popek31

Hi, dear Lexus users,
I am facing down by P0430 code. I am aware of possibile causes :
- Gas leaks from exhaust system
- Air fuel ratio sensor (sensor 1)
- Heated oxygen sensor (sensor 2)
- Front exhaust pipe assembly (TWC: Front and rear catalyst)
- EGR valve assembly

But can someone suggest probable cause by Sensor 2 measurements from OBD2, placed below ( from top to bottom : Engine RPM, SPEED (km/h, both Sensors 2 ) ?
Thanx in advance

SILENTM

Catalytic converter is going bad p0430 is bank 2 cat efficiency. Blue line is going up and down (rich to lean) which means it is following the pre cat sensor. which in terms means the sensor is good and picking up unburnt fuel which the cat is supposed to burn off. So as you can see when you revved up the engine for a split second you are dumping extra fuel into the engine and the cat cant burn off the excessive quick enough

popek31

It means both cats are bad because blue line on third diagram is "O2 Sensor Voltage - Bank 1 Sensor 2" ( OBD2 code 0x15 ) and green line on third diagram is "O2 Sensor Voltage - Bank 2 Sensor 2" ( OBD2 code 0x19 ).
For me is strange that after lowering engine rpm (point 1720) Sensor from Bank 1 gone down but Sensor from Bank 2 had ~0.7V.

Let me show more measurements from this ride, because previous was from last part of the ride.

aristo1987

I have a stock midpipe with both catalytic converters for sale. Lmk...you can check out the sales thread or pm directly.

canatto

Sensor 2 is sometimes referred to as Cat performance monitor -- what it does is to tell if the cat is working and how well. It is located down-stream the front Cat converter, and is supposed to read a smooth trace looking like the green trace in the 3rd picture. A switching waveform like the blue one means the exhaust being read by that sensor is alternating between rich-lean all the time -- meaning the Cat converter upstream that sensor isn't doing its job well.

There is only one remedy, change the failed converter. It will be costly.

My cheap "fix" is to cut the sensor wires (not the heater wires) and splice in a simple low-pass-filter, or LPF, consisting of a resistor and a capacitor. This LPF smooths out the switching part of the sensor output and let pass only the average, so that the cat converter appears good seen by the engine computer. I use a 10K-ohm resistor and a 47uF capacitor, they are tiny SMD parts. It's important to waterproof the LPF and the splice, but it's not hard to do for one who's into basic electronics.

I do not worry about added pollution by doing the "fix", as there is another cat converter downstream the sensor 2 that handles the polluting components in the exhaust gas get passed the upstream converter. My car passed emission with high scores every time for years.

3lex3

Hello I have a 2006 Lexus gs300 that jus mysteriously started to have cat issues ,I originally bought car with trans issues that caused cel but it would set all monitors with no issue ..I sent ECM to be reflowed and when I got it back it did not fix the trans issue and and the 02 sensor would not ready but not throw a code I sent car into transmission shop for a flush and sensor change while their for a bout a month when they got the tech in to do diagnostic he said the car was throwing catalyst codes I was like how 🤔they had the car for. About a month and I kinda felt they did something to it idk ..but I took it to another shop and had trans replaced car left the shop with no codes..all monitors set and at the same time it threw p0420 and p0430 codes as pending but no cel I kinda of think it's the ECM but idk their know for ECM issues ..but do you have a diagram of the compactor and resistor you used to go in line for the cats

canatto

Attaching the diagram.
There are 4 wires coming off the sensor. Don't touch the black wires, they are the heater power wires. Cut the other two wires, white and blue, and splice in the LPF.

3lex3

Thanks for the reply and the diagram I'm going to try this afternoon I run down the current fuel and try catylic cleaner and barryman intake and fuel injection cleaner
I jus have a problem really believing the catylic converters are bad ,I'm leaning to believe that it's the ECM ,I have a new that I think I may install since I can't return it ,.this is my second Japanese car that I have restored and it has not been going well it has been worse than all my German cars Mercedes and Audis

2006 Lexus Gs300
Tha kd again and I will keep you posted on results

canatto

I wish you good luck. I should have been more clear about the capacitor. Try to get a ceramic chip capacitor for it, and not to use a electrolytic cap, as the latter requires proper polarity DC bias to perform, unless it is a non-polar type electrolytic cap.