Lexus IS250 - P0420 - Cat efficiency below threshold bank 1

[Sponelis]

Hi all,

Couple of months ago I got an error P0420 - Catalyst System Efficiency Below Threshold Bank 1. Changed 02 sensor but that did not fix it. Two different mechanics are saying its the cat gone bad.

It is the upper cat connected to the manifold and it is impossible to find one. Anyone could suggest where to start looking for one? Can it be deleted? Any advise at this point would help as I am pretty desperate by now.

OEM part is too expensive.

[Linas.P]

What is the mileage? Cats - generally last well over 100k miles and I would not expect one to fail before at least 200k.

My first step would be to check for leaks in exhaust, as that is most common reason for P0420 - O2 sensor is measuring how much unburn O2 comes after cat, so if you have leak it would obviously show incorrectly. 

And... no - Primary cats cannot be "deleted" and it would not solve your issue anyway.

[scudney]

You probably have a small hole/leak near your 02 sensor 

[scudney]

You probably have a small hole/leak near  your O2 sensor, happened to me when I had my IS200

[Sponelis]

7 hours ago, Linas.P said:

What is the mileage? Cats - generally last well over 100k miles and I would not expect one to fail before at least 200k.

My first step would be to check for leaks in exhaust, as that is most common reason for P0420 - O2 sensor is measuring how much unburn O2 comes after cat, so if you have leak it would obviously show incorrectly. 

And... no - Primary cats cannot be "deleted" and it would not solve your issue anyway.

It’s 125k miles. I have asked my mechanic to look for leaks.

I also was getting knock sensor code P0333, and codes P0172 and P0175. Other garage told me it’s all related to the fuel mixture as cat is failing. Would these be caused by a hole in an exhaust?

Someone also suggested to install 02sensor spacer to get rid of this. I have no idea what that is, would that solve the problem?

[H3XME]

1 hour ago, Sponelis said:

 Would these be caused by a hole in an exhaust?

Someone also suggested to install 02sensor spacer to get rid of this. I have no idea what that is, would that solve the problem?

Yes it can cause a variety of issues if the O2 sensor is reading incorrectly due to the blow.

O2 sensor spacer? I presume by that they mean blanking it off, so you'll get rid of the code, but that doesn't fix the issue.. Take it to an exhaust shop and have them look for a hole and get it fixed. Should be cheaper than a new O2 sensor. Mine did the same thing a couple of weeks ago, I got bad blow coming somewhere from the under my feet, sounds like its near the secondary cats which is near the O2 sensor so I'm going to get mine fixed too. 

[Sponelis]

7 minutes ago, H3XME said:

Yes it can cause a variety of issues if the O2 sensor is reading incorrectly due to the blow.

O2 sensor spacer? I presume by that they mean blanking it off, so you'll get rid of the code, but that doesn't fix the issue.. Take it to an exhaust shop and have them look for a hole and get it fixed. Should be cheaper than a new O2 sensor. Mine did the same thing a couple of weeks ago, I got bad blow coming somewhere from the under my feet, sounds like its near the secondary cats which is near the O2 sensor so I'm going to get mine fixed too. 

My mechanic just came back to me saying he could not find a hole near 02, so it must be the cat then..

[Mr Vlad]

Lucas. An O2 sensor spacer is a spacer. What it does is enlarge the gap between the sensor head and the gubbins in the exhaust. The reason why some folk use them is it helps reduce wear on the sensor. It's meant to be illegal also I've read somewhere. I believe they use spacers for race cars.

[Linas.P]

1 hour ago, Sponelis said:

My mechanic just came back to me saying he could not find a hole near 02, so it must be the cat then..

Cat would be literally last on my list of things to check. Live data would be required to give better picture. First of all - what your lamda is reporting? When they were replaced? Generally speaking lambda sensors last ~75k, aftermarket/fake ones much less - so that is where I would start looking. If lamda is reporting incorrectly (sometimes referred as being lazy i.e. it does not trigger the code of it's own yet, but reports incorrectly enough to cause issues, rough running, misfires etc.), then you would automatically get wrong Air:Fuel Ratio and automatically will get cat performance issues, O2 sensor is just "catch-all" in the end. Only when you confident that lamda works correctly, you can expect o2 sensort to work correctly. Now just to say - it is NOT impossible that cat is bad at 125k, just rare, but 9 times out of 10 it will be either exhaust leak (anywhere between engine and o2 sensor, not necessarily right next to o2 sensor) or it will be upstream sensor giving wrong readings and messing-up A:F.

2 hours ago, Sponelis said:

I also was getting knock sensor code P0333, and codes P0172 and P0175. Other garage told me it’s all related to the fuel mixture as cat is failing. Would these be caused by a hole in an exhaust?

Yes - it would be. To simplistically explain how it works - there are 2x O2 sensors on each bank, one is "wide band" also known as "lamda" and other one is "o2" sensor. The lamda checks for remaining oxygen in the exhaust gasses, theory being if there is oxygen > then engine is running lean > then inject more fuel. O2 sensor after cat just checks that reading of lamda is correct, if it reads different level of oxygen than lamda, then there will be various codes, but the popular one is for cat performance. Usually, bad lamda gives you "too lean" code, but P0172 and P0175 are "too rich" codes, together with P0333 I would speculate maybe an issue with spark-plugs (those are 75k rated as well).

Realistically, nobody could give you definitive answer over the forum, you need life-data reading and performing several tests to find the root cause of this. Replacing cat before doing it would be "just throwing parts" at the problem, which sadly many bad mechanics likes to do "it says cat performance issue, let's replace cats" and if it turns out not to be cat, then it is customer issue...

[Sponelis]

9 minutes ago, Linas.P said:

Cat would be literally last on my list of things to check. Live data would be required to give better picture. First of all - what your lamda is reporting? When they were replaced? Generally speaking lambda sensors last ~75k, aftermarket/fake ones much less - so that is where I would start looking. If lamda is reporting incorrectly (sometimes referred as being lazy i.e. it does not trigger the code of it's own yet, but reports incorrectly enough to cause issues, rough running, misfires etc.), then you would automatically get wrong Air:Fuel Ratio and automatically will get cat performance issues, O2 sensor is just "catch-all" in the end. Only when you confident that lamda works correctly, you can expect o2 sensort to work correctly. Now just to say - it is NOT impossible that cat is bad at 125k, just rare, but 9 times out of 10 it will be either exhaust leak (anywhere between engine and o2 sensor, not necessarily right next to o2 sensor) or it will be upstream sensor giving wrong readings and messing-up A:F.

Unfortunately, I am not that knowledgeable myself to check these things. I only go by what my mechanic is telling me. When we changed the lower 02 sensor (to an aftermarket one) couple of months ago, he said that is showing wrong readings when car is idling or on low revs, but when you drive the car normally it is showing correct readings. In the other garage, the guys said that my fuel trims are -15 and should be around -4, but again this can be due to faulty lower 02 sensor or cat. So I am a bit stuck on what to do next. My original mechanic thinks that its cat and it cannot be that the new sensor is faulty, other garage thinks it could be a sensor, and the third garage just said its cat...

Car runs smoothly, no misfires, nothing. But sometime i get the other codes that i mentioned.

I am trying to take to one more garage who worked on Lexuses before, maybe they will help me there. It's just a shame that mechanics want to change the part straight away without spending enough time on the car to eliminate other possibilities..everyone is just too busy.

[Linas.P]

Aftermarket sensors are dodgy. In my experience 50% are DOA... one failing within 2 months 100% possible. Toyota sensors on internet are dodgy as well, because like 80% of them are fake. Sadly, when it comes to o2 sensor and particularly lamda sensors... you have to go OEM. I would probably look at places like rockauto.com or www.amayama.com once you know what the issue is. The lamdas are ridiculously expensive ~£175 each, the o2 are slightly better ~£80. Whenever to replace or not again - sadly live-data is required and I know very few mechanics who can make sense out of it. I guess if you have workshop manual in front of you and following the steps, then it is possible, but no mechanic I know spends 2-3 hours troubleshooting the cars like this (hence I do it myself and just pay for fixing, or even just fix things myself). 

[H3XME]

3 hours ago, Sponelis said:

My mechanic just came back to me saying he could not find a hole near 02, so it must be the cat then..

It wouldn't be unusual. My secondary cats died at ~140k on my last IS250. De-cat time! Secondary decat will let you pass emissions if it's tested hot.

[H3XME]

3 hours ago, Mr Vlad said:

Lucas. An O2 sensor spacer is a spacer. What it does is enlarge the gap between the sensor head and the gubbins in the exhaust. The reason why some folk use them is it helps reduce wear on the sensor. It's meant to be illegal also I've read somewhere. I believe they use spacers for race cars.

I see. Thanks Vlad!

[H3XME]

2 hours ago, Sponelis said:

I am trying to take to one more garage who worked on Lexuses before, maybe they will help me there. It's just a shame that mechanics want to change the part straight away without spending enough time on the car to eliminate other possibilities..everyone is just too busy.

Rogue Motorsport in Rugby are heavily into Toyota cars. Maybe hit them up and see what they say / if they can fit you in.

[Spark plug]

This happened to my car at that age and i found my pipes between the first and second cats were badly rusted and blowing out behind the heat shields before the second o2 sensors. had new pipes welded in and that was 2 years ago and had no problems since.

[ColinBarber]

Hole in exhaust and upstream O2 sensor seem to be the main cause of this error across different Toyota/Lexus vehicles. Faulty cat is a possibility but should only be considered if the other possibilities has been ruled out because they can be checked without the expense of replacing parts.