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Amedee, Former ASE Master Technician
Category: Honda
Satisfied Customers: 26417
Experience:  ASE certified tech advanced level specialist. Wisconsin certified emissions state inspector
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1999 VW Jetta: p0422 error code

Customer Question

p0422 error code on 1999 VW Jetta that I can not clear. Any suggestions?
Submitted: 9 years ago.
Category: Honda
Expert:  Amedee replied 9 years ago.
Hello there!

There is a technical service bulletin for this code. Here it is:

26 07 04

May 14, 2007

(NNN) NNN-NNNNSupersedes T. B. Group 26 number 07-03 dated May 8, 2007 due to change in DTC description in DTC table.

MIL is ON and/or Catalytic converter is Rattling

MIL is ON, DTC P0422 is stored and/or Catalytic converter rattling.

Technical Background

The expansion mat in the original part can erode prematurely, causing the converter to rattle and/or MIL ON.

A new part was designed to fix this concern.

Production Solution

Repair identified after production was completed.


The above condition MAY be covered by the Catalytic converter Limited Extended Warranty, see Warranty Policies and Procedure Manual.

Prior to replacing a Catalytic converter under the Catalytic Converter Limited Extended Warranty, perform the following procedure:

^ Check the engine oil level.
Oil level MUST be correct.
If overfilled, level should be adjusted to the proper level prior to continuing.

Adjusting oil level is NOT covered by Warranty.


The DTC codes present will need to be erased before the test will run in MVB 46.

Is DTC P0422 (Main Catalyst Efficiency Below Threshold, Bank 1) Stored?

Check if DTC P0422 (Main Catalyst Efficiency Below Threshold, Bank 1) is stored.

^ Check if DTCs from Table are stored.

If Catalytic converter is NOT rattling and:

DTC P0422 and any DTC(s) from Table are stored:

^ Proceed to "DTCs in table are stored" (see below).

If Catalytic converter is rattling and:

Any DTC(s) from table stored:

^ Proceed to "DTCs in table are stored" (see below).

If Catalytic converter is NOT rattling and:

P0422 is the only DTC stored:

^ Proceed to "Replace Catalytic converter (see below).

If Catalytic converter is rattling and:

P0422 is the only DTC stored.

No DTCs are stored:

^ Proceed to "Replace Catalytic converter" (see below).

DTCs in table are stored:

The reason for DTC(s) from Table MUST be corrected (possibly at customer expense) prior to potential Catalytic converter replacement.

With other DTC(s) corrected:

If Catalytic converter is rattling:

^ Proceed to "Replace Catalytic converter" (see below).

If Catalytic converter is NOT rattling:

^ Erase all DTC(s) and set readiness code.

If complete readiness code cannot be set due to the catalyst diagnosis monitor in display group 46 not resetting:

^ Proceed to "Replace Catalytic converter" (see below).

If complete readiness code can be fully set:

Return vehicle to the customer without replacing Catalytic converter.

If vehicle was returned to the Customer (without converter replacement) and Customer returns with DTC P0422 stored again:

^ roceed to "Replace Catalytic converter" (see lo
Replace Catalytic converter


Catalytic converter Limited Extended Warranty:

Required Parts and Tools

When replacing any catalyst, your VIN may be required to ensure the correct part is ordered (check with your Parts Dept.).

Parts submission:

If Catalytic converter is on parts submission:

^ Att


Claims for s (which are on submission) that are shipped to the Warranty Test Center without print-outs (including freeze frame data) may be denied.

Additional Information

All part and service references provided in this Technical Bulletin are subject to change and/or removal.

Always check with your Parts Dept. and Repair Manuals for the latest information.

Amedee and other Honda Specialists are ready to help you
Customer: replied 9 years ago.
I had this issue since early november and the catalytic converter as well as the downstream O2 sensor have been replaced. As soon as the sensors go to ready the code comes back up immediately. Usually 3 drive cycles. Oil level has not been an issue. I've checked for grounding issues but can not find where the O2 sensors are grounded from the basic wiring diagram I have. Unless the housing is grounded through the exhaust and it has lost its ground???
Expert:  Amedee replied 9 years ago.
What kind of converter did you replace the old own with? Did you use O.E.?

What about exhaust leaks? Are there any?

Any o2 sensor codes that come up along with the converter code?
Customer: replied 9 years ago.
I had exhaust leaks and initially I thaught that was the root of the evil. I took the car to a muffler shop and they welded and replaced some pipe to fix the leaks. They later checked the code and then replaced the catalytic converter. As far as O.E. not sure, I suspected they knew what they were doing due to exhaust is all they do. May be wrong though?

The code came back anf then replaced the O2 sensor but no actual O2 sensor codes have come up, just the P0422 (efficiency) code

But before the leaks were fixed there was a pending (If i remember corectly) P0102 MAF circuit low input. I checked the MAF and have not had this one come back yet.
Expert:  Amedee replied 9 years ago.
OH.. THey did this at a muffler shop?

They probably used a browns recycling converter! NOT GOOD ENOUGH!


You will need to get one from the dealer and put it on!
Customer: replied 9 years ago.
I am going to call the shop tomorrow to get the manufacture and part number of the conveter. The odd thing is the tech mentioned that the catalytic converter that he replaced was not an O.E. converter. That one was installed May 2004.
Expert:  Amedee replied 9 years ago.
That may very well be why the code was on in the first place!

When you call, they are going to tell you that it is ok for after market converter to go on cars. Don't believe a word of it!

The newer obd2 parameters are so tight, that the computer will pick up the difference with the after market converter and set this code!

Also, in the tsb, it goes into saying that there is a new part that was designed to fix this problem. CALL THE DEALERSHIP AND GET THIS NEW PART AS SPECIFIED IN THE TSB!
Customer: replied 9 years ago.
I will give a dealer a call tomorrow regarding the converter. Do you have TSB# XXXXX reference?

I would also like to mention that the car was taken to a VW dealer a few weeks ago for inspection after the converter was replaced. The sensors must have just came to ready and the error came up. Failed inspection and they had told me that the resonator and mufler also need replacing? I don't understand what that would have to do with emissions?
Expert:  Amedee replied 9 years ago.
The tsb number is XXXXX 07 04

If the exhaust is leaking, it will give the computer false o2 readings. This might result in your code.
Customer: replied 9 years ago.
I can't seem to pull up the images for the FSB above. Can you resend the FSB for the Jetta please?
Expert:  Amedee replied 9 years ago.

Customer: replied 9 years ago.
Got the car back from the local VW dealer this last Wednesday where they replaced the catalytic converter ($900 plus). It is now Saturday and the check engine light came back on with same code?????????????
Expert:  Amedee replied 9 years ago.
Did you have them install the new part per TSB?

The expansion mat in the original part can erode prematurely, causing the converter to rattle and/or MIL ON.

A new part was designed to fix this concern.

Customer: replied 9 years ago.
I called one dealer and they they looked at the TSB. They stated that there was no part numbers on the bulletin for a catalytic converter. Is the expansion mat inside the catalytic converter? Or is this an extra part? Where is it located?
Expert:  Amedee replied 9 years ago.
Not sure! Just going by the TSB.

The guys at the dealer should know this TSB.

You said you replaced the down stream o2 sensor? Did you use O.E? Or was it an after market part?

Now that you have a brand new cat, I would be very suspicious of those o2 senors! WOuld not be a bad idea to change them!

I have heard of small vacuum or air leaks causing this code. You might want to ask the guys at the dealership what you short and long term fuel trims are at?

Also, you would not happen to have a Performance chip plugged in to your car any where.. would you?

Anything after market at all? Performance intake or exhaust or anything like that?
Customer: replied 9 years ago.
Yes the downstream O2 was replaced with an OEM part.

Performace chip or performance upgrades-- the car is not worth putting such parts on. All Stock

I still do not believe that the catalytic converter is bad. Below are a couple sites that say there could be problems with the upstream sensor. But if that was the case would I not get a different code. Is there anyway easy way you know to test the sensors? It gets costly trying to replace parts to pinpoint the problem part. Also do you think it may be the computer?
Expert:  Amedee replied 9 years ago.
I do not think it can be the computer. But I could be wrong.

To test the o2 sensor parameters, you need a scan tool.

But you can watch the o2 sensor voltage with a voltmeter and see if is stuck one way or the other. This will also tell you if there is any air leaks or vacuum leaks causing the engine to run lean. If that is the case, the o2 sensor will not fluctuate like it should and will mirror the rear o2 sesnor and then cause the converter code.
Customer: replied 9 years ago.
Are the downstream and upstream O2 sensors the same? I still have the downstream sensor that I changed out (don't think that it is bad) with the upstream. It may give me an indication if that one is bad. I have one of the cheap scan tools.

Vacuum leaks, oh where to start. 6 months ago I had problems inspecting the car in a different state. Tuned teh car up (ran like it never run before) and still had a misfire on one of the cylinders. Found a bad vacuum hose up front and replaced it. Still had to take it to the dealer where they found another leak on one of the rear hoses. Also found that the after market radio was causing bad comunication with the OBDII.

Air Leaks??? what are you talking about. Exhaust, intake??
Expert:  Amedee replied 9 years ago.

Up stream o2 sensor is before the converter. Downstream o2 sensor is after the converter.

Air leak is after the mass air flow sensor and before the throttle body. Vacuum leak is air leak behind the throttle body.

Exhaust leaks will cause o2 sesnor reading to be off. This can cause converter codes and o2 sensor codes. But I think you did tell me that there are no exhaust leaks. So we I believe we did cover that.
Customer: replied 9 years ago.
I know where the O2 sensors are. Since the downstream sensor was already replaced I would fucus on the upstream One. As you stated before "I would be very suspicious of those o2 senors!". If I can take the one I took off downstream of teh cat and put it on the upstream position then it would verify that that one is either good or bad?

My question is do both downstream and upstream sensors function the same?

Already checked for air leaks between the throttle body and MAF -- none

Vacuum leak -- I can check again but didn't notice anything originally
Expert:  Amedee replied 9 years ago.
YES! THey both function the same!

The only thing is that if the check engine light came on with the one sesnor that you want to take off the teh cat, this one might be bad. BEcause this is the sensor that was on there to begin with causing this code... correct?
Customer: replied 9 years ago.
No, the downstream sensor that is on the car now is brand new. It was replaced after the Catalytic converter was initially replaced at the muffler shop. I did not think it was bad then and I still don't think it is. Now the car has 2 new catalytic conveters on and new downstream O2 sensor. Check engine Light is still on.
Expert:  Amedee replied 9 years ago.
We have covered all the basics and more on your vehicle.

I tried to help you out.

I will leave this question open for other experts to assist you!

Thanks for being patient.