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1999 Hyundai Elantra Wagon, 2003 Kia Sedona, 2012 Kia Sedona, 2007 Hyundai Tucson
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48 Posts
Discussion Starter · #1 ·
I replaced the spark plugs today... what a PITA. 2003 Sedona with 127K miles. It still had the original plugs, so it was really hard to get apart. Anyways, I got through that. Now tonight it has a code... P0431. Bank 2 downstream O2 sensor below threshold. Any thoughts?
 

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Having exactly the same problem. Changed plugs and wires, installed new gasket, and it ran OK for 2-3 days, and now P0431. Still drives OK. It's just throwing the code.
 

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1999 Hyundai Elantra Wagon, 2003 Kia Sedona, 2012 Kia Sedona, 2007 Hyundai Tucson
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48 Posts
Discussion Starter · #3 ·
Yeah, it's weird. I suspect it's a particular weird 3.5 V6 Kia/Hyundai problem. I'm checking the Hyundai site...

Yes there's some cases of tune up followed by p0431 on the 3.5.
 

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1999 Hyundai Elantra Wagon, 2003 Kia Sedona, 2012 Kia Sedona, 2007 Hyundai Tucson
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48 Posts
Discussion Starter · #4 ·
I think it means intake air leak now. I'll try replacing the intake gasket one day.
 

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1999 Hyundai Elantra Wagon, 2003 Kia Sedona, 2012 Kia Sedona, 2007 Hyundai Tucson
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48 Posts
Discussion Starter · #5 ·
I finally got around to replacing the lower intake plenum gasket, so far no check engine light. Hopefully problem solved.
 

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1999 Hyundai Elantra Wagon, 2003 Kia Sedona, 2012 Kia Sedona, 2007 Hyundai Tucson
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48 Posts
Discussion Starter · #6 ·
Well, just to update....

Turns out my CEL came back after I replaced the intake gasket. Ugh.

I finally reasoned it must not have liked the spark plugs I used. I had purchased Bosch Iridium plugs thinking it would be the last time I ever needed to do that... but the joke was on me.

I finally bought the cheapest copper plugs I could find.... Autolite Copper, and stuck them in there. Low and behold... no more CEL after a month of driving. The problem is now the idle... it's too low. Since I can't see any reason for it to idle so low, I propose it doesn't like the Autolite copper either. Other than the idle being to low, it runs great with no more CEL. I bought OEM NGK Platinum plugs... they're sitting on the bench looking at me. I'll put them in one day when they nag me enough.
 

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2008 SpectraSX, 2014 Optima LX,2006 Jeep Liberty, Linux Mint Mate
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You should have read our forums... KIAs do not like "special" plugs especially "Bosch"... The standard NGK Iridium plugs or Densos were spec'd for this engine and the ECM doesn't like multiple electrode wizbang high end plugs.
They create multiple fires that are interpreted as mis-fires.
I just replaced motorcraft/autolite plugs in a 2000 Ford Ranger 3.0L V6 with NGKs and the owner could not believe how much better it ran..Sometimes simpler is better..
Dave
 
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