Hi.

Trying to figure out my sisters Ford Focus 1.8 TDCI 2004.

She left her lights on all day so came back to a flat battery.

Tried Jumping it but that didnt help- called the AA, who said it was a faulty immobiliser and towed it home.

The Key remote works fine, but the immobilser light flashes. The spare key (with the blue bit) doesnt work either..

A bita googling showed me how to "read" the light, and after about a minute if gives the code 15- which relates to the key, but I dont see both the keys being faulty.

What could be the problem?
Immobiliser? ECU?
Something else?

Thanks!