A few weeks back I posted a thread concerning Black Bess, MY03 S Type 3.0V6. I had been on a short run when the car the was drowned by an oncoming truck. Net result was Bank two spark plug wells filled with water leading to numerous misfires and potential damage to the Catalytic Converter. Long story short, replaced the plugs and coils on Bank two, having dried out the wells and gallery. This cleared the misfires but P0430 (Cat System efficiency below Threshold) then appeared. Got the Cats checked out but, according to the garage, no problem. Repeatedly cleared the P0430 and P1000 codes but on each occasion after about 15 miles they would come back. Decided it was probably a dud/damaged O2 sensor and purchased a new one for the downstream on Bank Two. Took a little time to get this done as I was not relishing rolling around on a cold concrete floor. Anyway got the job done yesterday - not the easiest exercise give the location of the sensor cables - sadly test drive today shows no success. P0430 appears after approx 15 miles.

The old O2 sensor was very obviously damaged so I was convinced I had got the the problem fixed. Short of replacing all the sensors I'm not sure what to check out / do next.

Any ideas suggestions most welcome.

Cheers in advance.

 

Sorry news for sure..

Do you have a way to monitor upstream and downstream O2's?

Catalytic converter codes are set as the correlations get similar to each other. If you have a way to bring both the sensors up in a graph the front one will cross the stoichiometric line many times and the rear should stay close to center.

 

I just had a similar 0420 code after fixing the infamous leaking coolant hose under the str blower and lean conditions on both banks. I replaced the cats (pipe and all) and new o2 sensors.

After my repairs I ran code free for several months when the P0420 code popped up. Cleared it and it came back. car ran rough too.

I took off the bank 1 cat pipe and it looked fine BUT there was a trail of black soot on the exhaust manifold mating flange so I suspected an exhaust leak. I cleaned up the pipe weld to make it flat since there was an obvious ridge on the flanged area and I reinstalled it and VIOLA! Success!

 

After putting the Jag back together (Changed S/C coupler, I got a 0420 code along with a CEL. I reset it a few times, but it would always come back after 90 -- 140 miles. The car ran fine, pulled hard, idled smooth, no issues at all except the code and the CEL. Would not pass state inspection with either of them. I ran a couple of cans of snake oil through the gas which made no difference at all. I ordered an extender off Ebay which gets the 2nd O2 sniffer out of the exhaust stream and voila, no further problems. After I reset the codes and CEL, I took a quick hundred-mile drive to get some mileage after the reset and it passed the inspection with no exceptions.

 

Im not sure I fixed it since the code comes back periodically

 

How long has it been off? Every time Ive used the extenders I get the fault code for the response time being too slow. It might have been because I was running headers and they obviously move the O2 sensors so the timing for ther test is changed.

 

I finally got to the bottom of the P0430 problem but not until after I had replaced the downstream O2 señsor and incurring a minor stroke - the latter being the cause of my tardy reply.

Ultimately it came down to needing to replace the inlet manifold and throttle body gaskets to produce the real cure. The damned things are so delicate that the backfires that can in turn result from cylinder misfires can/does damage the gaskets in a manner that is hard to discern to the naked eye.. Two years since BB was fixed and no recurrence of the problem.

Hope this helps later readers and thanks to the contributor who suggested damaged gaskets could be the root cause.

 

That sounds like the fuel trims would have been a dead giveaway!