I'm not sure if the 315 is just the frequency of the remote rather than the transponder - I think it is, so I think that shoots a hole in my theory of the wrong type of blank key.

I could quit now, but where's the fun in that. I've ordered an RFID transponder reader to peek into the two keys I have and compare them with one from other source. I suspect that there are two ways to get a working key (besides paying for one through the dealer)

- find a way to get your VIN # added to the new key before pairing so it is accepted (that may well explain the 'challenge failed' message I was getting)

- clone an existing key using this kind of tool so the LR basically thinks it's seeing the same key each time. I don't think that needs any pairing then but I can't prove it. It may start the LR but not do remote lock/unlock.

It's a science project I admit but happy to share once I have some results!

If anybody reading this has an orphaned remote in their kitchen drawer for a LR they no longer own or even one where the remote batteries died and you never threw it away and you would feel disposed to donate it to science, please PM me....