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Old 10-29-2008, 09:23 AM   #1
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Exclamation Check Engine Light. P0420 Code

Hello everyone,

I recently bought a 2001 Ford Focus ZX3 3 days ago . The check engine .

engine light came on and I took the car to Autozone which they told me that

computer code which was P0420.

I googled the code and it kinda told me that it had to do with the 02 sensors

or the Catalyc converter not working properly.

I was wondering if anyone has received this code before and how did they

resolve the issue??

Thanks for all your help in Advance...

John


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Old 10-29-2008, 11:57 AM   #2
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It sounds like your cat is dying or, more likely, the downstream O2 sensor is bad.

Check this out to understand better what the code means:

http://www.aa1car.com/library/p0420_dtc.htm

I myself would just replace the downstream O2 sensor and see if the code goes away.


P.S. How many miles on the vehicle? Mileage is often a useful bit of info in diagnosing things.
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Old 10-29-2008, 12:03 PM   #3
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Thanks for helping me out Penguin,

The current milage on my car is 72,380 miles..

I was thinking of replacing the O2 sensors, but honestly I was going to start with the

top one.

So if the 02 does not work then go ahead and change the cat??

Thanks in advace for all the help..

I am new to the Focus so I am just having fun..

Great forum..
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Old 10-29-2008, 12:13 PM   #4
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> I was going to start with the top one.

It is the one after the cat that monitors the cat performance, and which I think would be the most likely culprit.

But here's some more info to digest:

http://www.obd-codes.com/p0420

http://www.tegger.com/hondafaq/p0420.html

http://www.alldatadiy.com/techtips/T...20060131c.html


Good luck!


P.S. I believe the cat has an 80,000 mile warranty, but since you bought it used, it might not be covered, e.g., if somehow the prior owner(s) got some leaded gasoline into the vehicle, or if it was run a long-time with a prior misfire, or some other abuse., it would not be covered.
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Old 10-29-2008, 02:19 PM   #5
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Thank you so much Penguin for the excellent advice.

I will replace the upper O2 sensor first on the car this comming weekend. If that does

not take care of the problem I will replace the Cat.

Since the cat is going to be very expensive then I will just ride with the yellow light for a

while if the 02 sensor is not the culprit.

Also I read all of the links very interesting.

Thanks again.
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Old 10-29-2008, 11:16 PM   #6
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I just fixed a P0420 last week.. It was the catalytic converter. just over 100K miles. We looked at the O2 sensors during the replacing of the cat and they both seemed ok. I believe P0420 indicates the lower O2 sensor is switching in sync with the the upper one cos the cat isn't storing the oxygen, so it seems unlikely the sensors themselves have failed.. I think the PCM would pick up failed sensors and report their respective codes before it would report an 0420.

As mentioned above, the problem is what caused the cat to fail. I spose you could try and tell if it is blocked by disconnecting it from the exhaust manifold and seeing if the throttle response becomes much more lively.

btw if you're replacing the cat, you'll probably want a direct fit one unless you're very good at welding. Note also that most of the aftermarket direct fit ones dont really fit into the lower bracket for the stock cat, so the lower screws for the heatshield will not have anything to screw into (cos you end up having to leave the bracket off).

Be really interested if you can get it fixed under the 80,000 warranty. I think I read that stays with the vehicle regardless of the owner. Dunno how you prove the cat wasnt poisoned as penguin mentioned.
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Old 10-29-2008, 11:50 PM   #7
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I thinks it's 8 years or 80.000 miles warranty. Here you can read more about it.

As far as I know it doesn't matter the number of owners or whatever, if the cat is still stock, and your car is under the mileage, they have to replace it for free.
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Old 10-30-2008, 08:12 AM   #8
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Thanks everyone for the help.

Also do you know how much an aftermarket Cat cost?

I live in Dallas so any good places anyone can suggest?

Thanks
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Old 10-30-2008, 08:25 AM   #9
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> As far as I know it doesn't matter the number of owners or whatever,


Number of owners doesn't matter, but if the prior owner abused it, such as getting some leaded gasoline in the engine, then obviously the warranty would be void.
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Old 10-30-2008, 02:58 PM   #10
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Direct Fit ones from rockauto etc seem to go for around $200-$300. Watch out that are looking at the right one.. the zetec has a three bolt upper flange, the SPI i think has a 4 bolt.

I got one from http://wundercarparts.com

Also, don't forget the gaskets.
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