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I have a 2006 Lexus LX 470 and I’m getting the check engine light on. I have a reader and I am seeing P0430 “ catalyst efficiency below normal (bank 2). I took some data from the sensors and plotted it but didn’t really understand it that well. Was wondering if anyone could tell me if this reflects a bad catalytic converters or not. Not sure why the downstream sensor voltages would be different. My understanding was that the downstream sensor traces would be oscillating like the upstream of the cat was bad though. Thanks for any help. O2 Sensor Data

EDIT (adding catylytic converter temperature plot): Note: T0 on this plot is not the same as T0 on the top plot. This was taken after that data set. Catylytic Converter In/Out Temperature Data Sorry the plotting software ran the graphs together.

clintsmith
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  • Welcome to Motor Vehicle Maintenance & Repair! How many miles are on the rear O2 sensors? – Pᴀᴜʟsᴛᴇʀ2 Mar 16 '18 at 16:43
  • Thanks Paulster2! Good point. Just a couple of hundred on the downstreams(I used Densos). Not sure on the upstreams. We just bought the vehicle a couple thousand miles ago but didn’t have that record. Was going to try replacing upstream but they’re significantly more expensive so wanted to try and get it right before throwing too much money at it. – clintsmith Mar 16 '18 at 17:13
  • @csmithmaui could you give the label for the various colors on the graph? I am making some assumptions that the red and blue are the downstream O2 sensors but I am not sure... – Ukko Mar 16 '18 at 17:19
  • @Ukko Hi Ukko, there is a legend at the top right. You are correct that the red and blue are the downstreams. Red is Bank 1, Sensor 2(B1S2) and Blue is Bank 2, Sensor 2(B2S2). Hope that helps. Thanks! – clintsmith Mar 16 '18 at 17:27
  • Does this answer help you any? – Pᴀᴜʟsᴛᴇʀ2 Mar 16 '18 at 18:04
  • You mentioned that you replaced the downstream sensors yourself. Would it be hard to swap them? The red line looks pretty sketchy. If it moves over to the other bank you might have a bad sensor in the mix. I am suspicious of the on/off quality of the measurement, it feels electrical. – Ukko Mar 16 '18 at 18:53
  • @Pᴀᴜʟsᴛᴇʀ2 That video is helpful. I watched that a while back to get to the point where I am now, but still was uncertain about what I was seeing. – clintsmith Mar 17 '18 at 05:06
  • @Ukko That's a good suggestion. I had the dealer pop them in for me, but I could probably swap them myself. I was going to do the upstreams myself if it's needed. Just a note, the spike in the red line came when I revved the engine up a little and held it. I don't recall the RPMs I held it at though. Not too high. – clintsmith Mar 17 '18 at 05:08
  • What are the exact voltages on that b2s2 o2s? What’s the b1s1 voltage? Roughly 3.3v? Is this at idle? That MY Lexus uses AFR sensors on the upstream. at idle I’d expect the rear o2 to stay stable around 700mV. What are the fuel trims and what are the conditions when it’s setting the code in freeze frame? As others mentioned the b1s2 looks abnormal. Can you force the sensor lean by pulling a vacuum hose? – Ben Mar 17 '18 at 05:49

3 Answers3

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Bank 2 Sensor 2 seems stuck rich.

I'm more suspect of the downstream Bank 2 sensor - it's a flat line. As long as it's up to temperature, it should show swings back and forth relative to the upstream sensors.

I'm not sure you're hot enough (Not ECT, catalyst temperature). I'd love to see the same graphs after some spirited driving.

It appears they went closed loop at time 130, and Bank 1 responded as I would expect to a rich event around time 630.

Bank 2 seems anemic. Ukko's suggestion of a swap makes good diagnostic sense.

SteveRacer
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  • If the cats aren't warmed up after 10 minutes, I'd be highly surprised. – Pᴀᴜʟsᴛᴇʀ2 Mar 16 '18 at 23:54
  • 4.7 V8 at idle? I wouldn't be. I'm not referring to the [H]O2S, I'm referring to the entire cat(s). – SteveRacer Mar 17 '18 at 00:00
  • Dunno, 'cause I've never ran one, but since the coolant has come completely up to temperature, it seems likely the cats would as well, considering they are in the direct flow of the exhaust. Would be an interesting test to see just how long it does take :o) I know my 5.3L V8 would be completely warmed up at that point, cats and all. – Pᴀᴜʟsᴛᴇʀ2 Mar 17 '18 at 00:04
  • Anyway, +1 because I agree with your overall assessment. – Pᴀᴜʟsᴛᴇʀ2 Mar 17 '18 at 00:09
  • I'm only guessing myself, but how would coolant temperature matter? The cat needs a lot of oscillation between HC and OSC to get the furnace going. Along with a decent (non-idle) exhaust flow. In any case, one of those two Sensor 2 graphs just ain't right... – SteveRacer Mar 17 '18 at 00:10
  • I was just commenting about the coolant, because from my perspective, it would take coolant longer to get to operating temps than it would the cats because the coolant is being indirectly heated, where the cats are being directly heated. How long does it take before you can burn your hand on an exhaust manifold? Not long. Yes revving the engine would get everything warmer quicker. It only takes an engine about 2 mins or less to go into closed loop. Something's got to be warm for it to get there, eh? – Pᴀᴜʟsᴛᴇʀ2 Mar 17 '18 at 00:36
  • You can burn your hand at about 150 F. Cat doesn't even "light" until 500-600 F. Typical running range in the honeycomb is probably around 1400-1600 F. (What hand are you talking about? Silvadine won't help!) Agreed that the cats are directly heated, but ONLY if the idle strategy purposely strays occasionally rich to keep the furnace fueled. They usually do, but for the primary O2 feedback. You might be right. My point is that my ancient [rusty] spidey sense likes to generate those graphs on the road, after a WOT to highway speed, and then examine the cruise voltages for S1 and S2. – SteveRacer Mar 17 '18 at 00:45
  • As an aside, one of the best ways to determine cat health is to take a laser infrared pyrometer measurement at the input and output tubes of the cat. If you don't see a 200 F higher reading at the output, either the cat isn't hot enough yet to do catalyzation (sp?) magic, or your cat is true P0420 and done. This is a nice test, because it doesn't rely on any O2 or ECU stuff. Just pure physics. – SteveRacer Mar 17 '18 at 00:49
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    Agreed on the heat differential and using it to determine health of the cat. \ – Pᴀᴜʟsᴛᴇʀ2 Mar 17 '18 at 00:50
  • Thanks for your help @SteveRacer and @Paulster2! I did take some temp data right at the end of my diagnostic but it was not with a pyrometer. I'm not sure if the O2 sensor can sense temperature or what but my reader gave me the option to see and record the temp at each O2 sensor. I'll post a plot to my question so you can see. It basically shows that the input to both cats is about 30-26.5 degrees hotter than the output, which is around 760F after the entire run. – clintsmith Mar 17 '18 at 05:17
  • I think swapping the downstream sensors is a good idea as well and agree that the B2S2 seems off. My intuition was telling me that might be the case, but wasn't really sure. – clintsmith Mar 17 '18 at 05:23
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Have a look at Test 2 in this answer.

According to it, Bank 2 Sensor 2 (B2S2) is pegged rich in the plot, which is fine.

Bank 1 Sensor 2 (B1S2) is not fine; it should not be oscillating up and down like that.

Zaid
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from the inlet and outlet temps of the cat which are about the same, i'd say the cat is not doing its job...there must be around 200 deg difference between the inlet and outlet temps-outlet being the higher one.

fekeyrse123
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