My 06 S/C currently has 154000 ish miles on it....
It has started throwing up an occasional Engine Warning Light and when scanned the codes are
P0420 & P0430 which are catalyst system below efficiency threshold, 1 code for each bank of the engine.
The car shows no symptoms whilst driving with the light on.

The curious thing is I can drive 400 miles just pottering about on my weekly commute to work, shops etc and the warnings don’t appear. Hit the motorway at motorway speeds and the warning returns but only occasionally, not on every journey, so far I’ve reset the fault twice in the last 1000 miles or so.

So the point of the post.... have my cats finally got to the end of their effective lives ? Or could it be the 2 O2 sensors failing which I find less likely.
I understand the exhaust system will run hotter whilst on the motorway due to higher sustained engine speed.
Searching the forums doesn’t reveal a great of discussion on this subject.

Any thoughts out there in the hive mind ??

Click image to enlarge

Click image to enlarge

I had a similar issue in my 07 4.2 SC at about 20,000 Miles less than you, after a backfire when I ran out of petrol, with 50 miles Range still showing!

Absolutely no symptoms other than the intermittent engine management light.

I also took her to a catalyst replacement garage who confirmed that the catalysts were at the end of their life. I think the backfire effectively accelerated the process and finished them off.

I had two choices as I saw it, either keep clearing the fault about once a month - which I did for a while, however the light would come on part way into a long motorway journey and the fuel usage would soar.

Or, replace the catalysts, which I did after searching for some reasonably priced catalysts online. I managed to have both catalysts replaced with OEM parts for less than the cost of buying one from LR.

I also had to replace one sensor, there are four, about a month after the catalysts.

Hope this helps.

Absolutely spot on 👍🏻
Could you PM the supplier of your replacement cars please ? Current: Supercharged 06 FFRR in Java Black
Previous: BMW 740D M Sport
Previous Previous: BMW 730D Sport

PM sent

Hi all don’t suppose either of you could pm who you used for the cats? Current stable:
2006 BMW M6
2007 4.2 V8 S/C FF
Gone:
2002 4.4 V8 FF