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Discussion Starter #1
My car just brought up these two codes p0422/p0425 has anyone else had these come up?? P0422 is catalyst system below threshold. P0425 is a bad catalyst temperature sensor. Im lost and dunno where to start replacing parts. I have a high flow cat pipe that has 3000 kms on it and a brand new o2 sensor . Ne suggestions??
 

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system below threshold sounds like the computer doesn't think the catalyst is working adequately.

This is determined by the relationship between TWO O2 sensors - basically it wants to see a "cleaner" reading AFTER the cat than B4 it.... So it knows it's working....

Cat temp sensor I'm actually not familiar with, you might need to wait for someone familiar with a car that has that sensor on it.

HOWEVER, I could EASILY guess that if the sensor isn't reporting proper readings (bad sensor code) fixing that issue (sensor, wiring whatever the actual fault) would POSSIBLY solve the whole issue, and would be the place to start.

UNLESS this code came up immediately after the new O2 sensor was installed, pointing at that as the issue instead....

Luck!
 

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Discussion Starter #3
The O2 sensors i put in about 1000 kms ago. The light just came on last night . I cant see it being the cat. However, it seems to burn rich according to the ecu but pops like it is extremely lean. Someone else suggested the cat temp sensor is throwing off the computer that controls the fuel load put into it at diff temps. I think im gonna try some ford O2 sensors and see if it makes a difference. And find out where and how to replace this cat temp sensor.
 

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Your post mentioned ONE new O2 sensor, did you replace both?

AND, FWIW, MANY have had issues with aftermarket O2 sensors, especially the Bosch ones....

Bosch HAD a good rep., BUT their parts DON'T seem to work well on the Focus - O2 sensors & plugs have BOTH given posters here grief....

Mind you, I LOVE my Bosch Wiper Blades....

But in testing done by "Fanatics" on the Dyno, their plugs didn't perform well in the Focus, and there have been fitment & operational issues with the O2 sensors....

Luck!
 

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The ECU looks for a difference between the front and rear O2 sensors to determine whether or not the cat is working. The front O2 usually switches between 0 and .8 volts at a rapid rate as the ECU constantly adjusts the AFR for lean and rich conditions in closed loop. The rear O2 sensor (if the cat is working properly) will switch between a much narrower range of say .2 - .6 volts at a much slower rate. If you were to look at the two voltage wave forms on a scope at the same time the front form would be lots of steep up and down hills going from one voltage extreme to the other at a fast rate while the rear sensor would be some very shallow slow moving rolling hills.

Anyway. If it doesn't see this difference it will set this code saying OH GOD THE CAT IS BAD!!!(&^#($*&#$.

Now being that you have a high flow cat on the system (especially if its a cheaper one) it very well might be the cause for both codes. One side effect of a catalyst working properly is lots of heat out the other end. Most downstream O2 sensors nowadays have heaters in them to help get them up to operating temperature during cold startups and periods of idling where exhaust temps fall. If the ECU keeps having to turn the heater on in the O2 to get good readings chances are the cat isn't doing its job. And if the readings it keeps getting mirror that of the front O2 sensor, chances are its a bad cat. This theory is even more re-enforced by the fact that your sensors are brand new.
 

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Discussion Starter #6
I have a high flow cat mad eby dominic and the o2 sensors are bosch as well, Now after driving it i also got code p0420 which is also catalyst system below threshold on bank 1. And got code p0455 which is an evap leak. The car is burning extremely lean at idle and rich rich rich at anything after it . U can smell the fuel if your behind it. Im gonna get ford o2 sensors and a temp sensor and check all my evap lines and canister.

never rains but it pours.FML
 

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I see a lot of people that have problems with Bosch o2's. I have both Bosch o2's and mine is running fine. IMHO ford parts are just expensive.
 

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Honestly. I have a Bosch replacement O2 sensor on my Chevy S-10 with NO issues, just passed on the reports here that SOME have had issues when they were installed on Focuses, that went away when Stock units were used....


P.S. - The fitment was NOT like stock, and it'll probably be a PITA to replace when needed again, 'cause the nut did NOT have a "stand off" like the stock one to let you get a wrench on it (sits in a recess). So i WOULDN'T buy another...
 

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I always go with either stock or Denso O2's. Denso is all we use at work and have never had a problem. Makes a quality sensor.
 
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