96 Mercury Sable high idle and trouble code P0420

NSCHAFFER91

MEMBER
1996 MERCURY SABLE
120,000 MILES

Just bought the car and noticed it idles around 1300 rpms took it to autozone they hooked it up and saidit showed 2 codes one being high idle and the other being p0420 was told it could be oxygen senseror cadalac converter the car runs smooth no power loss is it possible the cat could be bad and not cause the car to die out cut out or loss of power? And what all could the problem be and how do I go about testing it?

3 Replies

FIXITMR

MECHANIC
9,990 POSTS

The computer in your vehicle uses an oxygen sensor in front of and behind each converter. The converter processes and reduces exhaust emissions. The computer program knows that there will be a difference in the information being reported from the front O2 sensor and the rear O2 sensor as the converter processes the exhaust emissions. As a converter ages it becomes less efficient. This loss of efficiency is known by the computer because of the information that the O2 sensors mounted before and after the converter report. Just because you have a converter efficiency code doesn’t always mean the converter needs to be replaced. A defective O2 sensor can cause this code to be set by the computer as well. Your technician has to check the O2 sensors to be sure that they are operating correctly and that other related systems are doing their job. If all checks good then a replacement converter is needed