Catalytic Converter Failing? Need Assistance with Data

Need some of the Prius Chat experts to look over the freeze frame data to see if I’m indeed having a catalytic converter failure.

History – After scanning the Prius Chat forum concerning battery module replacement I decided to buy an 05 Prius at an auction that had a known HV battery failure. (Special thanks to ryousideways for his very in-depth thread on battery module replacement with inputs from jdenenburg and others). I replaced three bad modules and balanced the battery as instructed and the battery is performing wonderfully. Once the car was running, I replaced the MAF sensor and one fuel injector based on codes that were generated.

The car runs great now, but I keep getting a P0420 “Catalyst System Efficiency Below Threshold Bank 1” code that will pop up anywhere 25 to 350 miles after I reset it. I have recorded the freeze frame data in the attached file.

I used some fuel additive in the first tank of gas to make sure any water that might be in the fuel wouldn't cause a problem (I don't know how long the car sat). I also ran some 93 octane, some non-ethanol 87 octane and then regular 87 octane (10% ethanol - hard to find non-ethanol gas around here) and recorded the freeze frame data each time the code appeared.

I wanted to make sure the code wasn't due to another sensor before replacing the cat.

Anything stand out in the data that would point to something else?

Thanks for your time.
Ken

 

It's got 160,000 miles but doesn't seem to burn any oil. Compression checks on the cylinders were all good.

The front Air-Fuel sensor and the after O2 sensor seem to respond very quickly like they are functioning properly base on the live data from the scan tool. I've heard that when they start to go bad, they become sluggish. However, the after O2 sensor seems to read between 0.7 -0.9 most of the time. I don't know if that's normal.

I'll check out the YouTube videos on scrubbing the CATs to see if that will help.
If scrubbing the CAT doesn't fix it, I'll try replacing the after O2 sensor.

Wouldn't the P0420 code be thrown shortly after resetting it every time if the CAT was bad, rather than waiting 350 miles? I'm not sure what else the ECU looks for to generate the code besides the AF sensor and the O2 sensor.

One other thing I've noticed in the data, sometime the barometric pressure is down to 12 psi. Is that normal?

Thanks,
Ken

 

The long term fuel trim was reading around 20 when I had the misfire so I assume it was running rich. The code reader is a Harbor Freight scan tool. A Toyota tech tool would be really nice but for my weekend garage, Harbor Freight will have to do.
What would normal Cat temperatures be?
I do notice that the average fuel mileage is increasing with each tank of gas. It started out at about 40 mpg. The next tank was 41, then 42, etc. It's now just over 45. I'm hoping that the Cat is fixing itself, either that or I'm getting better at driving a hybrid. I've got 3000 miles on it so far and most of my commute is around 65mph. Don't know if that's reasonable for an 05 model.

 

Ahh, if that's the case, I'll watch the temperature spread to see if it gets closer over time.

As far as the MPG, that's average per tank. I've run about 7 tanks of fuel through the car and each one seem to be getting a little better fuel mileage.

 

Thanks. From the scanned live data, I believe that the rear O2 sensor is not varying much. It seems to go between .7 to .9 most of the time which seems inline with the above. I've got an Air-Fuel sensor up front and it seems to go from 3.2 to 3.4 most of the time. I'll have to check and see if the scanner can download data to graph. Since it doesn't have an O2 sensor up front, I don't have that data to compare.

 

Right. The O2B1s1 is the Air-Fuel Sensor. It's readout is always around 3.3 whereas the O2 sensor is usually between 0.1 and 0.9. The scanner apparently doesn't designate the difference with the label. I'm not sure what year Toyota replaced the front O2 with the AF sensor but it's apparently on the Gen IIs.