OK, well based on the last few posts, it sounds like a bad idea to let the locksmith near the borrowed ECU if there's a possibility he could alter or damage something by attempting to read the chip. Not going there!
I don't really want to consider this next option either, but... theoretically, would these ECUs all be identical, with the
only difference being the info stored on that EEPROM chip? If that's a yes, then would I be correct in thinking that, if the chip in the borrowed ECU was removed and installed in my ECU, and subsequently my truck started with the original ECU fitted and using the borrowed key matching that chip, then this would prove
beyond doubt that my ECU is OK, and the fault can only be in the programming of my original chip or the locksmith's inability to create a key that will communicate with it (most likely the latter)?
As stated, it's not really something I want to consider because it involves tampering with the working ECU, and the more I'm finding out about this system, the more I'm realising that a working, paired key and ECU is like gold dust. Something that is clear, however, is that buying the ECU available on
eBay probably doesn't get me any closer to a solution without the matching key for it. Other than, I suppose, it would provide me with a second bite of the cherry if I did decide to have a go at dis-assembling mine to attempt to re-program the chip.
I'm wondering about the possibility of buying the borrowed ECU from the owner and having the key copied so that it will physically start my truck, as sbman suggested earlier. Don't know if that's possible, but the off-roader from which I borrowed the parts is in a pretty sorry state and looks to have been sitting in the owners yard for many years untouched. He admitted to me that he's not sure if he'll ever do anything with it, so maybe it's a possibility?
sbman - please clarify something for me: if I let the locksmith have a go at copying the info from the working key onto a chip that can be inserted in the key he's already made that physically fits my truck, is there any way that the copying process can damage the original key? I'm hoping you can tell me no to that, in which case I might ask him to do that and try it - if that key then starts my truck, at least I then have a workable solution for now, even if it ends up being the case that I do have to give the borrowed ECU back. At least it buys me some time to investigate other solutions. Although, I have to say the idea of a new ECU & keys from Toyota at £400+ doesn't appeal! And I'll bet they're NLA anyway.