Some 2017-2018 Ford Fusion 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 powertrain control/emissions diagnostics. Inspect for carbon soot/moisture witness marks at exhaust connections and welds, including catalyst monitor sensor (CMS) boss, flex pipe and flanges. Inspect the 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 while exhaust flow is restricted at the tailpipe and the exhaust system is pressurized at 5 psi will increase the ability to identify leaks.