CEL with P0420 code
I have Lexus is250 (2011)
Recently I got a P0420 catalytic converter inefficiency code.
I used DPF foam to clean the catalytic converter but after only one day, I got the CEL again.
i cleared the code and came again same day.
by watching Bank 1 Sensor 2 reading, the voltages would still fluctuate between about .7 and .4
does any one know how can i solve this?
is that because my CAT is worn out?
I tried the torque pro and EOBD FACILE, I found that the O2 sensors are working properly.
(see attachment)
When the engine is running at Normal operating temperature, the O2 sensors give around 527 C for the four sensors.
So. What is the problem now?
Last edited by ameer90; Apr 19, 2021 at 10:26 AM.
I found a few videos, including Scotty Kilmer, suggesting to use one gallon of paint automotivr thinner to the fuel tank. All reported the same code as yours, and as long as the cat was not rattling, most times got rid of the code. Some report they do this to "help" pass emissions.
*NOTE, the above information use at your own discretion. I have never done this, but seems to give good results to those who have done so.
How old is the car, miles? the life of a CC is affected by how well the car has been maintained and they simply start to get "dirty" after many many yrs of use. Do check for leaks like other suggest.
Almost forgot to mention, on my 4Runner it triggers the code on certain gas stations in the area (in other words cheap lower grade gasoline). Just sayin, put some 93 Shell etc, clear the code and see if it comes back. One of my friends has a BMW, and that car will tell you quick which stations have lower grade fuel, he sticks w Shell and nothing else. I have found Circle K 93oct where I live is good quality.
Last edited by GrizzlyMan; Apr 19, 2021 at 10:15 PM.
I found a few videos, including Scotty Kilmer, suggesting to use one gallon of paint automotivr thinner to the fuel tank. All reported the same code as yours, and as long as the cat was not rattling, most times got rid of the code. Some report they do this to "help" pass emissions.
*NOTE, the above information use at your own discretion. I have never done this, but seems to give good results to those who have done so.
How old is the car, miles? the life of a CC is affected by how well the car has been maintained and they simply start to get "dirty" after many many yrs of use. Do check for leaks like other suggest.
Almost forgot to mention, on my 4Runner it triggers the code on certain gas stations in the area (in other words cheap lower grade gasoline). Just sayin, put some 93 Shell etc, clear the code and see if it comes back. One of my friends has a BMW, and that car will tell you quick which stations have lower grade fuel, he sticks w Shell and nothing else. I have found Circle K 93oct where I live is good quality.
Trending Topics
Since you have a scan tool. Check the fuel trims at idle, cruising.
If you check for exhaust leaks, and find none. Reset the codes, and the code sets instantly. The cat is toast.
Celebrating Lexus & Toyota from Around the Globe
I checked the exhaust system and there is no leak. I think the catalytic converter is clogged. Especially I notice poor engine performance. As you know, the lifespan of catalytic converter is only 10 years.
Also, before one month I heard a rattling noise two times coming from under my car, it just came for a few seconds and then disappeared. I ignored the noise because I thought it comes from the vehicle that was beside me.
I am thinking to remove the cats and cleaning them outside the vehicle by using DPF and Catalytic Converter Cleaning Machine.
See thr below O2 sensors voltage that I captured today once I’m using the cruise control system.
P0420 is related to bank 1
Last edited by ameer90; Apr 21, 2021 at 02:54 AM.

Based on the temperatures and readings fluctuating, they appear to be working. Don't count them out yet. It could be the sensors getting sluggish.
What fuel treatment products are available over there?
Based on the temperatures and readings fluctuating, they appear to be working. Don't count them out yet. It could be the sensors getting sluggish.
What fuel treatment products are available over there?
my car does not consume oil. I will remove the cats and clean them to avoid any damage to my engine.
I always use 95 octane gas.
but I want to know how many cats does Lexus is have? 2 or 4?
Is that on the picture a catalytic converter? If yes, does it affect the ECU if I remove it? Because it’s located after O2 sensor.










