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.

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..

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?

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.

1 hour ago, Mr Vlad said:

Hi Simonas and welcome to the best Lexus forum there is. Regards your issue. No harm in cleaning the MAF sensor with a dedicated spray. 

What kind of fuel do you use? How does your car drive? Is it sluggish? Do you get any smoke from your exhaust? 

If your car drives normally then disconnect your battery and leave it disconnected for 45 minutes. Re connect the battery and see if the warning lights appear on the dash. If they don't then all good.

If they reappear after a short time then use a fuel additive like Millers Oils petrol ecomax. It cleans injectors and the fuel system and peps up the petrol. 

Hi Mr Vlad,

I use E5, car drives perfectly fine, however couple of times I had revs going up and down on its own when idling and then it stopped after like half a minute. Haven't seen any smoke from exhaust, apart from early morning on cold start, which I assume is normal.

Lights have been cleared by my mechanic today, I drove circa 40 miles afterwards and it hasn't reappeared yet.

Ill try to clean MAF. I could try the additive as well, but my mechanic said it shouldn't be anything wrong with the injectors as error code is appearing on both banks, meaning something else triggered it.

Hi all. I have got Lexus IS250 2007. Couple of days ago check engine light and check VSC came on at the same time. My mechanic tried to diagnose the car and got codes P0172 and P0175, both banks are too rich. He did some more tests and the long term fuel trims were showing -25. All of the sudden something happened to the engine and fuel trims became normal. He is not sure what is causing it. Reading the forums, everyone is saying MAF sensor, but he said it can’t be as he was getting good reading from it. Anyone has any suggestions what could it be and what to do next to identify the problem?