So I replaced my downpipes and exhaust a few months back (Nameless/Mina) and after around 500 miles or so I had P0420 and P0430 Catalyst System Efficiency Below Threshold Bank 1 and 2 errors pop up.

The car also started stuttering when you initially take off or when you hit it hard at speed. I cleared the codes and they haven;t popped back up but the stuttering is still there. The codes haven't popped back up after putting some miles on.

I took it into the local indy Jag shop and they couldn't find the cause and sent me to the local dealer. I am about to take it in. I was thinking the O2 sensors may have gone bad. However, the Indy shop is thinking it is a transmission issue.

Anyone have any insight before I take this over to the dealer?

 

o2 sensors would throw a code it bad!

 

You could try watching OBD live data - very cheap & easy to do - hoping for clues.

 

You might consider a fluid change for the transmission. I have a 2006 XKR with 42K and it would shudder a little when cold. I just did the change with Mercon SP and the shudder has completely gone. You know the transmission sealed till death. I don't know if a dealer will do that for you. Follow Sam's instructions, it's not that hard to do and on a hoist it is quite simple.

Good Luck
Bob

 

Did you do a hard reset on your car after you changed your exhaust system?

 

I did a hard reset but it didn't help. The local dealer wants to charge me $2,000 to replace the O2 sensors. I will be tackling on my own.

 

If you are doing the upstream o2's those are simple, I hear the read ones are worse.

 

Use only O2s that have the pigtail already wired and compatible for your car, the generic ones you cut and modify to length have been problematic in this forum, the o2s are inductive sensitive.

Read some of the threads on replacement, I believe there's a way to get the passenger lower from the inside (really) through a plug in the firewall. Cut the leads and use a regular socket to remove, then use the o2 socket to install.