FIRST pull the K.A.M. fuse for a minute or so see what happens.
Secondly I would be very surpirsed if a duff coil pack would flag a warning as the system has no way of knowing if the thing is working or not, ie wether sparks delivered it only knows that the electric was delvered to coil nothing else.
What is more likely particularly if twin HEGO is that it has flasshed a sensor malfunctuion due to unburnt fuel in exhaust and differential HEGO readings.

tabetha