Lavrishevo

iTrader: (1)

So I'm back with my 02 codes again. Well, this time it's p0430 bank 2. Ridiculous.

I replaced my cats with high flow Magnaflows and everything was fine for about 15000 miles. Checked and checked for any kind of exhaust leak. None to be found. Had the muffler shop hook up their diagnostic scanner to actually read the values from both the front and rear 02 sensors on both bank 1 and bank 2 real time and they are reading within very close values to each other. Nothing is out of order on the scanner. I know in the reference guides it says to use an oscilloscope to test the sensor but I don't know who would have one here in PR and know how to do this.

My last problem was p0420 and I replaced the cats as mentioned above and no more codes for quite some time. I was doing some searching and I found one article that mentioned how aftermarket cats can cause the catalyst efficiency code to come back after some months, on the LS 400. I am really wanting to put rear 02 eliminators on there and just say to hell with it. Any other ideas? I guess it could possibly be a kink in the wire but it makes me wonder as it's bank 2 when it was originally bank 1. ugghhhh.

3UZFTE

Obviously without diagnosing it myself, I am just shooting from the hip. You had a p0420 (Bank 1 catalyst below efficiency), and replaced both cats with aftermarket units, and it solved the problem for some time. Now you have a p0430 (Bank 2 catalyst below efficiency), and took it to a shop and had them diagnose the problem. What they came up with that the sensors are reading very similar... Did they give you the diagnoses that your cats are bad?

Now, for the theory...... As a technician, I always recommend replacing cats with OE replacements. Although they might cost more upfront, you know they were specifically designed for your vehicle. A cat works by having precious metals inside the cat react with excess fuel, causing it to burn hot, and burn off any excess fuel reducing tailpipe emissions. The reason why they cost more (usually) is because since Platinum is going for $1,450 per troy oz., and palladium is going for $650 per troy oz., which are the two important precious metals inside. The more of the precious metals, the better the catalyst will respond and reduce the emissions, and extend the amount of service life. The cheaper the cat, the less precious metals are inside (that's just business), the harder the catalyst will have to work, possibly shortening the life if it's working overtime constantly. I am not going to say Magnaflow doesn't make great products, they do, they just don't make a specific fit, but a universal one, and being a cheaper product on the market, you have to wonder how much precious metal are in those cats, (possibly very little) to be able to keep up with a poorly performing engine....

Now for practicality... You had the cats replaced because of a bank 1, did they actually need to be replaced or were they OK, and you had other problems creating your p0420. Now the cats have been replaced with non-OE cats, you could have masked the problem for a short period of time with new cats, but essentially your back at square one. Now they have done a bit of diagnosing, and say you have to replace your cats again....

You can either....
1. Replace the cats, again, either with OE replacements or aftermarkets and test your luck.
2. Continue to diagnose the vehicle to find out if there is a deeper issue. (Exhaust leak, dirty combustion, faulty O2 sensors.)
3. Try to work around this whole thing and just ignore it, or try to blindfold the system with O2 simulators.

Hope this helps.

Lavrishevo

iTrader: (1)

Thanks 3UZFTE, that is very good advice. You know, one thing I noticed but did not really know at the time, was that the post cat bank 02 sensor was taking longer to match the values compared to bank 1's. Not being an expert, I really had no clue the timing involved and when the tech was looking at the real time readings I noticed how this sensor was slower then the other. I was able to speak to a knowledgeable tech at a Lexus dealer and he mentioned that "lazy" 02 sensor's can cause the code. He also said that if the cats were causing the problems then I should be getting both 420 and 430. I have also spoken with Magnaflow as well as calling around to various dealerships. It definitely was the standard answer from Lexus that aftermarket cats are notorious for causing codes to comes back but Magnaflow did say that I should be fine with the model of cats I put on.

My plan of action is to replace that one 02 sensor and see how she acts. If it comes back I guess I will save for OE cats or do the simulators. I know it does go into a limp or preset mode with the code and power / fuel economy is reduced.

This is the info I got back from the tuning shop that sells the simulators:

3UZFTE

Sounds good.... One thing I would like to add about the O2 sensors.... The upstream O2 will first sense the oxygen levels in the A/F mixture and will cause voltage to go up or down depending on lean or rich mixture, that same air will flow through the cat, than to the downstream O2. So there should be a slight delay between the 2 sensors. If the upstream goes up and the downstream does at the same time, you can likely speculate there is an issue with the cat. The delay is somewhat normal as it takes an additional second for the air to flow to the downstream sensor. Another good way to tell is lets say the upstream goes up to 4.5v, and the rear goes up to 4.5v, you can also speculate that the cat is not providing enough of a catalyst burning off any excess fuel that is in the system. So.... Theoretically, the upstream should be go lean-rich-lean-rich on a wider scale and the downstream should be slightly behind/delayed, but also goes lean-rich-lean-rich, but on a smaller and more narrower scale because the catalyst is burning off any excess fuel, reducing the rich condition.

Not sure if it helps at all, but I would do like you said, try replacing the rear O2 sensor(s) if you are just going to shot gun as this is probably the easiest and cheapest part. Rarely have I ever seen an upstream O2 cause a catalyst inefficiency code.

Good luck.

Lavrishevo

iTrader: (1)

That is fantastic information. Honestly, this kind of way of diagnosing the 02 sensors and the cats that nobody mentions. When I was looking at their scanner it was showing both down stream's or both up streams. It seemed like I was not able to see all 4 readings at the same time. What it seemed like to me was that the bank 2's post cat was not keeping in line with bank 1's It would hit voltage levels that were different then settle in at almost the same.

Another couple of question if you don't mind. Do you know the ranges that these sensors should be fluctuating given the cat and fuel intake system are doing their job? Also, how do you tell if the cat went bad?

3UZFTE

That's pretty typical that only 2 "PIDS" (sensors) can be viewed, usually the more expensive or newer the scan tool, the more pids or things you can monitor. If you can, try to diagnose one bank at a time. You do not really need to compare bank 1 and 2, but you need to compare the two once you've come up with a bit of a diagnoses to be able to prove if it's normal or not.

O2 sensors feed the computer a 5 volt reference signal. IIRC, 5v means that there is 100% oxygen in the exhaust/O2 sensor, and 0v means that it is 100% fuel. The computer has a pretty good idea that if it sees the engine running, and voltage is pinned at either 0v or 5v, it knows that that's an impossibility and usually will through a code. Once the computer goes into closed loop, a perfectly running engine will likely send a rich signal to the ECU, as the rich A/F mixture flows through the upstream O2, the computer will adjust and command a lean signal. As the rich mixture continues to flow through the cats, than to the downstream O2, it will monitor the downstream O2 to see if the catalyst is working within limits. Not long behind is the lean mixture, as the lean mixture hits the upstream O2, the computer will sense that, and command a rich signal. So theoretically, if the system is operating correctly, it should look something similar to this. The reason why it dips at 38 seconds is that the driver stepped on the gas, causing the mixture to change and read rich, but than as the throttle is eased you can see the readings come back in range.



Let's focus on the Bank 1 (Red B1S1& Blue B1S2). In the above picture, you can see a pretty normal reading for O2 sensors. If you look at the red line, it will go from Rich (near 5v) to Lean (near 0v) back to rich, and so on, this is perfectly normal. Now look at the downstream, or sensor 2, it follows the upstream, or sensor 1, but within a much smaller scale as the catalyst is removing any excess fuel.



Here you will notice the note that says inefficient catalyst. It isn't live data, but you can see both sensors are reading, but they are reading the same. It is likely sense the O2 is providing a pretty good reading, rather than just pegging at 5v or 0v, you can bet the problem is not with the sensor, but with the catalyst.



Here is an efficient catalyst, you can see it's similar to the live data in the first picture.

I'm glad to answer any questions you might have being that no one else is stepping up, feel free to keep them coming if you got any more. Again, hope this helps.