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, increases the oxygen content in the exhaust, deceiving the PCM in to thinking the fuel system is too lean. Also see MISFIRE MONITOR  . There are DTC's that can detect misfire and Ionization shorts in the secondary ignition circuit, refer to the Powertrain Diagnostic information