P0420 code ford taurus?

In the Ford Taurus, P0420 is often caused by a bad oxygen sensor, but there can be other causes as well. The code technically stands for: CatalySTSystem Efficiency Below Threshold.Your Taurus has at least two oxygen sensors, one before and after the catalytic converter. Among the many jobs that oxygen sensors have is they have to measure the emissions levels coming in and out of the converter. When the readings from the upstream and downstream oxygen sensors show similar readings, the vehicle will throw the service engine soon light (P0420). Typically, the code will be triggered by the upstream oxygen sensor (before the converter).There arent usually any drivability issues associated with P0420. For most people, the firSTSign that anything is wrong at all is the service engine soon light coming on.