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P0420 code and some screenshot of data logging, help
Hi CL! I have read a ton of others with the dreaded P0420 code and have replaced the gas cap (OEM new), and PCV valve for simple fixes. I have zero other codes showing up and I still get this code. I have BlueDriver app which I can see whats going on etc and took
some screenshots of the data and a video. I'm hoping it tells someone something that help point me in the right direction of what to fix next. I have take it to Lexus and they first said need to replace exhaust manifold on that side, then another tech said I needed new cats and both were over $1k to fix. They said gas cap fix was a myth. But I know it's worked for others here. So I left the shop. I want to try everything I can myself first. Being a huge DIY'er I want to do as much as I can as I have on all my other cars. I am building a motor for my 68 Camaro so I do know what I'm doing. But I can't seem to figure out if the data in these pics shows anything. Any help would be greatly appreciated.
how rapid does the O2B1S2 changes its voltage, if it is changing rapidly then its either the cat or the sensor (you can compare the rapidness with the other sensor). to rule out the sensor, you can swap that sensor with B2S2. However, I doubt it is cause. and by the way exhaust manifold has the cat attached to it, so both techs said basically the same thing. replacing it is labor intensive + Cats are very expensive
from my knowledge, i would say take it at idle, then compare with the other sensor. It wont hurt to also rev up the RPM a little and compare as well. Also it is useful to get the temp of the CAT, lots of OBD2 display that.
Basically, you dont want to see lots of fluctuation in the O2Sensor Bank1 Sensor 2 and Bank 2 Sensor 2. this is because the CAT converter should filer the burned gas and produce consistent O2 (to some extent) therefore the O2Sensor2 on both CATs should have little fluctuation in their reading. in case the CAT doesnt do its job then these sensors will see rapid fluctuation in reading because the O2 is not being as consistent as it should.
Last edited by nobelnabil; Feb 9, 2018 at 02:17 PM.
Reason: clarify
Check b1s1 to b1s2 at 2000 rpm when engine is at operating temp. If sensor 2 almost mirrors sensor 1 or it doesn't stay steady. Your cat is bad/ failing. Most times p0420, p0430 codes are always the cats
Yes, but dont depend on sensor 2 mirroring sensor 1, it is rarely the case because the CAT will be partially working so sensor 2 will be different most of the time.
Good advice given. All that activity on b1s2 (post cat o2 sensor) would lead me to believe the cat is dying, the other guys explained why. The sensor is obviously working.
I would need to see just two plots - b1s1 and b2s2. Your pcm looks at those sensors, computes a special average of how many times they switch per unit time (over some drive cycles). The closer the average is to one, the more likely to see a code. Depending on how "LEV" the car is, the exact threshold may vary. It is possible a bad sensor could create that code, but usually there would also be an 02 sensor code. I would have to see b1s1 to be sure.
One more thing I forgot to mention,it is not very common for the CAT to go bad with this car. I would highly recommend to check for exhaust leaks before considering replacing the CAT. exhaust leak will trigger that code and will also cause the O2S2 to fluctuate
One more thing I forgot to mention,it is not very common for the CAT to go bad with this car. I would highly recommend to check for exhaust leaks before considering replacing the CAT. exhaust leak will trigger that code and will also cause the O2S2 to fluctuate
Best advice yet. NEVER change a cat unless you know exactly why. I think it is actually against the law in NY. You have to diagnose it and state a reason. (If a shop does it).
Usually cats fail because of a misfire or lean condition. I have Fords with 200K, the cats usually fail because they rot out.
P0420 code and some screenshot of data logging, help
