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Old 12-11-2011, 02:00 PM
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Default Check Engine. Got P0420 on the scanner.

2002 2.0 Automatic.
Anybody had this one before? O2 sensor or catalytic converter? Or something else?
Suggestions please.
As always, thanks.
Rob

Last edited by UNCC49er; 12-11-2011 at 02:02 PM. Reason: Added engine and year.
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Old 12-11-2011, 04:01 PM
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i believe this code is for the post cat 02 sensor
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Old 12-11-2011, 04:25 PM
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I also have a 2002 2.0 automatic and I've had this code. Haven't taken care of it though so i don't know if it's a serious code or just one that likes to appear every now and then.
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Old 12-11-2011, 05:49 PM
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I think it's something with air intake because someone else made a thread about it and fukn answered then as a joke I was like "lol that's ironic 420 and it's about air intake" but yeah po135 is pre cat and po235 is post cat o2 sensor...I think. Lol I'm kinda sure but yeah. Not saying it is then I'm wrong but I'm 99% sure
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Old 12-12-2011, 04:02 PM
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Hello,

I have this code (P0420) as well. I believe this code indicates that its the catalytic converter working at below efficiency. This might make sense as the car has 115,000 miles and I had a series of bad ignition coils that caused misfires that could very well have degraded the catalytic converter.

However, it could be the O2 sensor - so how do I figure out whether or not its the sensor or the converter?

A new catalytic converter from VW is $1010.00, which is outrageous to say the least. My question is this: What about third party catalytic converters? Why are they so cheap, and will they work?

Example #1: MagnaFlow Catalytic Converters - 49-STATE & CANADA Catalytic Converters For Trucks, Suv's, American Muscle, Diesel, & Sport Compact Vehicles

Example #2:
Amazon.com: Magnaflow 53035 Universal Catalytic Converter (Non CARB compliant): Automotive Amazon.com: Magnaflow 53035 Universal Catalytic Converter (Non CARB compliant): Automotive

Example #3:
Amazon Amazon

Example #4: Volkswagen Jetta 1.8T Catalytic Converter 2001 2002 2003 OBDII Stainless | eBay

Any advice would be appreciated.

Thanks,
CH
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Old 12-12-2011, 09:38 PM
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P0420= Catalyst System; Bank 1: Efficiency Below Threshold

It could be a leak in the intake/exaust, the 02 sensor or a bad catylitic converter.

More than you wanted to know about 02 sensors: http://mr2.com/TEXT/O2_Sensor.html


Check out this link for some more information. VWVortex.com - Aftermarket DP/Cat -DTC - Cat efficiency below threshold - Who has this DTC and wich DP/Cat

Also, I think there may have been a recall on the converter. Call a dealer and check to see if your car has had all the recalls performed. And if in fact, the converter was recalled. good luck.


Last edited by 01GTiVRSICK; 12-12-2011 at 09:44 PM.
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Old 12-13-2011, 06:59 AM
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Quote:
Originally Posted by 01GTiVRSICK View Post
P0420= Catalyst System; Bank 1: Efficiency Below Threshold

It could be a leak in the intake/exaust, the 02 sensor or a bad catylitic converter.

More than you wanted to know about 02 sensors: Oxygen Sensor Information


Check out this link for some more information. VWVortex.com - Aftermarket DP/Cat -DTC - Cat efficiency below threshold - Who has this DTC and wich DP/Cat

Also, I think there may have been a recall on the converter. Call a dealer and check to see if your car has had all the recalls performed. And if in fact, the converter was recalled. good luck.

Thanks, I already called VW stealership - no recalls on the 1.8T, only on the 2.0L.

- CH
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Old 12-14-2011, 10:58 AM
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The cost to fix this vs staring at a check engine light is ridiculous. A new catalytic converter from the stealership is, as stated, over $1000. The "test pipe" I had installed? $25. The two O2 sensors I replaced? $250 total.
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Old 12-14-2011, 11:30 AM
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find someone that programs to hook up your car and write out the rear o2 file. i paid $50 to have it done. i dont even have my rear o2 sensor plugged in. no cel.
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Old 02-02-2012, 10:34 AM
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My cel just came on yesterday and it is the 0420 code. I cleared it with the scanner and it hasn't come back on. I don't suppose there is a way to check a cat to see if its flowing & working properly so judging by the 95k miles its probably that? My friend has a Mercedes w/120k and the cat was restricting to the point the car ran rough. We "took care of the problem" and now it runs great, what do you know?
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Old 02-02-2012, 04:04 PM
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2004 w/ 95k miles is probably covered under the extended warranty.
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Old 02-02-2012, 04:10 PM
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The cat isn't restricting, it's just not "fixing" the air exiting the cat to the sensors liking.

Pulling it out won't alleviate anything.
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Old 02-02-2012, 05:07 PM
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O2 Sensor Spacer im running one of these on an after market cat. cat was new and threw the code i now the o2 sensor was good because i had replaced it prier to me owning the golf. threw the 42 dd o2 spacer on problem solved. i had picked the spacer up locally so i only paid $40. for it.
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