Error: Catalyst System Efficiency Below Threshold
Caused by Rear O2 Sensor, one after the catalytic converter (now test pipe), on the intermediate pipe.

So, how to Prevent CEL P0420 AND run a test pipe? Before we can have a successful solution to this, I have a Million Dollar Question:
Does the ECU adjust fuel based on rear O2 sensor data? Or the ECU merely uses this O2 sensor data for catalytic convertor efficiency?

According to Haynes Manual
If you take a reading at the rear o2 sensors on a car WITHOUT catalytic converter in place, the reading fluctuates between .1 and .99 volts. It should be an identical reading to the front O2 sensors at this time, as there is not cat to clean up the exhaust. This throws P0420 code.

If you take a reading of a rear o2 sensor with the stock cat in place, it fluctuates between .1 and .45 volts, keeping the reading under the .45 volt threshold. This makes perfect sense, as the cat are properly doing their job. No error codes!

-- If ECU fine tunes the fuel delivery based on rear O2 sensor data --
We need to add some resistence into the wires coming out from the O2 sensor, or some kind of artificial O2 sensor which will trick the ECU and keep the voltage constant at 0.45.
Found some "MIL Eliminator" for Fords & Subarus: http://www.ponyexpressperformance.com/
Will this work for Maxima...OBD-II compliant ECU?

-- ECU does not alter engine performance because of P0420 --
We need to get rid of the annoying CEL light. A black tape on the gauge cluster would work.
Eventually, this will fry the rear O2 sensor and render it useless, however, your performance will not be affected.


Any ideas?

 

I have a curcuit fault and cant find it... So i just took out the bulb the CEL uses I win...

 

just keep re-setting it til it doesn't come back on again

 

That didnt work for me...