P0420 code and non-fouler trick tip~ Steel Wool
2004 ZTS with the 2.3 engine. I got the P0420 CEL code recently. Car runs great with no issues at idle or speed. I viewed the rear O2 sensor voltage with my Actron scan tool and the rear voltage was all over the place hence the CEL light. I use two (2) non- foulers to space the rear O2 sensor out of the exhaust flow. I put it back together and cleared the code with my fingers crossed.
No-go. Check engine light came on in a few days. Checked the voltage graph and although not as wild a shift it must be enough to trigger the code.
I ordered a Motorcraft rear sensor from rock-auto with the intention of replacing it. The sensor arrived and it was after I removed the non-foulers and sensor I discovered that the one they sent me would not fit. The plastic plug was keyed differently and it would not plug in. Crap.
While I had it off I decided to do the "steel wool" trick that was mentioned in several forums. I left the O2 sensor screwed into the non-foulers and packed steel wool into the open end (opposite the O2 sensor). I packed it firmly but not excessively. Put the sensor back into the vehicle and cleared the codes.
Its been about a week and no codes have been thrown and non pending in the scan tool / vehicle computer.
If you are going to do the non-fouler trick I would highly suggest packing steel wool into the end the 1st time you have it off. I am returning the O2 sensor to rockauto. This car has 144,000 miles on it and has been trouble free minus the #3 coil pack I just replaced. I also put new struts on it.
My 2003 has 190,000 miles in the 2.0 liter Ztrec with original O2 sensors.