I have P0420 on my 06 prius with 220K miles. I reset it and it comes back after roughly 50 miles-ish. I have freeze frame data when the code is thrown. I read live data at 2500 rpm while the car is warm, and have all the data on the video link below. My upstream O2 voltage is 3.1-3.3V. Downstream is .2-.4V. I understand that the downstream should be steady, and the upstream should fluctuate and read something between .1V-1V. I have also taken thermal temp gauge and measured across both cats and readings downstream seem to be only slightly higher (+50F). It should be ALOT higher shouldn't it? Why is my upstream voltage so high? What does it mean if downstream fluctuates? I want to verify cat is bad before going that route and regretting it. Live Data Video: Dropbox - P0420 - Live data.mp4 Diagnosing P0420 by Bryan Holloway posted Jun 23, 2016 at 10:48 AM
Upstream is higher than the conventional #, but I don't know if a Primus adheres to the common convention. A fluctuating downstream is indicative of poor cat performance. Since they tend to be inexpensive, I recommend you replace the downstream with a bosch or denso OE style sensor. If that doesn't change things, almost certainly the cat.
Are you familiar with testing individual O2 sensors by resistance? Im wondering if i have a bigger issue like a very rich mixture that has caused the cat to die. That might explain the high voltage reading on the upstream sensor. It burns a little bit of oil so I guess it could be that too.
So I tried a couple of things since OP. I cleaned the cat in a oxalic/citric acid solution at 60-70C for 12 hours. The light still comes back and my downstream O2 reading jumps from .15-.8 constantly. It seemed to be jumping at a smaller range before I cleaned the cat. Also I noticed I am able to look at the "Readiness codes" on the programmer. It gave me one false code, a P0441 (Evaporative Emission Control (EVAP) System Incorrect Purge Flow), P2501, and a P0803 (1-4 Upshift Skip Shift Solenoid Control Circuit Malfunction). Is it possible the EVAP might have something to do with this?
You should reset your battery or erase all the codes after the cleaning of the cat. What amount of the acids did you use and how much water did you mix it with? How did you keep the water that temperature for 12 hours?
Which battery, Hybrid batteries or the 12v? .1 moles of oxalic and .1 moles of citric. I used Savogran 10501 Wood Bleach (dihydrate), for the oxalic acid part and Ball Citric Acid (For canning). I used 12.6g of oxalic acid to get that at 0.1 moles/L and 19.2g of citric acid to get that at 0.1 moles/L. That worked out to 48g of oxalic acid, 73g citric acid and 1 gallon of water for 1 gallon of solution. I had some heat lamps I put on it and measured with a digital thermocouple and an infrared thermometer to make sure I was at 60-70C.
You would disconnect the 12v battery to reset the lights. Disconnecting the hybrid battery momentarily never does anything to the car. How many gallons did you end up making?
Oh so resetting the ecm through the programmer would do the same thing then, and I already reset it and it came back. I made one gallon. Enough to fill up to the o2 hole with the inlet of the exhaust blocked off
The last person that did this mixture and posted made around 6 gallons of this stuff and soaked it for 6 hours. I'm not sure how you were able to get away with making only 1 gallon and soaked the entire cat. Maybe you have to make more solution and let it actually rinse out the contaminants. His was only successful for about 3000 miles before the light came back on. But he didn't have the right temperature water for the 6 hours.
Maybe he filled the entire exhaust with the solution. I filled it from the first cat, to the downstream O2, which takes less than a gallon and completely covers the cat.
he soaked the cat in the solution. He did not pour the solution into the cat I think it's important to have enough solution to dilute and rinse out the contaminants in the cat while you agitate it.
Can you say more about what kind of gauge you used for this, and how you used it? I ask because I once saw a youtube vid where somebody showed using an IR temp gun with a laser guide spot, and was clearly just putting the laser spot down through a narrow gap between heat shields and thought he was measuring cat temperature that way. The only thing that video was showing was that somebody had apparently never opened the manual for his IR temp gun, or wondered what the distance:spotsize chart on the side of his gun was for. Spoiler: you can't do it that way. -Chap
I plugged the inlet side of the exhaust, stood it up, and filled it from the O2 hole until it was full. I then soaked it for 12 hours at 60-70C. It took less then a gallon. I agitated every 2-3 hours.
You might have to repeat the process.....with more fluid. The way you did it, all the contaminants that was removed had no place to go. Also all the contaminants mixed with your acid bath probably changed the formula significantly because you had so little fluid to work with.
Interesting point. Ill look into that thanks. What about those codes in the above post I was asking about?
Upstream voltage is "high" because it is a "Wide Band" 02 sensor, the set voltage differ greatly from one OEM to another and in some cases even from one sensor brand to another; but normal is ~2.5V (2.0v - 3.0v) and varies during operation slightly. Modern ECU's use the "wide band" Heated Exhaust Gas Oxygen (HEGO) sensor types to more accurately monitor and therefore control Air-Fuel Ratio (AFR), providing better engine life, economy and performance. The second O2 sensor is a run-of-the-mill "Narrow Band" sensor and it's just there for emissions verification as you discovered with your "Catalyst Efficiency" DTC. Subaru, Honda and from what I am learning Toyota have VERY tight limits on Catalytic Converter performance and will set a DTC even when the system is controlling emissions to WELL within mandated limits. Unfortunately, I am not familiar enough with these issues on a Prius to provide any solutions, except that an exhaust leak upstream of the catalytic converter can cause the DTC you have, as well as a worn oxygen sensor or cat converter.
