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Codes P0420 and PO430

Tiny
LEXUSIS250
  • MEMBER
  • 2006 LEXUS IS 250
  • 2.5L
  • V6
  • 4WD
  • AUTOMATIC
  • 130,000 MILES
The engine runs great but I get a po420 and po430 code. The cost temperatures are between 40 and 100 degree different from upstream and downstream locations. All four o2 sensors are new. The upstream stays steady and the downstream readings move up and down adjusting it self when throttle is depressed. At idle it stays steady as well. Catalytic converter temperature goes up when throttle is held at 2,000 rpm's and according to temperature reads on scanner the difference in catalytic converter temperature is within 20 to 40 degrees on scanner. This is driving me nuts can someone please help? Still having p0420 and p0430 codes.
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Friday, August 30th, 2019 AT 12:33 AM

4 Replies

Tiny
SCGRANTURISMO
  • MECHANIC
  • 4,897 POSTS
Hello,

These two Direct Trouble Codes (DTC)s are for each of your vehicle's catalytic converters being done with there useful life. DTC P0420 is for the exhaust on the number one cylinder bank of the engine and DTC P0430 is for the other bank. Basically, through normal wear and tear, they are not catalysising anymore and need to be replaced. Here is a link below for you to go to explaining how to do it:

https://www.2carpros.com/articles/catalytic-converter-replacement

Please go through this guide and get back to us with how everything turns out.

Thanks,
Alex
2CarPros
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Friday, August 30th, 2019 AT 4:42 AM
Tiny
LEXUSIS250
  • MEMBER
  • 2 POSTS
Figured it out. Believe it or not there was a small exhaust leak between catalytic converters and sensor 2 left and right side. Couldn't hear anything and when I placed my hand carefully over the flange I felt it. Repaired the leak and bingo! No more po420 or p0430 codes. Thank you for the help!
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Friday, August 30th, 2019 AT 11:41 AM
Tiny
SCGRANTURISMO
  • MECHANIC
  • 4,897 POSTS
Hello again,

Just for informational use here, the upstream O2 sensor(the one closest to the engine on each bank of cylinders is the O2 sensor that the Power-train Control Module (PCM) or "computer" uses to keep the air:fuel ratio as close is at can to stoichmetric or 14.7:1. The downstream O2 sensors are the sensors that the PCM uses to check the health of the catalytic converter. This is the only job of the downstream O2 sensor.

Thanks,
Alex
2CarPros
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Friday, August 30th, 2019 AT 8:07 PM
Tiny
JIS001
  • MECHANIC
  • 3,409 POSTS
Good job! That is actually the first step in diagnosing catalytic converter faults since as SCWICKEDSTANG stated earlier the rear oxygen sensors job is to measure oxygen content. The catalyst monitor does an oxygen storage test to evaluate the catalyst health. Too much oxygen will cause nitrogen oxides to elevate and If you were having a tail pipe test done you would fail for Nox! Too much oxygen like an exhaust leak fools the sensor.

That is the reason why most states now rely on check engine, and monitors completed to decide if you pass or a fail a smog test. Too many cheaters would probe the the exhaust side that would pass instead of using both probes for an accurate test. But glad to hear you figured it out.
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Friday, August 30th, 2019 AT 10:48 PM

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