A couple of observations Ollie:
So the BSIs cannot be reprogrammed once coded. But if you mean the confidential code for coding the keys, then you will need this to undertake that operation. Once the key transponders are matched and coded, they can't be re-coded to another BSI, but can be coded again to the same BSI. So I would start by getting the confidential codes of both your car and the donor car. Citroen will provide the code for a fee, on proof of car ownership, ID and address. As for the donor vehicle - if you have an invoice - or something to say it has been written off maybe....
So that is the first thing I would do - with the power cut to the BSIs, Engine ECU for extended periods, it is likely the transponders in the fobs need re-coding to their original BSIs again - but you will need the respective codes for each to do it.
Here is the sequence of what happens so you have a better understanding:
The following need to happen to unlock the engine ECU:
- The key with transponder must be identified
- The key with transponder must be authenticated
- The engine ECU and the BSI must be matched
This is the Key Identification Sequence
| Stage | Designation |
| 1 | The BSI sends an identification request to the switching module under the steering wheel |
| 2 | The switching module under the steering wheel transmits an electric signal to the transponder aerial |
| 3 | The aerial transmits the message to the key transponder |
| 4 | The key transponder answers by sending the key identification code |
| 5 | The key identification code is compared with the key identification codes memorised in the BSI |
| 6 | If the key identification code is memorised in the BSI. The BSI memorises the identifier of the active key. The key authentication session can begin
If the key identification code is not memorised in the BSI. The procedure is repeated every 100 ms for 2 minutes |
| Stage | Designation |
| 1 | The BSI sends an authentication request to the switching module under the steering wheel. The authentication request contains a random number and an encrypted password linked to the key identification code |
| 2 | The switching module under the steering wheel transmits an electric signal to the transponder aerial |
| 3 | The aerial transmits this message to the key transponder |
| 4 | The key transponder responds by sending the result of the authentication calculation. The authentication calculation is performed using an encrypting function and from the random number and the encrypted password |
| 5 | At the same time, the BSI performs a calculation using an encrypting function and from the random number and the encrypted password |
| 6 | The results calculated by the key and the BSI are compared |
| 7 | If the results are the same, the unlocking sequence continues
If the results are different, the BSI repeats an authentication request a maximum 2 times. The third time, the authentication request is deactivated for one minute |
The encrypting key is only determined in one way and is linked to the BSI code.
This is the Unlocking of the Engine ECU Sequence
| Stage | Designation |
| 1 | When the ignition is switched on, the engine ECU sends the BSI a random number |
| 2 | Using an encrypting function and from the random number and BSI code, the BSI calculates an authentication number |
| 3 | At the same time, the engine ECU also calculates an authentication number, using an encrypting function and from the random number and engine ECU code |
| 4 | If the key is authenticated, the BSI sends to the engine ECU the number used as a link authentication that it has calculated |
| 5 | The engine ECU compares the authentication number from the BSI with the one it has calculated |
| 6 | If the numbers are the same, the engine ECU is unlocked
If the numbers are different, the engine ECU remains locked |
The starting sequence is deactivated for one minute after 3 failed unlocking procedures.
- After the ignition is switched off, a 10 second timer is started.
- When the timing is ended, the engine ECU locks up.
- The engine cannot be started.
Display of the Engine Immobiliser Status
| Engine immobiliser status | Transponder LED status |
| ECU locked | Off |
| Ignition switched on | Lit |
| Recognizing the key and unlocking | Off |
| Key not recognised | Flashing at 2,5 Hertz |
| No connection with the engine ECU | Flashing at 2,5 Hertz |
| BSI and engine ECU not matched | Flashing at 2,5 Hertz |
The other point (not so much of an issue at present), is of course there are different options between the two cars - the replacement car:
No ESP *
Manual Seats *
Without Obstacle Detection *
No Sat Nav *
So the above will need to be changed if you haven't already done so later after you manage to get the car started of course
