Mechanics

OXYGEN SENSOR P0420 CODE

2000 Ford Focus

Engine Mechanical problem
2000 Ford Focus 4 cyl Two Wheel Drive Automatic 145000 miles

Have had this problem for a year car runs but now when I drive it is fine but when I stop or idle for short period of time it basically sounds like its going to die. So went to get the code read problem is I already changed it once before and check engine light came on 1 day after so what could cause the O2 sensor to go bad would I also need to change the catalyic coneverter this nvr happened until I got bad gas at a gas station 1 yr ago.
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Tlewis123
June 1, 2010.




This code indicates that the computer believes that your catalytic system is running inefficiently, i.E. You convert is getting old and clogged. This code can also be thrown by a faulty oxygen sensor. Because the car is running rough, I would estimate that one of your oxygen sensors are providing a false reading, causing the engine to correct for a fuel mixture that does not need to be corrected. This is likely causing you to run rich or lean, and it is most apparent at idle. My suggestion would be to replace your upstream oxygen sensor (closest to the engine) and clear the codes and see if that solves the problem. If not, replace the downstream one too. Oxygen sensors only last so long. Probably a good idea to replace both anyway.

Bill
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Tiny
Amraam35
Jun 1, 2010.
Yes, I agree, replace both o2 sensors (at same time) before you go paying big money for a new catalytic converter. But if you have been running the car like this for a year now, the false reading from the O2 sensor(s) would create the lean/rich mixture and would eventually cause the cat to go bad. This is why it is always a good idea to keep your O2 sensors as fresh as possible.

Tiny
Dshadowalex
Jun 21, 2010.

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