Where is the 02 sensor code P0420 bank 1 in a '99 Mercury Cougar V6?

Answer 1

Answer
catalytic converter efficiency below threshold.
http://www.v8sho.com/SHO/TSB0197HO2SServiceTips.htm see web site for sensors locations, copy and paste website in address.....
A code PO420, catalytic converter efficiency below threshold, is more likely an indication of a catalytic converter problem, not the sensor. There are different codes that would indicate a sensor problem. However, it is possible that a sensor problem may be the cause of the catalytic converter code appearing. The sensors (newer cars have two or more) measure the differences between exhaust gas before and after the converter(s). Faulty sensors could indicate a faulty converter when it might be the sensors' bad measurements that are the cause. However, a faulty sensor should also generate a bad sensor code. Sometimes another indicator of a bad catalytic converter might be a vibration in the exhaust system near the converter caused by pressure in the converter or a breakdown of the honeycomb material inside the converter.