Cheap Catalytic Convertor getting P0420 same gas mileage

Always curious if low cost O2 sensors work... So it a more expensive one fixes it, we'd like to know?

 

Cheap O2 sensor is first suspect. Get OEM and return the old one

 

IF any sensor or part functions as the ECM expects (is programmed to allow), then it "works". It's just that the collective experience shows that cheap parts often don't meet that standard.

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What you do is your choice. You could:

- check the repair for any exhaust leaks (even tiny leaks can throw off the cat test. Unless you used an OE gasket at the spring bolt joint then that commonly leaks)

- replace the sensor with a "genuine" Denso or Toyota(denso) unit

- replace the cat again

- look at scan data to see what the sensor is doing

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But sometimes you can't beat cheap...

 

Benjamin Franklin supposedly once said, The best solution is the cheapest, but the reverse is not necessarily the case.

 

so sad! I'm facing the same issue like you right now. I used the Bosch sensor (should be a ok sensor right?) with an extension, and even tried the Cataclean too. nothing seems working to turn off the engine light so far. any more idea guys? I've already spent $400, do I really need to spend $1000 more?

 

Yes, you can throw parts at the problem and cross your fingers (like an O2 sensor you have no idea if it's the problem or not) or you can collect some data with a BT adapter and a phone app to monitor while running/driving to tell you the story. I think blindly throwing parts at a problem is usually not very cost effective. If you gather the data there are many here that can help you interpret the data even if it's Greek to you.

I'd rather see you invest in an OBDII BT adapter and a phone app so you fix the actual problem. Having a way to diagnose your car will pay you back huge if you keep the car a while. An older Prius will certainly have some problems going forward that you will be in a position to quickly diagnose. Data is the holy grail with a complicated car like a Prius.

BTW, a bad cat or rear O2 will generally not affect fuel economy since it's not used as an engine control sensor. It's only purpose is to monitor the effectiveness of the cat. The exception would be a really clogged cat, which would affect A/F ratio as well as engine temp. Since you don't seem to have those problems you can rule that out I think.

 

Nobody knows since you have no codes or data to shed some light on the issue. If you have nothing to go on I guess the only way forward is to cheat, which is cheap and easy, but it would be much better to diagnose the problem and fix it. If you can collect data from Engine RPM, Vehicle speed, A/F sensor, and rear O2 sensor we can probably make sense of this pretty quick. If you collect data you need to collect all data items at the same time and turn off data by frame and use asynchronous data collection so you're not looking at aliased and time corrected data. Preferably start data collection from a cold start on the car and include both city driving and highway data with no stops. About 15 minutes of driving should be enough.

 

You already have a good start with the BT adapter. Everyone has an app they prefer, I like OBD Fusion for data collection and general drive time monitoring. There are YT videos to follow for setup and use of data logging. You can view the data you collect on the app, export a CSV file to Excel to graph it, or use Datazap.me to upload the raw CSV file and let the website do the magic of displaying in graph form for you if you're not comfortable doing that in Excel.

There is really no reason to suspect an O2 sensor until you see it in action while driving. Even a cheap O2 may be working just fine. You won't know until you can evaluate whether it's working correctly or not. If the O2 sensor shows it's working properly and you also check the A/F ratio sensor to check engine running condition, you are most likely looking at a degraded cat. This is likely if you burn a fair amount of oil and an inexpensive cat will degrade much faster than a high quality (more precious metals) cat.

Not every OBDII BT adapter can collect data fast enough for an O2 sensor. I use a Veepeak OBDcheck BLE+ and it works well for me on both IOS and Android and I don't see any aliasing from too slow data capture. It's $42 on Amazon and was a high recommendation from Dr Prius for his app. There are other good ones too, but that's what I used to find my P0420 problem and solved it. Good luck and feel free to ask questions.

 

that was a quality informative post, now i want to collect and post data and i dont even have an issue, and i have a cheap cat and cheap 02 sensor for a stolen cat, but they are new lol

 

NEW = never ever worked



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well, they worked fine so far, almost 60 miles and two days

 

It really depends on what you are looking for. Decide that first so you get exactly what you need at minimum. In this case I'm thinking P0420 is the target for testing. So I wouldn't record Mass AF sensor or O2 sensor equivalency ratio (Torque doesn't list the unit but judging by the range they show that would be Lambda). I do like LTFT and STFT is nice if you have no problems capturing data. The LTFT is the end product of many sensors that's part of the A/F ratio control system so by itself if it's within spec we really don't need to see more data about that right now. If your LTFT is 5 or below your engine is running pretty efficiently and we can discount that as a reason for the P0420. Acceptable spec is 10 or below according to Toyota. For the O2 Bank1 sensor1 we need raw voltage so we can compare with the O2 Bank1 Sensor2. This critical for evaluation and diagnosis. The difference we see between the 2 O2 sensors generally tells the story. If the B1S2 very closely mimics B1S1 that will tell you the cat can't clean the exhaust. There exceptions to this when the engine is not running within spec or there are lots of misfires, so we need the other data just to verify nothing like that happened during the data collection period. A calculated value from the raw voltage like Lambda doesn't give anything we don't already see with LTFT.

Please add Vehicle speed, Engine RPM, O2 Sensor bank1 sensor2, and coolant temp might be nice because nothing counts for emissions until the vehicle gets warmed up so we can disregard any reading before that point. Coolant temp isn't really needed, but nice to have if you can sustain the data rate so we can see when warmup completes, although we can see that with other data were collecting also. Because the Prius is just plain weird starting and stopping the engine at strange times engine RPM is kind of important to see on a graph so we know the engine stopped and that's why the O2 sensors went to zero or close to that and we can ignore that portion of data. Vehicle speed and RPM also tell us if you are accelerating hard so we can monitor that portion of exhaust gas reaction in the O2 sensors. It sounds complicated but it's really just common sense after you look at a few data logs and data relationships you can clearly see what's going on.

I like to capture data at 2 samples/sec... so that would probably list as 0.5sec sample rate. That's fast enough for the O2 sensors with no aliasing (you can get by with 1 sample/sec if you need to) and the more reasonable we keep the sample rate the more data channels we can record at a time with out the BT connection getting overwhelmed. BT can only transfer so much data/sec and the little processor inside the adapter can only prepare and send so much data/sec. Every BT device will be a bit different in that regard so trial and error.