MIL on. Rough idle. DTCs are stored in the Engine Control Module (ECM), J623 (address word 01). Engine may have reduced performance without significant loss of power or stalling. Because there are a number of different misfire faults (unrelated to ignition coil operation) that could cause the MIL to illuminate, proper Guided Fault Finding (GFF) misfire diagnosis must be followed before any ignition coils are replaced.