2001 Jetta - P0420 - VW Forum :: Volkswagen Forum
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post #1 of 10 (permalink) Old 08-30-2012, 09:31 AM Thread Starter
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2001 Jetta - P0420

I have a 2001 Jetta:

4 Cyl AZG motor:

I currently have a OBDII Code of P0420 - Catalyst System Efficiency Below Threshold (Bank 1)

About a year ago, I replaced the Thermostat after running through the winter with it broken:

For the last year, I have been dealing with misfires. I recently replaced:

Coil:
Wire:
Plugs:

I Cleared the codes, after 200 miles the P0420 code came back:

The car idles slightly rough and overall it has a "Sweet" smell when running.

Does anyone have any thoughts? Do you think the cat is just bad?
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post #2 of 10 (permalink) Old 08-30-2012, 09:34 AM
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The 420 code hmmm...has she smoked a blunt today?

If not, LIGHT IT UP!

lol...I think that code might be for a 02 sensor. Not sure. Maybe someone else knows for sure. Just got to wait for a reply.


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post #3 of 10 (permalink) Old 08-30-2012, 10:44 AM
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0420 refers to Post O2 sensor under the car on passenger side. I got mine from Autozone about 70 - 80 bucks for a bosch. Not that hard to replace, takes about an 30 mins to an hour if you already have parts and car is cooled off.
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post #4 of 10 (permalink) Old 08-30-2012, 10:49 AM
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Maf could cause al of this as well, clean it.


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post #5 of 10 (permalink) Old 08-30-2012, 10:53 AM
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I'd just do a tune up since you did half of it already. Clean MAF. Pre and Post cat 02 sensors. Fuel Filter. Put some fuel injection cleaner in the gas.


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post #6 of 10 (permalink) Old 08-30-2012, 01:18 PM Thread Starter
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I will clean the MAF tonight..


Next item I guess will be to change the downstream O2 Sensor. But since I know the engine is not running properly, smell and rough idle, I doubt it would be the O2 sensor.

Thanks for your suggestions:
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post #7 of 10 (permalink) Old 08-30-2012, 01:57 PM
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P0420 is for a bad catalytic converter. If the downstream o2 sensor was bad, there would be a different code.

Leave the MAF sensor alone. Cleaning it can screw if up if you don't use the right stuff.
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post #8 of 10 (permalink) Old 08-30-2012, 02:00 PM
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if you are running a aftermarket cat, the second o2 sensor will still throw a code.

ive had mine replaced when it went bad and the new one set a code, so i got one of these...O2 Sensor Spacer
however they say no longer available...

http://www.energeticforum.com/renewa...n-foulers.html
try this.


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Last edited by truefire04; 08-30-2012 at 02:02 PM.
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post #9 of 10 (permalink) Old 08-30-2012, 04:02 PM
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Quote:
Originally Posted by 2001Jettagls View Post
P0420 is for a bad catalytic converter. If the downstream o2 sensor was bad, there would be a different code.

Leave the MAF sensor alone. Cleaning it can screw if up if you don't use the right stuff.
of course you use MAF cleaner, what else would you use? Dawn or palmolive? lol!
yo ucould have an vac leak, faulty injectors, spark plugs, exhaust leak, etc, etc.
Is there another code with it or is this the only code thrown?

FYI:


The Engine Control Module (ECM) monitors the switching frequency ratio of heated oxygen sensors 1 (front O2 sensor) and heated oxygen sensors 2 (rear O2 sensor).

A three way catalyst converter (Manifold) with high oxygen storage capacity will indicate a low switching frequency of heated oxygen sensor 2. As oxygen storage capacity decreases, the heated oxygen sensor 2 switching frequency will increase.

When the frequency ratio of heated oxygen sensors 1 and 2 approaches a specified limit value, the three way catalyst malfunction is diagnosed.


Read more: http://engine-codes.com/p0420_volksw...#ixzz2548AJpka


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post #10 of 10 (permalink) Old 08-31-2012, 05:37 PM
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I've had customers use carb cleaner on a MAF and ruined it instantly.

That why I said to be sure to use the proper stuff. It's Very delicate sensor and easily damaged.

If you get a flat tire, changing the engine oil won't fix the problem.

If you get a P0420 code, cleaning the throttle body won't clear that code.

Psst, You gave some good info above, the OBDII codes are really an easy way to point you in the right direction to fix the car the first time.
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