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Code P0420 Catalyst System Efficiency Below Threshold (Bank 1) Diagnosis

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Old 01-31-12, 04:09 PM   #1
Lavrishevo
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Default Code P0420 Catalyst System Efficiency Below Threshold (Bank 1) Diagnosis

99 LS400:

Is there a way to check catalytic converters before buying new ones and replacing? Due to where I live I am wary of diagnosis and shops wanting to charge you the most they can.

During the inspection I checked the down pipes and cats and did not feel or hear an exhaust leak but I am not convinced the cats are bad at only 67,000 miles. Any advice and how to proceed outside dealer prices?

Also, does bank 1 refer to a specific side and if so which side?
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Old 01-31-12, 04:43 PM   #2
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bank 1 = front drivers side (LHD)

seafoam the car (search) to see i you can see the leak that way, usually it's the cat-header or cat-y-pipe gaskets
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Old 02-01-12, 07:12 AM   #3
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Typically its the second 02 sensor picking up from the secondary cat if that helps you any.
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Old 02-01-12, 07:34 AM   #4
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So the most common symtoms would be in leak, O2 sensor, then cats?

I'm going to do the Seafoam to check for leaks first but then is it better to do the second O2 sensor after the cat correct?

One guy is telling me cats should be replaced after 55,000 miles anyway. Any truth to this? Personally, I was under the impression to leave them be till the go bad. Looking at the cats the other day they look clean and are not corroded or rusty whatsoever.

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Old 02-01-12, 08:00 AM   #5
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Reset the code and see if it comes back.
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Old 02-01-12, 09:41 AM   #6
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I just reset the code and also did the Seafoam treatment to the engine and changed the oil. I'll wait to see if the code comes back and then go from there. This car idles at such a low RPM and is so smooth it's amazing
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Old 02-01-12, 10:56 AM   #7
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Should take about 60 miles of driving for it to reappear. If it does look up "anti-fouler's".
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Old 02-01-12, 11:28 AM   #8
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I'm am expecting it to come back as well. You know, after the Seafoam treatment to the engine and an oil change my idle RPM when in gear dropped 100 RPM's. I don't know if it's normal but I swear it looks like it is idling at 400 RPM's and smooth as no tomorrow. This car can beat traffic and not even break 2000 RPM's if you want. Amazing.
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Old 02-01-12, 03:13 PM   #9
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when you did the seafoam did you see any smoke leaking out near the headers? that was the point you know...lol, to make it easier to spot exhaust leaks since they are notorious for causing P0430 and P0420 in these cars.
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Old 02-01-12, 04:36 PM   #10
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Quote:
Originally Posted by PureDrifter View Post
when you did the seafoam did you see any smoke leaking out near the headers? that was the point you know...lol, to make it easier to spot exhaust leaks since they are notorious for causing P0430 and P0420 in these cars.
I have not done that procedure yet. I just did an oil change and flushed the engine with about 1/2 of the can of Seafoam. When the check engine light comes back I will do the Seafoam in the intake and check for leaks while the car is up on the lift at the muffler shop. I figured it is best to have help when trying find the leak and the right place to see where the leak may be.
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Old 02-02-12, 03:40 AM   #11
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If my code returns and I do not have an exhaust leak what if I switch the post catalytic converter O2 sensor to the other side, reset the code, and see if it comes back as P0430 on bank 2? Just thinking outloud of an accurate way to eliminate everything else befor replacing the cats.

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Old 02-02-12, 06:29 AM   #12
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worth a try, use anti seize.
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Old 02-03-12, 12:42 PM   #13
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Quote:
Originally Posted by billydpowe View Post
worth a try, use anti seize.
Just an update. I have not had time to switch the post-cat O2 sensor yet but I did call multiple dealers in the US and spoke with several service advisers. They all agreed that if I did not see and feel any exhaust leak that it would almost definitely be the cat. They said 02 sensors have their own codes when they are failing or fail. I'm still going to do my extensive leak test and switch 02's just to be sure but I wanted to mention what they instructed me on. This is good info to learn though.
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Old 02-04-12, 07:08 AM   #14
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Well so much for doing my leak test... Went to a different muffler shop and they are installing two new magnaflow cats as I type. $400.00 plus tax. Probably the best deal I can get here locally without getting the parts myself and shipping to PR can jack the price up so much at times it's not worth it. I'll post some pics up later. Fingers crossed this is the problem. Call me neurotic but I just can't stand driving with a check engine light on...

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Old 02-04-12, 10:27 AM   #15
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New cats are in and code is reset! Car feels good. Could be just me but it feels like she moves ever so more easily. Here is to hoping the it's not the 02 sensor. Nonetheless, I'm sure the cats were overdue at 13 years old.
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Old 02-04-12, 10:27 AM
 
 
 
 
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bank, catalyst, check, code, efficiency, engine, es300, is250, lexus, ls400, p0420, seafoam, system, threshold, treshold

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