Secondary Ignition Circuit

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 DTCs that can detect misfire and Ionization shorts in the secondary ignition circuit, refer to appropriate ENGINE ELECTRICAL DIAGNOSTICS article for more information