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Discussion Starter #1
THis problems has been annoyed me for years, and now that inspection has come around I can't pass any of the tests. Especially considering that every time I reset the codes, I have to complete a drive cycle in order for it to be ready for inspection.

P0133
O2 Sensor
CKT Slow Response
(Bank 1 Sensor 1)

P0420
Catalyst Efficiency
Below Threshold
(Bank 1)

Those are codes, I have already replaced the front o2 sensor but it really didn't fix the problem, cel popped up less than a 1000 miles after It was fixed. I have a RT high Flow cat and Focus Sport SCT tune. You guys have any solutions? I dont really want to spend the money for another o2 sensor.
 

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what kind of sensor did you purchase? if it was a Bosch sensor then that is prob your problem. I've had 3 go in one month! Motocraft is what i bought next and works great.
 

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Discussion Starter #3
Yea, it was a Bosch, but would a malfunctioning fron 02 sensor cause both of the ob2 codes?
 

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3,263 Posts
i didn't get the second code but i got slow response from both sensors cuz of the bosch sensors
 

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Bank 1 Sensor 2 would be the sensor that would cause a cat efficiency code because its main job is to monitor the converter.
 

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I AM DA FOCI FANATIC
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3,715 Posts
The rear sensor causes the cat low efficiency

The front 02 is your slow response
 

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The Librarian
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13,116 Posts
Moved to "Ford Focus Technical Chat".

When it comes to the O2 sensors on the SVTF, it's best to stick with Motorcraft.
Get a hold of Mike Trendel (b16sir1991 on FF) at Hilbish Motors.
He is a vendor on this site, and has his own forums:
http://www.focusfanatics.com/forum/forumdisplay.php?f=94
NOTE!
Calling him will get much quicker results than posting a thread or sending him a PM.
^^^He can get you a lot better price than you'd pay locally.
 

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You've got a basic engine operating/performance issue here, particularly considering your mods. That cat efficiency code is very often caused by a lean mixture (cats can only handle so much O2). Does your MAF reside in the original spec. housing or is it in an aftermarket housing that has a different inside diameter or profile? Any vacuum leaks, fuel delivery issues?
 
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