This is a 2008 Ford Fiesta that had been recovered to us as it would not start.
We initially noticed that the immobiliser light was illuminated and would not go off, but there was more to the story. Initially the car had a fault with the battery going flat due to the cooling fan continually running. The recovery company had attempted to jump start the car due to a flat battery but could not get it running.
First step was to get the car on the diagnostic machine to extract some more information from the vehicles ECU's. With this done we soon realised there was a fault with engine ECU being able to communicate with the immobiliser circuit. This instantly raised suspicions based on the fact that the immobiliser system is part of the engine ECU.
We attempted to re-program the keys to the car but although the keys would program the same fault was present. Now part of accurately diagnosing electrical faults with cars means that everything needs to be tested, and the most over looked part of fault finding by most is the vehicles wiring. We performed tests on all the wiring involved with the immobiliser system and found there to be no fault.
It had become apparent that the ECU had been spiked due to a surge in current when the recovery company had tried to jump start it. This is why we tell people continually that its not a good idea to jump start a car.
We fitted a new ECU to the vehicle and away it went. We then moved on to repair the fault with the fan and the customer was back on the road.