Non-fouler trick - both downstream sensors on CA emissions? 2007 Mazda3

[jonnymopar]

I was getting P0421 on my 2007. The car has a ton of miles and I'm sure the catalytic converter has lost some efficiency by now. I put a single drilled-out non fouler on the 2nd O2 sensor and the code went away. Now I'm fighting with a P2096 that won't quit. I replaced the 3rd sensor and that didn't do it. Wiring checked OK from the PCM to the connector. I logged a short drive in FORScan and the sensor is working fine. Anybody that's done this with a CA emissions car: did you put non foulers on both the 2nd and 3rd sensor?

 

[concept]

I found this info:

The P2096 code in a Mazda vehicle indicates that the post-catalyst system fuel trim is too lean on bank 11. This means that the air/fuel ratio is higher than the specified target, indicating a lean fuel/air mixture coming downstream from the catalytic converter of the vehicle1. This mixture is read by the oxygen sensor and transferred to the powertrain control module (PCM)1.

This code can be triggered by issues restricting the flow of fuel, such as failing fuel pumps, clogged filters, and damaged fuel pressure regulators2. If the P2096 code is accompanied by a code like P0420, the catalytic converter is a likely culprit2.

In some cases, this issue might be caused by improper control logic of the PCM3. For instance, some 2010 Mazda 3 vehicles with a 2.0L (LF) engine or Mazda5 vehicles with a 2.3L (L3) engine may experience the MIL on with DTC P2096:00 (Target A/F feedback system too lean)3.

It’s important to note that this is a generic OBD II code, which means it has the same meaning for all Mazda vehicles as it would for any other vehicle45. If your vehicle is running too lean (too much air for the amount of fuel present), you may notice symptoms such as a rough running engine, knocking, red catalytic converter, bad fuel mileage, and a check engine light4.

 

[negusm]

Good chance you have a vacuum leak letting in too much air. Do the old vacuum leak test trick to see. 15-20 years is about when all the rubber hoses in an engine bay get rock hard and form cracks\leaks. Otherwise check all things related to air intake.

If still nothing then I would move to a fuel pressure test.