2005 SWAP UPSTREAM O2 SENSOR- Rid Code P0420 Catalyst System Efficiency Below Threshold (Bank 1)

Recently I received a DTC code P0420 prompting me from my CEL. The live feed data from my OB2 code reader revealed a consistent “0” on upstream O2 sensor, while downstream was noting 3-5.0 over minor throttle while I was parked in my garage. I assessed it as a BAD UPSTREAM O2 sensor. Also, helpful towards my deduction was that I just replaced the catalytic converter to my 2005 Prius a few months back. I scored a $4 used piece from a scrapped Prius at my local junkyard and went to work.

1. JACK UP CAR.

2. DESIGN, UPSTREAM O2 SENSOR. You will notice immediately that the sensor has a unique cap to it that adds to shield and help cool the O2 sensor. I decided to cut at it with a dremmel tool, vice order a special removal tool.

3. FROM BELOW, REMOVE UPSTREAM O2 SENSOR. Removed 2x screws to a small heat shield, providing me access to dremmel-cut away at the O2 sensor.

4. RE-ATTEMPT ACCESS, FROM ABOVE. I didn’t have enough O2 sensor access, so I had to try again and come from above. I dropped the vehicle off the jacks and tried from above. I removed the above heat shield and cut at the O2 sensor from above. That worked nice.

5. 22MM CRECENT OVER O2 SENSOR SOCKETS. For breaking the O2 seal, my purchased specialized O2 sensor sockets were less helpful than a HUGE 22mm crescent wrench. This was a frustrating venture that required an overall ~ 6 hours of frustration to include an overnight cool down for reflection.

6. ALUMINUM NOT COPPER ANTI-SEIZE. I couldn't find any copper anti-seize from any local auto part shops, so I went with what I had: Permatex Aluminum Anti-Seize. The initial testing at idle in my garage, produced a heavy amount of smoking and burning that quickly went away with time. Copper based formulas are limited to 1,800 degrees F and aluminum based formulas to 1,600 degrees F.

7. ROAD TEST. I cleared the CEL & DTC code via Techstream computer. After a road test of 200 miles later, i still have no problematic issues & CEL didn't reappear. I also had the OB2 reader running live feeds reflected during the road test drive: upstream “0.1-0.7”; downstream “1.0-3.5”.

 

UPDATE... prior to CEL light to this problem arising, my MPG dipped down to ~34MPG. Now after upstream O2 sensor swapout: 44 MPG.