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STILL STRUGGLING TO CURE CODE P0420.


Wrinkly
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Have had many submissions in this section about my 2005 S Type 2.5 Petrol, with many suggestions and quite a few new parts fitted. BUT still get that Code P0420 "Catalyst System Efficiency Below Threshold. Bank 1.

Having reviewed the situation and the actions that have been taken, I then came upon an article which may/may not be relevant and would appreciate comments and or suggestions from those who are well informed and have given advice on the matter previously.

Part of my "reviewing the situation" (any of you from the era when that phrase was used in a hit song), was that the article I found this week referred to misfire can cause severe damage to the Catalytic Converter. This interests me on the basis that just prior to P0420 raising its "ugly head", I had an incident where the car went into restricted mode due to a misfire on No3 Cylinder. This is of course in Bank 1 where the P0420 code is reported. At the time all Six Plugs (Denso) were renewed along with Six Coil Packs (expensive) and all Six Inlet Manifold Gaskets (Jaguar genuine) were also replaced. The car was also fully serviced (and I mean fully, all oils, filters etc etc were replaced that was at 62000 miles approx.). The car has done about 1000 miles since then and repeatedly throws this P0420 Code. If reset it will run for about 18 - 20 miles before showing in again. What is annoying is that the car does not present any of the usual signs of Cat failure, I.E. smelly exhaust, misfire, high fuel usage (mpg), lack of power etc, etc. "It just runs as sweet as a nut", thankfully. I am of an age and being that a yellow engine warning light really "chesses me off big time", and I need to cure it.

I have been reluctant to replace the Catalytic Converter on Bank 1, due to their cost if you buy recognised parts and I do not ever by cheap replacement parts, because I do not consider them cheap in the long run. However having read the recent article suggesting that a misfire will "Kill the Cat" I am beginning to think it might be the best route to go. I am therefore seeking views/opinions/thoughts either for or against taking this action of replacing the Cat. The other question is do I replace the one Cat, or do I "bite the bullet" and have both of them replaced.

 

Many thanks for you considerations/advice/views/suggestions.

Regards and Best Wishes, John

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Hi John

A quick look through the 'tinternet' and come up with this list (which looks to me to be quite definitive)

My money is on item number 3 and can easily be checked by getting your garage to check the oxygen levels from the exhaust (e.g. and exhaust leak will produce a high O2 level on exhaust emissions.....it should be near to zero).

If the exhaust is leaking then this will throw an imbalance on the cat threshold (pre and post levels).
This would indicate a leak in the primary part of the exhaust (more than likely a joint before or after the cat - where the pipes/manifold meet the cats)

What repairs can fix the P0420 code?
  1. Replace muffler or repair leaks in the muffler.
  2. Replace exhaust manifold or repair leaks in the exhaust manifold.
  3. Replace exhaust pipe or repair exhaust pipe leaks.
  4. Replace catalytic converter (most common)
  5. Replace engine coolant temperature sensor.
  6. Replace front or rear oxygen sensor.
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Thanks for info. Just as a matter for consideration both upstream and downstream Lambda have had new fitted. I will get my son in lae to take the car to work where they have an MOT testing station and I am sure he can get the oxygen levels checked.

Regards, John

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having given thought to the above suggestion I am probably being very stupid but what I am having a problem understanding is that after the two Lambda Sensors (up and down stream) there are to the best of my knowledge no other Sensors in the exhaust. If that be the case then how does the "Efficiency Below Threshold" get read and eventually produce a code. The sensors being brand  new are plainly working so where is the possibility of too much air being calculated from?

Cheers, John

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  • 7 months later...
On 10/21/2021 at 7:05 PM, Wrinkly said:

having given thought to the above suggestion I am probably being very stupid but what I am having a problem understanding is that after the two Lambda Sensors (up and down stream) there are to the best of my knowledge no other Sensors in the exhaust. If that be the case then how does the "Efficiency Below Threshold" get read and eventually produce a code. The sensors being brand  new are plainly working so where is the possibility of too much air being calculated from?

Cheers, John

I would love to know how this all panned out as I have P0430!
 

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15 hours ago, Papa Wilko said:

I would love to know how this all panned out as I have P0430!
 

Andrew

The cat did eventually cure the problem. That was the last stage of many including inlet manifold removed to fit new plugs and new ignition coils and six new manifold gaskets. Also previous to the inlet off I had fitted both new Lambdas (one at a time and testing after each individual Lambda was fitted. The car had a slight misfire before my P0420 codes started. That in itself can kill the Cat, which it eventually proved had happened.

Word of advice if you decide to go a similar route: always use genuine manifold gaskets (Jaguar, in my engine there were six separate gaskets), always use Denso Lambda`s (Denso being OE equipment) and always purchase a good quality/dearer Catalytic Converter.  Cheap East Asian products do not work well on Jaguar engines.

If any other advice needed or questions to ask, please feel free to contact me.

Good Luck with sorting your problem.

Best Wishes and Regards, John

 

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  • 3 weeks later...
On 5/30/2022 at 11:51 AM, Wrinkly said:

Andrew

The cat did eventually cure the problem. That was the last stage of many including inlet manifold removed to fit new plugs and new ignition coils and six new manifold gaskets. Also previous to the inlet off I had fitted both new Lambdas (one at a time and testing after each individual Lambda was fitted. The car had a slight misfire before my P0420 codes started. That in itself can kill the Cat, which it eventually proved had happened.

Word of advice if you decide to go a similar route: always use genuine manifold gaskets (Jaguar, in my engine there were six separate gaskets), always use Denso Lambda`s (Denso being OE equipment) and always purchase a good quality/dearer Catalytic Converter.  Cheap East Asian products do not work well on Jaguar engines.

If any other advice needed or questions to ask, please feel free to contact me.

Good Luck with sorting your problem.

Best Wishes and Regards, John

 

Now keep getting intermittent  P0420 readings, even after all I have done.

ANY IDEAS FROM ANYONE / ANYWHERE

Cheers , John

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  • 3 weeks later...

Hi with that code and what you have  what done. Along shot, but have you checked the crankcase breather hose and vent? i had a P0420 code and that is what it was. Once replaced, code cleared. It maybe you have a small hole in it.

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13 hours ago, Mark s-Type said:

Hi with that code and what you have  what done. Along shot, but have you checked the crankcase breather hose and vent? i had a P0420 code and that is what it was. Once replaced, code cleared. It maybe you have a small hole in it.

Thank you.

Hopefully now sorted. Took readings from both Lambda Sensors on my diagnostics and the graph views showed a major difference between up and down stream sensors. Swopped the upstream (NEW) sensor for the old removed one and the graph readings came in line. Have since done some 400 miles without any codes showing. Fingers crossed.

I will keep the crankcase breather in mind for the future. However, it would seem odd to me that there was a problem on the breather as I would expect that to have an affect on both Engine Banks, not just Bank 1.

Many thanks and Regards, John

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1 hour ago, Mark s-Type said:

Hi John as you say both banks would have the problem that did happen, but it started with just the one bank, this did not last long before both banks showed up.

Mark

Fortunately my problem was/is restricted to Bank 1. Every thing is still working well at the moment, having done some 500 miles now with no re-occurrence.  Fingers well and truly crossed.

 

Best Wishes and Regards, John

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