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I HAVE A 2005 MDX WITH 245K ON IT.

I'M GETTING CODES PO430 AND P0420 THAT GO ON AND OFF. MY CODE READER INNOVA 3040 SAYS BANK 1 FOR P0420 CODE (DOESN'T SAY IF ITS THE UPSTREAM OR DOWNSTREAM SENSOR THOUGH) AND BANK 2 FOR P0430 (DOESN'T SAY IF ITS THE UPSTREAM OR DOWNSTREAM SENSOR)

I'VE BEEN LOOKING AT THE LIVE DATA READINGS FOR ALL FOUR SENSORS AND NOT SURE IM' KNOWING WHAT TO LOOK FOR...

MY SUSPICION IS THE BANK 2 SENSOR 2 IS NOT VERY RESPONSIVE WHILE DRIVING STAYS IN THE 0.435 RANGE OR MAYBE THE BANK 1 SENSOR 1 IS TOO RESPONSIVE AS IT JUMPS AROUND FROM 0.2-0.80 ISH...

OK IM NOT SURE ANY OF THIS MAKES SENSE...

ANY THOUGHTS...?
 

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Bad gas can cause that, as can a lot of misfires (you should be getting codes for that if that's the case). FWIW, if you haven't done a valve adjustment in the last 100,000 miles (or ever!!!) you'd no doubt be getting misfires, or at least affecting the efficiency which could be causing raw fuel to be reaching your catalytic converters.

The fact it's happening on both banks makes me suspect something other than "bad cats" or "bad sensors" though either possibility could explain the codes.

Normally you want to see your downstream sensors NOT tracking the upstream sensors directly. If they are, it points toward "bad cats" but that can also mean a lot of different things. Sometimes it's just a matter of filling up with quality gas, and getting out on the highway and putting some miles "at speed" to clear the cats (they get hotter the faster you go, so I'll let you figure out how best to REALLY clean them out). ;-)
 

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Discussion Starter #3
I did value adjustment 15k ago...

I think it’s bank 2 sensor 2 going to try that...

I compared lice data from my 2012 mdx that has no light on to my 2005 mdx and the only difference I’d bank 2 sensor 2 doesn’t move much during driving stays around 0.400vokts...


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P0420 and P0430 are both downstream codes for "below efficiency" cat performance. P0420 for bank 1 (back side of the motor) and P0430 for bank 2 (front side). Agree with habby that bad gas could trigger that and it's unlikely that both sensors or both cats go bad at the same time, though at 245K they are definitely long in the tooth. If the car was mine I would run this tank of gas as low as I could, refill with high quality gas and run at least 1/4 of a tank before disconnecting the battery to reset the codes (make sure you know your radio & nav codes) then see if they come back.
 

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P0420 and P0430 are both downstream codes for "below efficiency" cat performance. P0420 for bank 1 (back side of the motor) and P0430 for bank 2 (front side). Agree with habby that bad gas could trigger that and it's unlikely that both sensors or both cats go bad at the same time, though at 245K they are definitely long in the tooth. If the car was mine I would run this tank of gas as low as I could, refill with high quality gas and run at least 1/4 of a tank before disconnecting the battery to reset the codes (make sure you know your radio & nav codes) then see if they come back.
Hello all,
My 04 MDX has an error code P0420 threshold bank 1, I'm trying to follow this link to help me fix this issue. I've reset the error code using OBD2 and will see if this code pops back after filling up with premium gas. Let's say if code P0420 does pop up;

1) What is the first thing I should replace? ( O2 sensor behind the engine? )
2) I'm hoping not the catalytic converter! Yikes. Too much work , cost too much.
3) car has 205k miles
4) runs great without any other check engine lights on..
5) I'm pretty handy, just need car advice.

Please help , thank you kindly
Billy_49ers
 

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Hello all,
My 04 MDX has an error code P0420 threshold bank 1, I'm trying to follow this link to help me fix this issue. I've reset the error code using OBD2 and will see if this code pops back after filling up with premium gas. Let's say if code P0420 does pop up;

1) What is the first thing I should replace? ( O2 sensor behind the engine? )
2) I'm hoping not the catalytic converter! Yikes. Too much work , cost too much.
3) car has 205k miles
4) runs great without any other check engine lights on..
5) I'm pretty handy, just need car advice.

Please help , thank you kindly
Billy_49ers
So the "below efficiency" lingo essentially means that the Cat isn't cleaning up the exhaust as much as it is supposed to. There are other codes that will indicate a failed O2 sensor, which doesn't mean it's impossible to be a failing sensor the general likelihood is the Cat itself. How you deal with it depends very much on where you live and if you have to get smog tested. If you don't live in an area that tests you can most likely do what many of us do and use the non-fouler hack. It's working just fine for me. My Cat isn't plugged so the only issue is slightly higher emissions than the system is set up to accept. Or you can just drive with the CEL on, but I hate that for two reasons. First I hate seeing the light and second once the light is on for any reason you are completely blind to other issues that would have turned on the light.
 

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My P0420 ended up being the cat. It was a DIY project - not too bad if you have the tools and patience bc the space is tight. The heat shield has to be taken out of the way to get the cat out the passenger side wheel well. I also didn’t have to deal with any frozen or rusted bolts - something to consider. (Front cat is very doable - haven’t changed it but had to get it out of the way for a head gasket replacement last year.)

That being said, you could try a bottle of Techron with better gas and next, a lower O2 sensor. They are about $40 from rockauto. It may not be the sensor but if you try this route, get the NTK.

Depending on what state you live in, online aftermarket cats are half price or less of OEM. In CA, you can’t get aftermarket but you can get OEM online. I went with an online Honda dealer to avoid the Acura mark-up. Be sure to get gaskets for both ends of the cat.

Good luck!
 
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