CODE : P0420. Bank 1 Efficiency Below Threshold.

[Wrinkly]

Used my car for the first time in around five days yesterday. Before we start going down the track of S Types and batteries with low power, my battery is a 95Amp/Hr and is less than 12 months old. It spends regular times connected to my CTEK MXS 7.0, and had been connected for three days before being used yesterday. 

During the course of yesterdays journey a yellow engine warning light appeared. Stopped and checked the code which was P0420 as above in "Title". Erased and reset and then completed a journey of some 65 miles. No further code regenerated. 

On 13.11.2021@ 63832 miles new Lambda Sensors (Upstream and Downstream) were fitted along with a new Catalytic Converter. This was done after a lot of investigation Including smoke tests etc etc., and questioning about this code keeping reappearing after being reset. It would reappear after some 18 - 20 miles of use and happened many times. It has to be said that the Catalytic Converter was well and truly killed, as was eventually discovered and was subject of many posts on this Forum before being rectified.

The reappearance of this code yesterday was after some 800 miles of the new parts being fitted. If it was as previous experience, the code should have reappeared after some 18 - 20 miles but it did not and has not. Codes checked again this morning and nothing listed.

My question is simply, "Can someone explain this freak one off appearance of P0420 yesterday." The car is running perfectly and I am not at all concerned, I would just like to understand what, why, how this has happened. 

Many thanks for your attention in reading this submission and for any forthcoming explanations etc etc.

Best Wishes and Regards, John. 

Edited January 29, 2022 by Wrinkly
grammar

[Wrinkly]

On 1/29/2022 at 12:49 PM, Wrinkly said:

Used my car for the first time in around five days yesterday. Before we start going down the track of S Types and batteries with low power, my battery is a 95Amp/Hr and is less than 12 months old. It spends regular times connected to my CTEK MXS 7.0, and had been connected for three days before being used yesterday. 

During the course of yesterdays journey a yellow engine warning light appeared. Stopped and checked the code which was P0420 as above in "Title". Erased and reset and then completed a journey of some 65 miles. No further code regenerated. 

On 13.11.2021@ 63832 miles new Lambda Sensors (Upstream and Downstream) were fitted along with a new Catalytic Converter. This was done after a lot of investigation Including smoke tests etc etc., and questioning about this code keeping reappearing after being reset. It would reappear after some 18 - 20 miles of use and happened many times. It has to be said that the Catalytic Converter was well and truly killed, as was eventually discovered and was subject of many posts on this Forum before being rectified.

The reappearance of this code yesterday was after some 800 miles of the new parts being fitted. If it was as previous experience, the code should have reappeared after some 18 - 20 miles but it did not and has not. Codes checked again this morning and nothing listed.

My question is simply, "Can someone explain this freak one off appearance of P0420 yesterday." The car is running perfectly and I am not at all concerned, I would just like to understand what, why, how this has happened. 

Many thanks for your attention in reading this submission and for any forthcoming explanations etc etc.

Best Wishes and Regards, John. 

Anyone any ideas?????

Cheers, John