Secondary Ignition Circuit
WARNING: This page is about a different car, the 2007 Chrysler PT Cruiser. However, it is still accessible from the selected car via links, so may be relevant.
The PCM cannot detect an inoperative ignition coil, fouled or worn spark plugs, ignition cross firing or open spark plug cables. The misfire will however, increase the oxygen content in the exhaust, deceiving the PCM in to thinking the fuel system is too lean. Also see misfire detection. There are DTC's that can detect misfire and Ionization shorts in the secondary ignition circuit, refer to the appropriate Engine ELECTRICAL DIAGNOSTICS article for more information