After having some troubles with the ecu in my td5 d2 and attempting a replacement i discovered the action of the immobiliser.

Here are the things i found out about it in the process of getting the new ecu going again:


  • The ECU if in "robust mode" will only operate the engine if given the ok by the immobiliser.
  • The immobiliser is actually just a function of the BCU which is behind the dash.
  • When the immobiliser is deactivated, the BCU sends a unique digital signal along a dedicated wire between it and the ECU.
  • Surprisingly this is the only connection between the ECU & BCU, and the two computers operate independent of each other.
  • This signal/code must be learnt/paired to the ECU with landrover specific diagnostic tool. (eg hawkeye/nanocom/testbook)
  • Once this is done, it is this code that the ECU expects to receive, to decide if it can start or not.
  • This signal is surprisingly simple and low data rate (speed), operating at 250bps with the 'code' repeated continuously. The code it self has 2 halves, the second half is simply the 1st half inverted and repeated.
  • Theoretically it would be fairly easy to brute force (guess) the code as it is so short and there is likely no protection against this.
  • One could also capture and store their current BCU immobiliser code to then later transmit and use in the absence of a BCU capable or willing to do this.
  • The slow flashing red led on the dash, indicates active immobiliser.
  • I believe a programmable ECU (NNN) can have its immobiliser function disabled (non-robust mode).
  • The EKA (emergency key access) code can be entered via a unique pattern of drivers door lock turns, which temporarily 'disables' the immobiliser.
  • If the ECU has not learnt the BCU's immobiliser code, even using the EKA will not work as it is the BCU that the EKA operates on and 'tells' the BCU to transmit its code (disable immobiliser), which in the case the ECU does not recognise so will not start.
  • I personally had the situation where a 2nd hand replacement ECU learnt the BCU's code via nanocom, i was then able to drive. The next day it would not start, and it seems to have forgotten the code, and had to be re-learnt. It has not forgotten it since.