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Volkswagen Jetta 2005 and later (A5) P0420

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Last Post: Apr 4, 2016 11:12 AM Last Post By: Keithuk

Posts: 6
Registered: 04/20/13
Posted: Jun 20, 2013 12:55 AM
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Hi, I own a 2005 2.5 VW Jetta. the latest edition of that year. I have a problem with emissions as it fails smog test due to the P0420 cat below ???? bank 1?

secondary air pump works fine.
all secondary air suction hoses were replaced as they were ripped, no leaks
coolant reservoir at recommended level.
drives fine, starts on point, I'm unaware of gas mileage as tags are expired. and i do not drive it.
mileage is above 100,000 so warranty is out the window.
replaced spark plugs not too long ago.
it had other codes but i was able to fix them, then p0420 came up, cleared code, drove it for 20 miles, then it appeared again.
i have not replaced the oxygen sensors since I bough it, i do not believe they have been replaced at all.

My question is, is the cat clogged/bad and needs to be replaced? and by replacing the cat I might as well replace the o2 sensors as well right?
I had the car diagnosed for other codes, Volkswagen Beetle Golf Jetta Genuine Vw/Audi Air Pump Hose-Pump to Check Valve (Fits: Jetta 2.5)

then p0420 appeared.

any expert advise will be appreciated.

Posts: 7,661
Registered: 12/29/05
Re: P0420
Posted: Jun 20, 2013 11:24 PM   in response to: AZ in response to: AZ
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Posts: 6
Registered: 04/20/13
Re: P0420
Posted: Jul 31, 2013 12:04 PM   in response to: AZ in response to: AZ
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here is an update of the P0420. As I mentioned in my previous post, I replaced various things for other codes the car had after proper scanning. Luckily, i was able to fix those codes. After that a new code came up P0420. I did some research to such code ( cat conv below threshold bank1) based on research I was leaning on the cat as a suspect, then 02 sensors, then spark plugs, coils an such, g12 coolant was at proper level and the corespondent pressure sensor working properly. I checked all the fuses, they were all good except for the secondary air pump fuse, (40)which was misplaced. Well, that being said, after clearing the codes, I drove the car for about 25 miles and as expected ,the P0420 came back again, I took the car to a shop for a computer diagnostic, There, I learned the cat, 02 sensors, are working good. Then it hit me, after getting different codes is it possible that the ECM/PCM are to blame? Anyways, the technician cleared the codes, and advised to drive the car until the check engine light comes back, (I am confident it will) and at that time I shall take the car back to diagnose again and determine if it is the main computer faulty.
In addition, I was advised of an oil leak generated at the PVC cover and a replacement was overdue, I suspected that as I noticed I could not pull the oil dipstick out with the engine running because a major suction generated. Also, the pvc diaphragm has been ripped twice. This is a 2005 2.5 5 cyl engine A/ tranny, 121xxxx miles, the engine performance has not been compromised at all, it felt with usual power to drive.

I'll post new developments.

Posts: 12
Registered: 11/24/12
Re: P0420
Posted: Apr 4, 2016 11:12 AM   in response to: AZ in response to: AZ
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