2009 GX470 O2 sensor/catalytic converter question (1 Viewer)

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CloudCity

LuxCruisers
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I am helping out my bud who bought a 2009 GX recently since I have a 100-series LX and like to poke around these rigs. He had the classic Traction/Engine lights pop up and I ran the codes. Showed "P0420 Catalyst System Efficiency Below Threshhold." I cleared the code and we too it for a drive of about 40-mins and the lights didn't reappear yet. I did note that my OBDii showed a reading for Sensor 2 of 80, but that Sensor 1 showed 0.00 readout.

My questions are does this indicate an O2 sensor failure, and if so, how do I determine which on on that bank 1?
Also, might this indicate a catalytic converter issue, or is it most likely an O2 sensor?

Thanks much!
 
Happens to my LX on long trips. I just clear it and wait until the next long trip when I need to clear it again. Sometimes it's a few months in between, sometimes weeks. Zero change in mileage or any other measurable metric as best I can tell (and I track every single gallon).

Long term I need to find the root of it as well. But in the short term, it's likely of little concern.
 
Code should say bank and sensor. I get them after I drive city and get on the highway (especially with altitude change). I just clear them. If they come back persistently, swap the sensor with a denso unit. Do not use Bosch.
 
Thank you much, appreciate that. Hasn't re-appeared since clearing.
 
Just did all 4 sensors.

Rock auto had the best deal on Densos that I could find if you end up going that route.

Did you do a write up on it? Trying to determine if this is in my ability to do...
 
Did you do a write up on it? Trying to determine if this is in my ability to do...
I did not do a write up.
For the upstream sensors, they seem to be designed for a service tech with tiny hands and long skinny arms.

It was a challenge for me and I consider myself very mechanically inclined.
 
I wanted to come back to finalize this thread since I forgot to, but the GX ended up needing one Cat replaced. The code came back after a few weeks. That was what finally resolved the code reappearing.
 
I wanted to come back to finalize this thread since I forgot to, but the GX ended up needing one Cat replaced. The code came back after a few weeks. That was what finally resolved the code reappearing.

mid you don’t mind me asking, how much did the cat end up costing you?
 
mid you don’t mind me asking, how much did the cat end up costing you?
The GX belongs to a friend but we just checked his paperwork from when he had the repair done at the local Lexus dealer and it was $945 for the part and a grand total of $1,567.56 for the full repair including diagnostics, labor, and associated gaskets, etc. Mind you these are all Lexus dealer prices. Our local (Kuni Lexus of Beaverton/Portland) is a top notch operation tho and I use them for some things too.
 
Thanks for the update. I'm getting both P0420 and P0430 appearing constantly for the last few months. Clearing the codes only lasts 20 to 40 miles.

My code reader only tells me that it's bank 1 for P0420 and bank 2 for P0430, but not which sensor.

Since I replaced the pair of downstream sensors 4 years ago, I'm going to replace the pair of original (18 year old) upstream sensors this time around with Denso ones from RockAuto.

Best case scenario, the upstream sensors fix my issue so I can pass the smog test coming up in a month or two.

Worse case scenario I need to replace the upstream cats at God-knows what price. Parts seem to range from $450 to $650 each depending on web site and if toyota or lexus brand. So, I figure pray and hope the cheap parts fix the issue.

Anyone know if these are the right part numbers?

17105-50170, Cat Converter with Integrated Manifold (Left = Drivers side in USA)
17104-50180, Cat Converter with Integrated Manifold (Right = Passenger side in USA)

Parts seem to be cheaper if I buy for Toyota 4Runner 8-cyl than Lexus GX470, but only like $40 cheaper each.

2376C96A-4BCF-462E-8410-FBF191D8C009.jpeg
 
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Hmmmm, my buddy's invoice shows 17150-50050 as the "left side catalyst" manifold assembly.
Also:
17198-50010 for manifold gasket
90080-43036 for exhaust pipe gasket
90080-17187 nut, lock (x8 pieces)
 
Thanks for posting the part numbers for the 2009 gx470. I have a 2003 and it looks like 2003-2004 use a different part number for the integrated cats than the 2006-2009
 
Thanks for posting the part numbers for the 2009 gx470. I have a 2003 and it looks like 2003-2004 use a different part number for the integrated cats than the 2006-2009
Glad we figured that out, thank you! I believe my friend's GX is an '09.
 
Any updates on the fix? I'm getting same two codes but I don't think its the O2 sensors. I'm leaning towards (maybe) bad cats and/or vacuum/exhaust leak on bank two (causing lean condition resulting in compensating with higher LTFT) due to higher LTFTs on bank two (and the rich idle conditions on downstream sensors). All 02 sensors track from lean/rich depending on the driving condition.

Data Logs
 
4-5% LTFT's are not terrible. Even a small vacuum leak should give you LTFT's that are 15+%. You can check for a vacuum leak fairly easily by spraying carb cleaner (or propane from a unlit small torch) at various places where you think you might have a vacuum leak, and watching for negative spikes in the STFT (it will instantly spike negative when you find the leak).

Regardless, I'd still just replace the sensors, to rule them out. Depending on what year GX you have, they are a minimum of 13 years old. You can save a quite a bit of money and use Denso universal sensors. They are exactly the same as the OEM sensor, but don't have the connectors on them. You unhook the OEM sensor, then cut it's harness and splice in the Denso sensor using a heat shrink butt splice connector. If you do that and still get codes, it might be your cats, but it's worth ruling out everything else first.
 
Mine is an 09. I'd normally agree about just replacing the 02 sensors. I bought them before I did any further diagnosis. I don't think it will fix it. And I've got a month to return them. How can I check the cats? Take the exhaust off and look in? And these are integrated exhaust manifolds/cats right? I didn't see/hear any obvious damage to them.
 
On a well-maintained vehicle, the cats should easily last 200K and they might even go well beyond that. The cat is just a metal honeycomb with a special coating of precious metals that burns off excess fuel/pollutants. However, they can become damaged if your engine is running too rich due to some other problem (leaky injector, bad upstream O2 sensor), which will cause a lot of fuel to be dumped into the cats, which will burn and basically overheat them. Other things like oil burning or coolant getting into the cylinders will also kill a cat, but they are unlikely to occur on a GX unless it has been severely abused.

The best way to check them is to have known-good upstream and downstream O2 sensors (by replacing them with new Denso sensors) and comparing the readings as the engine is running. There are some YouTube videos and other resources online that show hot to diagnose them. Since you already have a datalogger and can plot the sensor values, it should not be too difficult. But, the diagnosis will be suspect unless you are 100% sure both your upstream and downstream sensors are good. The cats are very expensive ($700 per side as they are integrated into the exhaust manifold, and they R&R is pretty difficult), so they are not something I would want to replace without first ruling out the O2 sensors by replacing them. I ran into the same problem on another vehicle and eventually isolated it to the upstream O2 sensor connector - once I cut it out and hard-spliced it to the sensor I stopped getting PO420 codes. The downstream sensor was totally fine.

A faulty upstream sensor can trigger both upstream AND downstream sensor codes, AND cause the somewhat elevated LTFT values you are seeing (but you should also rule out a vacuum leak as mentioned above), AND eventually cause your cats to fail by dumping in too much fuel.
 
On a well-maintained vehicle, the cats should easily last 200K and they might even go well beyond that. The cat is just a metal honeycomb with a special coating of precious metals that burns off excess fuel/pollutants. However, they can become damaged if your engine is running too rich due to some other problem (leaky injector, bad upstream O2 sensor), which will cause a lot of fuel to be dumped into the cats, which will burn and basically overheat them. Other things like oil burning or coolant getting into the cylinders will also kill a cat, but they are unlikely to occur on a GX unless it has been severely abused.

The best way to check them is to have known-good upstream and downstream O2 sensors (by replacing them with new Denso sensors) and comparing the readings as the engine is running. There are some YouTube videos and other resources online that show hot to diagnose them. Since you already have a datalogger and can plot the sensor values, it should not be too difficult. But, the diagnosis will be suspect unless you are 100% sure both your upstream and downstream sensors are good. The cats are very expensive ($700 per side as they are integrated into the exhaust manifold, and they R&R is pretty difficult), so they are not something I would want to replace without first ruling out the O2 sensors by replacing them. I ran into the same problem on another vehicle and eventually isolated it to the upstream O2 sensor connector - once I cut it out and hard-spliced it to the sensor I stopped getting PO420 codes. The downstream sensor was totally fine.

A faulty upstream sensor can trigger both upstream AND downstream sensor codes, AND cause the somewhat elevated LTFT values you are seeing (but you should also rule out a vacuum leak as mentioned above), AND eventually cause your cats to fail by dumping in too much fuel.
The only issue is the PCM does its own 02 sensor checks and has codes for each 02 sensor. And from the data I'm seeing all the 02 sensors are still working.

I did have another vehicle (Toyota Highlander) that had the cats replaced, but not the 02 sensors and still had the codes until 02 sensors were replaced, so I get your point. Just hate replacing $300 worth of sensors before $1500 more worth of parts. I'm at 235k miles. It could likely use a tune up at the same time. Any way to check for leaky injectors? I'll log fuel pressure and misfires to see if anything else is weird. It seems to run great otherwise.
 
The only issue is the PCM does its own 02 sensor checks and has codes for each 02 sensor. And from the data I'm seeing all the 02 sensors are still working.

I did have another vehicle (Toyota Highlander) that had the cats replaced, but not the 02 sensors and still had the codes until 02 sensors were replaced, so I get your point. Just hate replacing $300 worth of sensors before $1500 more worth of parts. I'm at 235k miles. It could likely use a tune up at the same time. Any way to check for leaky injectors? I'll log fuel pressure and misfires to see if anything else is weird. It seems to run great otherwise.
The O2 sensor may work to some degree, but may not be giving an accurate reading. At 235K, it would not be unexpected. You can get the universal Denso O2 sensors for $34/each on Amazon ($150 for all 4, plus $10 in splices). I personally consider the O2 sensors at tune up item, replacing them every 100-150K is a good idea to keep your engine running well (I'm at 151K so I need to do them myself sometime :)).

Leaking injectors are pretty uncommon, but if you did have one you'd have a black spark plug at that cylinder, while all of the others would be fine. So probably a good idea to change your plugs (who knows how many miles they have on them unless you are the original owner) and inspect while ruling out that issue.
Amazon product ASIN B000C5WCUE
 

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