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p420/430 code

J

jbloniak

Be Gentle I'm New Here
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Sep 4, 2008
Messages
1
I Have A V6 Ford Countor With 140,000 Miles And Its Throwing A 420/430 Code, I Have Changed Both Downstream Oxygen Sensors And Had The Pcm Reprogrammed, This Was Suppose To Widen The Threshole, But Soon As The Pcm Was Programmed The 430 Code Comes On Immeditly Once Its Clear, And The 420 Code Does Not Come On No More. I Used The Bc Cleaner And It Seemed To Help Out The 420 Code Bank 1, But Bank 2 (430) Still Keeps Coming On After The Code Is Clear.
The Car Runs Great And The Ford Dealer Says This Code Points To A Bad Converter, Does Anyone Have Any Ideas How To Handle This Problem Without Dumping A Large Amount Of Mony In This Car.
 
Ive had the same 2 codes for about 30k miles on both my cars. I just scan and clear every couple days. :laugh:
 
It usually doesn't help to change the lower sensors. It might help to change the upper sensors. Those codes are set when the cat monitor senses that the cat is inefficient. The cat monitor (in the PCM) determines the efficiency from the difference in the oxygen sensor switching rate. Prior to the cat, the sensor switches rapidly from rich to lean with the exhaust pulses. After the cat, the sensor should have very little switching. A lazy upstream sensor can cause those codes.

Another solution (although not really legal) is to install MIL eliminators on the downstream sensors, so the computer is fooled into thinking the cat is working by dampening the switching rate.

I would try the upstream sensors before trying anything else.

If you do a search, you should be able to find my postings on my experience with those codes. Although they would occasionally come up they would not repeat for several months. They have not returned since replacing both upstream sensors after the rear one died.

I forgot to mention that I have over 240,000 miles on the original cats and had no trouble passing a smog test about a month ago. The cats are working fine.
 
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I had a similar problem on my SVT not to long ago. i was not convinced that either CAT was bad as the car ran great. i changed the upper O2 sensors and that got rid of the P0430. while i was under the car about 2 weeks ago, i noticed the lower rear sensor wire harness was rubbing on the half shaft (polished a small section of the half shaft nicely :laugh:) i removed the sensor and found one of the wires was no longer insulated and thus grounding/shorting on the half shaft which would throw the code. replaced the sensor and made sure i secured the harness well away from the halfshaft. The code has not come back since (it used to come back every couple days)

I would start by replacing the upper sensors. with 140K miles on the car, they are likely well over due. if that doesnt fix the problem or only fixes one bank, swap the lower sensors from one bank to the other. if the code follows (P0430 becomes P0420) then the sensor is bad and needs to be replaced. if it doesnt then you likely do have a CAT problem.
 
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