Good morning guys, I recently replaced my CATS with higher flowing 200 cell ones from Velocity AP. It triggered the CEL and about a week after I had an ECU tune to address the CEL. I suspected that the position of the downstream Oxygen sensor (2-3 inches from CAT) was the culprit. I had the muffler shop re-locate the sensor to rear portion of the CAT. Codes went away but returned with a P2096-Post Catalyst fuel trim system too lean, Bank 1. The only changes I've made was the replacement of the CATS. I am about to replace the 2 downstream O2 sensors but I don't think that is the issue. Any ideas? I really appreciate any help/ideas

 

The code strongly suggest to me that changing the sensors won't help.

 

Can you elaborate any further?

 

How many miles have you put on it since relocating the sensor? How many since new CATs? Did you unplug the battery both times?

There is restart procedure that I only recently discovered that says you have to let the car get up to temp during initial idle so it can re-learn idle values. Then you have to go through a few drive cycles for all the other stuff.

After I installed new CATS, I cleared my codes, took a 200 mile trip and they never came back.

 

Fuel trims will not resett with clearing codes but only by battery disconnect. I would say either your rear sensors are bad, wiring or the location of the sensors is the issue . Definetly do battery disconect to restart the fuel trims
And just to be on the safe side if you did any work to your air filter or anything under the hood I would double check to make sure you don't have any vacuum leaks and everything is sealed tightly. Now I Just remembered I had one XKR here that had codes for too lean and it turned out to be rubber connector to the throttle body that was leaking vaccuum.
Also use obd2 adaptor to monitor your long term fuel trims on both banks at idle and at different loads, this will tell you if your actually running lean. When you were at my place your fuel trims were normal

 

If your codes went away without a tune to address them your lucky, I suspect your new cats are higher cell count and they function as good as factory so might be more restrictive too and maybe not, but if you have a higher flow units or no cats at all you will get a code for cats below efficiency and that must be removed in the tune. I had to remove it a more than a few xkr's

 

So I decided to take the car for a long drive, maybe the fuel trim needed to be reset or something of that sort. I drove about 200 miles, LA to San Diego and back. CEL is off and no trouble codes found per the Torque pro app. Hopefully I can lay this to rest now.

 

How do you plan on future smog checking with your new cats? And what company was willing to ship non certified cats to California?

 

I ordered the cats directly from Velocity AP. Based out of Canada. I have a smog guy... wink wink..