I was just getting a few old fobs I have accumulated over the years ready to send off to have their codes read.
The plan being to input a known fob code into the HSK's Becm and see if I can get a working fob for it.....
Going through the fob bin, I found I had an extra fob for Bolt making 3......The one in the bin said it was key 1.
This got me thinking I could test my theory before sending a parcel to the UK......
I have read somewhere that you can only change the first code number (not correct) so, I went into Bolt's (unlocked) Becm and read the 3 stored codes. The first one happened to be 64, so I went to the HSK to input that into it's (also Unlocked) Becm. I found that the first number in the HSKs Becm was already 64......Caused me to recall I had tried this about 2 years ago without success.....
However, being a bit tenacious about this sort of thing, and seeing as I had no working fob for the HSK, I went ahead and loaded all 3 codes from Bolt into the HSK....What could possibly go wrong??
In this case, nothing went wrong, and the Becm accepted all 3 codes. Figuring one had to be correct, I tried to sync the fob.....
I pulled the key from the non working fob that came with the HSK and inserted it into the now working fob.
As this is the Missus' daily driver, I am now a hero in her books!
I am going to send the other 2 fobs off to be read as they work, but I have no way of getting the codes for them.
This means, of course that if you have a fob on the correct band, a Nano or equivalent, an unlocked Becm, and a way to get the fob code, you can very easily make any fob work! Even the ones that they sell on sleezebay!!
Now for a large celebratory Rum!
Just a little bit of info for you on how this actually works....
You cannot input 3 fob codes into the BECM. The FOB code section is actually 3 bytes of data, as a hardware ID transmitted by the fob to the vehicle. The fob code you program into a BECM is the 3-byte ID of Key #1 of a lockset. The BECM then will accept this code and the following 3 ID's. This is how they get a 'lockset' of 4 fobs, and how they can program a new one from the factory, as there will be a record of the lockset barcode (which must have the ID 1 encoded in it somehow) and then say you want key 2 - then you can know what the lockset ID1 is, and then work out from that what the ID of 2/3/4 should be and program a fob to that ID, so that it would sync to the BECM.
The fob reader that I have will read the ID that the specific key is transmitting, and work out whether it's a Key 1/2/3/4 and tell me that. I can then work out (in the case that it's not a key 1) what the key 1 code would be, and this is what would get programmed into the BECM.
So if you have programmed your other BECM with the same codes, then they will both listen to the same fob codes (so you could in theory sync fob 1 to one vehicle and fob 3 to the other vehicle. but if you someone synced the remote from one vehicle to the other, it would operate it (on the fob at least) which could put the rolling code out on the other vehicle and de-sync it from there.
If you have other working fobs, then I would still probably get one of them read (especially if you have 2 from another vehicle/lockset) as then you could write the fob 1 code from the other lockset to the other vehicle and then have 2 working fobs for both vehicles... or at least 1 for one vehicle and 2 for the other. Or if you have multiple fobs, then read all of them, so if you need to replace one at some point then you have the codes needed for the rest.
In theory, I could get any key from any vehicle, read the fob code, work out what the #1 code from the lockset is and program it to any BECM - BUT you CANNOT take 2 keys from DIFFERENT locksets and get them programmed and have the BOTH work on the SAME BECM. you could program the fob code from one OR the other lockset, not both.
Regarding unlocked BECMs... I have read that there CAN be issues with unlocked BECMs, but I haven't been able to find out what they are either. The only thing I have read for sure is that you could get problems with communicating with the HEVAC if the BECM is unlocked. And that the fix for it is to unplug the connector to the BECM that has the diagnostic wires in it. I haven't however had the issues myself (my BECM is unlocked, and never have trouble talking to the HEVAC - not any worse than any other P38).... so I'm wondering if it was an issue on earlier ones that got fixed in later revision BECMs/firmware versions.