key, dash lights up normally, radio on, fan on, glow plug light turns off, turn key = nothing. No starter click, no crank, no nothing. Airbag pump silent.
Check battery. Indicated 12.33V. Disconnect and reconnect. No change.
Try various lock unlock combinations with key fob. No change. Alarm seems to be working fine.
Consult forum!
Read about possible XYZ switch. My gear lever (auto) is correctly displaying engaged gear light on selector AND on LED dash.
Bang on gear lever! Remove selector cover. Reinstall. Bang on gear lever again.
Retry ignition. SUCCESS!
This time.

I feel like I have dodged a bullet and I'm not really sure why the car restarted or if this problem will re-appear when I least want that to happen! Any clues here appreciated. If anyone else has a similar issue hopefully they will find this and it might help them!

 

I know on my P38 I’ve forgotten to put it in Park when shutting down, then when trying to restart it has the same symptoms so I think you’re on the right track with the gear position switch.

 

ONGOING: Car wouldn't start again today. Hasn't moved overnight since it started fine yesterday. Same symptoms. Left it there all day and used wife's car.
Retried later the same day, and managed to get it to start by shifting the gear lever randomly, but NOW I have the flashing green M+S and the red lights on the gear selector and on the LED are also flashing. Which is a NEW set of symptoms for me but this is the Limp mode I hear people talk about yes?

Where to from here?

Does this mean the XYZ switch is suspect?

 

Kia ora katou, e hoa.
Flashing M+S is limp mode -- sometimes it's caused by low battery charge. I would pull the terminals off the battery and clean them, then reconnect. I also highly recommend pulling the XYZ switch and opening it if it's a screwed type, spraying it full of CRC/WD40, working it backwards and forwards to clean the tracks inside it, then reinstalling and adjusting it so that the shifter works correctly.

 

Kia ora mollusc!

ONGOING/UPDATE:

Car not starting again this morning. retried key multiple times, Eventually something clicked and it fired up. No limp mode this time. moved it through the gears all appears fine. Off and on again. All good.
So after initial non start problem seems to have disappeared.

Checked battery. 12.5V. Reads 14.5V while running. Tells me the alternator is doing its job.
Checked ECU red pug for oil. Seems clean.
Cleaned battery terminals and put on charge overnight. Now reads 13.5V.
Test drive and move through all the gears.
Behaving and restarting just fine.

But of course this is exactly the kind of unpredictable unreliability no one wants from their daily driver…!

Anything else I should be looking at?

 

Iffy neutral switch would do it, which would explain it working once you run the gears. That is part of the XYZ switch.

 

Got another no start after car had been sitting unused for a few days. Tested battery voltage and back down to about 12.4V. I would think that would be enough but reading posts here it seems maybe at this kind of voltage things can get unreliable like this with the D2? Am thinking I might get the battery checked professionally and replace it if is getting tired. Also the battery in my key fob is old and weak so that might also cause issues right? I noticed if I remove the key and re-insert that sometimes clears it. So maybe that's not helpin either?

 

Battery in the fob shouldn't matter at all. You don't even need a fob -- everything will lock and unlock and the alarm system will fully disable with just a mechanical key. There's no RFID chip in the key either.

 

Still having this issue. Intermittently. Got my battery checked. It has 500CCA of its rated 800. So not the best but probably not the problem either. The spyglass is still showing green on the battery.

So I think it's time to look at other potential causes.

 

Have you checked for any pending codes in the system? Did you adjust the XYZ switch to be sure that it's correctly aligned?