l want to thank everyone for all the help you all have given me,,,yu people ar EXCELLENT,,,,,hard to believe its been a couple of yrs all ready,,,,l have a PO420 catalyst system efficiency bank 1 below threshold,,what does this mean???? its from wifes ford focus, zetec 2. engine, 2001,,,could someone help me please....Thank you

 

Ford Focus Technical Chat - Focus Fanatics

 

As a general code, that normally means that A Your O2 sensor after the cat is toast (more likely) or B your cat is toast. I am not that familiar with the Focus so there might be another underlying condition causing the issue that is vehicle specific.

I would try using the link posted by 96 and posting there, they will be more familiar with the vehicle.

 

I am the cat guy so let me go at this

It means that your vehicle has been running poorly enough long enough to kill the converter. Your wife's Focus is a Low Emission Vehicle, and such vehicles are not tolerant of neglect. In all likelihood, the front O2 sensor is shot, the spark plugs probably need to be replaced, and the vehicle could probably use a good dose of fuel system cleaner.

As for the rear sensor behind that cat being the culprit, not very likely. There are some vehicles that will set P0420 codes when the downstream sensor goes, but no fords are among them. If you have a P0420 code, it has nothing to do with the signal strength of the rear sensor, it means that the cat is unable to store or use oxygen, as strong indicator that it is not working or damaged. Ford uses the waveform of the rear sensor to condemn the cat. If the cat is working, your rear waveform will be a steady signal of .4v or higher. On a bad cat, you get a waveform that mirrors the front O2 sensor signal. A bad rear O2 sensor will not mirror the front sensor.

By Ztec, I assume you mean the DOHC 2.0L witht he 8th digit of the vin being a 3.

If so, this should be the replacement converter you need, but you need to figure out why the original has failed first.

http://cgi.ebay.com/ebaymotors/Ford-...Q5fAccessories

 

thanks bear river,,she bought the car last winter and it has 188,000 klks on it, to pass e test they had to clean the egr valve and give it a tune up, l just changed the oil and filter and the vin# is1fafp34361w367761 its gonna take a while to sort out bugs,,it runs so nice and smooth,,when those codes came up the garage changed the downstream oxy and says the cat may be all right as there is a lot of power and the tailpipe is clean and dont smell,,if the codes keep on l will have em change the cat,,there is no codes now,,,,,thaks bear