Some 2017-2018 Lincoln MKZ vehicles equipped with a 2.0L gas/electric engine may exhibit an illuminated MIL with DTC P013A in the PCM. This may be due to an exhaust system leak. Exhaust leak inspection should be conducted before performing a powertrain control/emissions diagnostics. Inspect the carbon soot/moisture witness marks at exhaust connections. Inspect welds at the CMS boss, flex pipe and flanges. Inspect catalyst monitor sensor (CMS) threads and crush washer to confirm that the sensor is fully seated in the pipe boss. Do not use a  Vacutec smoke machine to diagnose sensor leaks. Applying soapy water to exhaust connections including CMS threads while exhaust flow is restricted at the tailpipe and the exhaust system is pressurized at 5psi (do not exceed 5 psi) will increase ability to identify and confirm leaks.