[FIXED] Lexus 2002 3.0 L PO430 catalyst efficiency below threshold

this car runs fine except for the code PO430.

I have attached image of both O2 upstream and downstream sensors for Bank1 and bank2.

(1) For O2B1S1, the blue trace (upstream sensor, ChA) shows a normal upstream waveform changing from 100mv to 800mv at 2500 RPM, while the red trace (ChB) somewhat erratically changes from 750 mv to about 300mv . On the next trace, at deceleration, the red trace slightly dips and then almost goes somewhat straight, with the blue trace slows in frequency.

(2) For O2B2S1, the blue trace (upstream O2, ChA) exhibits the same characteristic in amplitude and frequency with B1S1@ 2500 RPM.
However, the red trace (downstream sensor, ChB) is somewhat constant in amplitude of 0V @ 2500RPM, and then at decel it rises momentarily at about 950mv and then slowly decreases in amplitude to about close to 0V.

My question is: does the B2 upstream red trace merit a cat low threshold as it shows a a close to 0V and then spikes at decel momentarily and then gradually decreases as compared to an almost steady upstream trace on B1 ?

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pardon the extra pictures,,,i dont know how it replicated the images.

Hey robert! Any chance of an exhaust leak near the B2S2 sensor? 'Cause it sure looks like there's an excess of oxygen getting picked up by that sensor. I don't recall if this vehicle still uses the goofy Toyota sensor gaskets or not. If so, they leak like it's their job. :lol:

If there's no leak, the trims are reasonable, then I'd say the bank two cat isn't storing oxygen at all. The 'A/F LEAN/RICH' bidirectional test in the scanner is fantastic for measuring oxygen storage and gauging sensor response time.

As above erratic readings make me look for an exhaust leak , but I think you need to do a forced rich- lean test (Oxygen Storage test) to test the cat.

hi Tyler and Andy...I havent checked for any leaks close the B2S2. I will double checked do as advised by Andy re: force rich/lean condition. I will let you know of what I find. Thanks guys, appreciate it greatly.

I checked for leaks and there is none. My next step is to force feed propane and scope all sensors and watch how it behaves alongside STFTs on scanner. I will try to
attach waveforms.

Unfortunately my propane tank was empty...

I re-scope all upstream and downstream sensor.
1. blue trace - B1S1
2. green trace - B1S2
3. red trace - B2S1
4. yellow trace - B2S2

B1S2 shows a delay indicating oxygen being absorbed by (B2) catalytic; However I cannot make out B2S1 ans B2S2. But it seems B2S2 remained close to 0V from idle to 2500 RPM and then spiking upon decel and then drops shortly after the 35.0 ms point.

Is this enough to condemn the B2 cat?

Did something go wrong with the red trace? I see it go dead flat line part way though. :blink: Also, are you positive you've got the traces labeled correctly? Because to me it looks like you've got the two upstream sensors as blue and green, and the two downstream as red and yellow.

Otherwise, it looks like the bank one cat is hollow, and bank two is out of fuel control. :silly:

Hi Tyler...I had to redo the traces. I made sure that my probe pins are on the right wires so here goes and tell me what you think.

Thanks Robert! It still looks to me like the B2S2 is struggling with amplitude. No exhaust leaks, so that makes me wonder about the sensor...

Does the B2S2 sensor EVER go over 500mV? The propane (external fuel) would answer that question. OR go for a WOT run on a highway on ramp. All four sensors should easily go rich. If you still can't get B2S2 to show rich, then I'd move to circuit integrity checks next.

thats the problem...never once did i see B2S2 spike to at least 450-500 mv. I did propane the last trace and scanner STFT showed rich, im beginning to doubt if cat is the problem. im try to recreate what Paul did in one of his video but cannot come up with delay in S2 upon decel.

Hey Tyler, Andy...this is a followup on the Lexus PO430. After erasing the faultcode, I asked owner to drive the car around fo about a week and if the check engine light would come on again to drive it to my place. He called after about two weeks driving. I jacked up the vehicle and listened for some leak...I could barely hear any. At any rate, considering it had 192 + km and sensors never changed, I decided to remove the B2S2 and lo and behold, the whole sensor and where it was plugged in gave as I was trying use unplug it !!!

I am attaching a picture of the sensor and where it was plugged. Apparently Andys hunch of a leak was correct. Owner will have the entire catalytic system and B2S2 replaced. As soon I get the car back I will scope it and compare with the old waveform and inform you guys. In the meantime this is headed for a fix...

I see what you mean! :blink: I'd say there was definitely some kind of leak there - enough of one to confuse the O2, anyway.

I bet you'll have a completed Cat monitor and good looking signals afterwards.

This is the new waveform after owner had the rear CAT and its corresponding B2S2 replaced and installed. It seems B2S2 (yellow trace) is now reacting accordingly indicating CAT threshold okay. I would appreciate your comments on this waveform...thanks

So the red trace is upstream B2? And green/blue is B1? I'm sorry to say, but I'm still not sure the downstream is reacting well. :blink: Has it passed the Catalyst monitor? In the end, it doesn't really matter what I think, as long as the car is happy! :lol:

If the upstreams are car carbon copies of each other for each bank the down streams should be similar but even allowing for a bit of aging this isn't the case.

Honestly I dont know how to make of this waveform except that B2 (yellow trace) reacting better than before; when superimposed, both B2 sensore react almost identical on the snap segment (last portion of waveform) and almost opposite in the idle and 2500 RPM. Owner confirmed B2S2 is an after market NGK brand as well as an after market rear CAT. I guess as Tyler mentioned, as long as the engine is happy and no check engine recurring.

I definitely see more of a reaction in the B2 downstream, but I'm still surprised at how much time it spends lean. :blink: Was this taken with the vehicle cold? Warmed up?

Pretty sure TID $01 is the catalyst monitor on this Lexus. If you get a chance, see if the Cat monitor has run/passed? And what TID $01 has to say.

thank you Tyler for replyinh.

yes, all test are done with engine hot; it puzzles me why B2 would stay lean. scanned PIDs using EOBD and from $01, catalyst monitor showed pass as well as both O2 sensor monitor and O2 sensor heater monitor passed and no pending DTCs (attachment). I told owner to pick up the vehicle this morning and should anything come up to give me a call. in the meantime i would consider this a fix...

Looks good to me. Well done on the fix, sir! I'm sure the owner will be happy to have it back with the CEL out.

as you said, if the engine is happy, so are we !!!

thanks a million to all advise and suggestion.