It can be one of several things:-
1/ No power to the ECU, check black relay box near battery. Fuse contaminated, spade terminals contaminated to fuses or to relay/s. Any wiring contact in the box contaminated. (most likely answers - it stops power getting to the ECU). Check correct operation of the relays.
To be sure that everything is operating ok, check for +12v at the supply contact on the ECU.
2/ Yellow immobiliser faulty / intermittent (very rarely intermittent - can be permanently occasionally, so not the fault in this case).
3/ keys faulty - (never happens)
4/ faulty ring antenna - goes open circuit on rare occasions, but never intermittently.
5/ Immobiliser processor stuck in a loop, happens occasionally, just disconnect battery for an hour and try again.
You can see how it all points to the contamination in the black box.
Last edited by Barry; 25-10-13 at 19:29.