# Error code: P420 for catalytic converter. Car under warranty. Dealer says no such code.



## nick7193 (Feb 1, 2011)

Hi everyone,
I am confused and stuck here.
I have a 2004 Jetta. 2.0 L, Engine Code: BEV - Mileage: 70270
Car inspection is due this month. CEL came on and went back off twice by itself.
There is no CEL right now.
Yesterday when I attached a friends MODIS and checked it still showed error code : P420
Which is for catalytic converter.
Today I went to dealer to get it done as it is still under warranty untill 80,000 or 8 years.
They checked everything and now they say there is no such code, infact now they tell me there is an error code for brake vacuum pump and asked $570 for the job.

I am concerned because I think they do not want to do it for free. My warranty expires on October 13th 2011.
I took the car to inspection today and it got rejected because systems were not ready.
Oxygen Sensors: NOT READY
I think they erased and reset the system.
What should I do?


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## nick7193 (Feb 1, 2011)

This particular system was used to diagnose the code


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## rommeldawg (May 25, 2009)

well warranty doesnt really cost the "dealer" ... the tech loses out some since it doesnt pay as much. i havent worked for a dealer ship but family owned one and have friends that do. anyway if they havent cleared the codes there will still be information stored as pending or intermittent. see if you can get vag-com but really modis should be able to read it. we use pcretriever and vag-com for vw though.


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## FL 2.0L (Aug 1, 2002)

Try P0420. They should know better. Something doesn't sound right.


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## tdogg74 (Mar 1, 2002)

P0420 

Technical Description 

Catalyst System Efficiency Below Threshold (Bank 1) 
What does that mean? 

The catalytic converter has an oxygen sensor in front and behind it. When the vehicle is warm and running in closed loop mode, the upstream oxygen sensor waveform reading should fluctuate. The downstream O2 sensor reading should be fairly steady. Typically the P0420 code triggers the Check Engine Light if the readings of the two sensors are similar. This is indicative of (among other things) a converter that is not working as efficiently as it should be (according to specs). It is part of the vehicle emissions system. 
Symptoms 

You will likely not notice any drivability problems, although there may be symptoms. 
Causes 

A code P0420 may mean that one or more of the following has happened: 

Leaded fuel was used where unleaded was called for 
An oxygen sensor is not reading (functioning) properly 
The engine coolant temperature sensor is not working properly 
Damaged or leaking exhaust manifold / catalytic converter / exhaust pipe 
Retarded spark timing 
The oxygen sensors in front and behind the converter are reporting too similar of readings 

Possible Solutions 

Some suggested steps for troubleshooting a P0420 error code include: 

Check for exhaust leaks at the manifold, pipes, catalytic converter. Repair as required. 
Use a scope to diagnose the oxygen sensor operation (Tip: The oxygen sensor in front of the catalytic converter normally has a fluctuating waveform. The waveform of the sensor behind the converter should be more steady). 
Inspect the downstream heated oxygen sensor (HO2), replace if necessary 
Replace the catalytic converter 

One thing to note is that many vehicle manufacturers offer a longer warranty on emissions-related parts. So if you have a newer car but it's out of it's bumper-to-bumper warranty, there still may be warranty on this type of problem. Many manufacturers give a five year, unlimited mileage warranty on these items. It's worth checking into.


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## Glegor (Mar 31, 2008)

i wonder if you could temp. fix the issue with a o2 sensor spacer/j pipe?


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## nick7193 (Feb 1, 2011)

Hey guys thanks for all the replies...
Couldn't get to forums for past few days because of the hurricane.

Anybody near 07047 who might be able to help?
And I don't have VAG-COM

As the car is still under warranty for emissions, I would like the dealer to change the catalytic conveter. It costs way too much I heard.
Does anybody have any idea how much would it cost. Part+ Labor?


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## nick7193 (Feb 1, 2011)

Also, if someone can tell me what kind of VAG-COM software do i need?

Sorry for this question but I am not familiar with this


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## ps2375 (Aug 13, 2003)

Software is not the issue, as you need the Vag-Com cable for it to work. Software is a free download.


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## nick7193 (Feb 1, 2011)

ps2375 said:


> Software is not the issue, as you need the Vag-Com cable for it to work. Software is a free download.


 Yes sir, i just downloaded the software VCDS LITE.
would you be kind enough to tell me what vag-com cable should i buy? It says it is compatible with 3rd party cables, so i assume i can find something on ebay. But what exactly am I looking for?


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## ps2375 (Aug 13, 2003)

There was a cable in the classifieds not too long ago. I would recommend an actual Vag-Com cable. as you won't get too much help with one of the copies.


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## Anony00GT (Mar 6, 2002)

Get the actual Ross-Tech cable. 

I work in 07866 and live in 07843, maybe 40 minutes from you. I've got a full VCDS, and can help you if you want for cheap if you're willing to make the trip out to me. 

BTW, if the MODIS you've got access to has the European software package, it should be able to do most of the diagnostic VAG functions that the VCDS can do, it's just much less user-friendly.


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## nick7193 (Feb 1, 2011)

Sounds good! Let me know what u want and when can we do it...


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## nick7193 (Feb 1, 2011)

I'll take the advice and get an original cable. But I have never used it before and would need some help... And this is the only place to get all the help.... Thanks all you guys... 
I will again check the codes with MODIS tomorrow and post the results


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## ps2375 (Aug 13, 2003)

the dealer will want to do their own diagnosis whether you scan it with modis or Vag-Com. They don't really care what you think the issue is, they have to go thru their own diagnosis with their system and come to their own results, what you tell them means absolutely nothing. If you are buying Vag-Com to move this along, don't, it won't help you with the dealer.


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## Anony00GT (Mar 6, 2002)

ps2375 said:


> the dealer will want to do their own diagnosis whether you scan it with modis or Vag-Com. They don't really care what you think the issue is, they have to go thru their own diagnosis with their system and come to their own results, what you tell them means absolutely nothing. If you are buying Vag-Com to move this along, don't, it won't help you with the dealer.


 That is correct, but if you want to diagnose the problem yourself then the VAG-COM is the way to go. If you're under that 8/80 time frame and the vehicle is stock, and you've definitely got a P0420, they definitely should warranty it...in fact, they have to under federal law. 

That being said, there are other things that can cause P0420 besides a bad catalytic converter.


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## germancarnut51 (Mar 23, 2008)

My experience is with MKIIIs, MKIVs may work differently. But, on a MKIII the problem could be a defective O2 sensor, and not a defective cat. You would not see a CEL until the Readiness Tests have been completed, if the battery has been disconnected. 

I know that some people on this Board suggest disconnecting the battery to erase the ECU memory, then running the car down for emissions testing so the CEL will not be on, claiming that the inspection station will pass the car if the CEL is not on. Some States will not pass a car unless the CEL is off, the Readiness Tests are completed, and a Scan can be completed successfully without the CEL lighting. Wiping out the ECU memory is not a solution in those States (including CA). 

What I would suggest doing is take your scanner, and check to see if it can read the output of the O2 sensors, and watch them as they warm up. Are they working correctly? Look to see if the O2 Heater Test is completed. If the Heater Test is not completed, then the O2 Sensor Test cannot be completed, and the Cat Tests cannot be completed.


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## nick7193 (Feb 1, 2011)

Ok I am going to check the codes tomorrow morning after I do the spark plugs and wires.
Any suggestions what exactly am I looking for when I scan with MODIS.
as said earlier there are two O2 sensors I believe. How much would they cost? Any ideas?
Guys all this help is greatly appreciated, really!


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## germancarnut51 (Mar 23, 2008)

nick7193 said:


> Ok I am going to check the codes tomorrow morning after I do the spark plugs and wires.
> Any suggestions what exactly am I looking for when I scan with MODIS.
> as said earlier there are two O2 sensors I believe. How much would they cost? Any ideas?
> Guys all this help is greatly appreciated, really!


Having a scanner or having access to a scanner doesn't do you any good if you don't know how to use it. I recommend reading the manual for the scanner so you will know what individual functions it has.


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## nick7193 (Feb 1, 2011)

*Test Results*

Hi all,
We just checked the codes again and have two codes present (which we erased)

(1) P0420 - Catalyst System Efficiency Below Threshold (Bank 1)

The readings were as follows:
Bank 1 Sensor 1 (V) - 1.600
Bank 1 Sensor 2 (V) - 0.440

After a little while it fluctuated to

Bank 1 Sensor 1 (V) - 1.520
Bank 1 Sensor 2 (V) - 0.435

After a little while

Bank 1 Sensor 1 (V) - 1.200
Bank 1 Sensor 2 (V) - 0.440

-------------------------------------------------------------
Bank 1 Sensor 1 value - 3
Bank 1 Sensor 2 value - 4

after a while

Bank 1 Sensor 1 value - 7
Bank 1 Sensor 2 value - 0

after a while

Bank 1 Sensor 1 value - 3
Bank 1 Sensor 2 value - 0

(2) P1429 (VW error code: 17837)

Brake Vacuum Pump/Circuit Problem

What do you think guys


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## Glegor (Mar 31, 2008)

i would believe the secondary o2 sensor to be failed, or failing..


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## nick7193 (Feb 1, 2011)

tdogg74 said:


> P0420
> 
> Technical Description
> 
> ...


Hi, 
According to this secondary O2 sensor should be fairly steady... Mine seems to be steady.

You still think it might be bad or going bad?


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## germancarnut51 (Mar 23, 2008)

nick7193 said:


> Hi,
> According to this secondary O2 sensor should be fairly steady... Mine seems to be steady.
> 
> You still think it might be bad or going bad?


The problem is that the #2 O2 sensor readings are too low. Either the O2 sensor is defective, or you're writing/reading the number wrong, or there is something wrong with the scan tool or the ECU port sending the information.


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## nick7193 (Feb 1, 2011)

As earlier MODIS was used to diagnose.
Can someone with a VAG-COM help?
I have no clue what to do now. Should I change the #2 o2 sensor or what?
I have to get the insoection done by the end of this month


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## ps2375 (Aug 13, 2003)

I believe (but been a while since I had access to the Bently on CD) that the diagnosis of this code on the mkIV 2.0's said that if you have this code and no secondary O2 sensor code, that the CAT is failing and should be replaced. You could also try the plug non-fouler trick.


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## Glegor (Mar 31, 2008)

ps2375 said:


> I believe (but been a while since I had access to the Bently on CD) that the diagnosis of this code on the mkIV 2.0's said that if you have this code and no secondary O2 sensor code, that the CAT is failing and should be replaced. *You could also try the plug non-fouler trick.*


mind elaborating on that?


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## ps2375 (Aug 13, 2003)

That is the spacer that moves the sensor out of the air flow and makes the ECU think the cat is working better than it is. I have done it a couple of times on 1.8t's and it seems to work well.


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## nick7193 (Feb 1, 2011)

ps2375 said:


> I believe (but been a while since I had access to the Bently on CD) that the diagnosis of this code on the mkIV 2.0's said that if you have this code and no secondary O2 sensor code, that the CAT is failing and should be replaced. You could also try the plug non-fouler trick.


I'll keep this as the last resort if the dealer doesn't change the cat converter. But how is it done?
And also the dealer just erased all the codes on my car and handed it back to me... Why? And what can I do about it? Can I get a print out of codes and take it to the dealer?


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## Keithuk (Nov 17, 2009)

Yes P420 must be a typo or a miss read but as mensioned there is a P0420.

*EOBD II Error Code:* P0420

*Fault Location:*
Catalytic converter system, bank 1 - efficiency below threshold

*Possible Cause:*
Malfunction indicator lamp (MIL) Non Emission Fault - No warning light.
Catalytic converter.
Wiring.
Heated oxygen sensor (HO2S) 2 (G39).

*Possible Solutions:*C
Check for exhaust leaks at the manifold, pipes, catalytic converter. Repair as required.
Use a scope to diagnose the oxygen sensor operation (Tip: The oxygen sensor in front of the catalytic converter normally
has a fluctuating waveform. The waveform of the sensor behind the converter should be more steady).
Inspect the downstream heated oxygen sensor (HOS2) (G39), replace if necessary.
Replace the catalytic converter.

As taken from my Free EOBD II Fault Codes Software.


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## Glegor (Mar 31, 2008)

nick7193 said:


> I'll keep this as the last resort if the dealer doesn't change the cat converter. But how is it done?
> And also the dealer just erased all the codes on my car and handed it back to me... Why? And what can I do about it? Can I get a print out of codes and take it to the dealer?


you buy the J pipe, or spacer, remove the rear o2 sensor, install spacer/j pipe, re-install 02 sensor in its new location in the j pipe/spacer.

all that either one of those devices does, is move the 02 sensor out of the direct stream of exhaust gas. it puts it out of the way a bit, so it doesnt see as much exhaust passing by it..

they work good enough that you can REMOVE the catalytic converter from a vehicle, and if you have one of these installed on the rear o2 sensor, most of the time, it wont throw a code


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## Obi-Wan (Sep 12, 2009)

Rrrrriiiight.... 
What's a J-Pipe? and who's got 'em?


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## nick7193 (Feb 1, 2011)

Yeah i cant find one either... Can any body find a picture of it so we know what we're looking for


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## sun98gtiVR6 (Jan 7, 2007)

Obi-Wan said:


> What's a J-Pipe? and who's got 'em?


would also like to know


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## linchpin.666 (Apr 15, 2010)

This might work for you passing emissions (depending on your state), but won't actually FIX the problem. 

Here's the spacer they're talking about:
http://store.42draftdesigns.com/O2-Sensor-Spacer_p_306.html

This attaches to your catalytic converter, and the 02 sensor attaches to it. It's basically tricks the sensor into thinking the emission system is working correctly by moving it further away from what it's supposed to be sensing. A lot of people use them on aftermarket exhausts that actually pass emissions, but pop a CEL anyway.


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## gtiswapped96 (Dec 6, 2009)

Blackforestindustries.com has the o2 sensor spacers...give emm a shot


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## germancarnut51 (Mar 23, 2008)

Why would you want to spend money to buy a part, and trick a malfunctioning emissions system inorder to pass an emissions test?

You should be under two warranties on your car. The standard VW Warranty, and the seperate Warrabty (with an extended mileage and period) required by the Federal Government on the Emissions System). 

I'd take the car in and have it emissions tested so it will fail. Now you have independent verification that the emissions system is failed, and the VW Dealer will not be able to deny your warranty claim even if you go past the expiration of the warranty period because you can prove that you were there for service for that problem. You would even be able to complain directly to VW AG.


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## nick7193 (Feb 1, 2011)

germancarnut51 said:


> Why would you want to spend money to buy a part, and trick a malfunctioning emissions system inorder to pass an emissions test?
> 
> You should be under two warranties on your car. The standard VW Warranty, and the seperate Warrabty (with an extended mileage and period) required by the Federal Government on the Emissions System).
> 
> I'd take the car in and have it emissions tested so it will fail. Now you have independent verification that the emissions system is failed, and the VW Dealer will not be able to deny your warranty claim even if you go past the expiration of the warranty period because you can prove that you were there for service for that problem. You would even be able to complain directly to VW AG.


I'm going to get the car inspected tommorow, lets see what happens.
Only thing i'm concerned is they will say oxygen sensors are bad and will make me pay a lot of money anyways... What do u think?


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## nick7193 (Feb 1, 2011)

The car passed the inspection!
I am starting to wonder if the misfire triggered P0420. 
After I did new coil pack and spark plugs and wires, car runs strong and it didnt fire CEL since then.
I'm still going to check the codes on the car tommorow just to be sure.
All the help is greatly appreciated guys.
VWVORTEX is the best!


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## nick7193 (Feb 1, 2011)

I checked again today and there are no codes present!


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