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code P420 keeps throwing cel


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My apologies. Based on what the mechanics had been telling me, I assumed teh code was P0240 and replaced the rear O2. However, the CEL came back on after a few days so checked it myself using a co-worker's scanner. Code thrown is P2097. Ordered pre-cat O2 yesterday from Amazon.

 

Will see what happens.

 

If per cat o2 fails, you should get horrible MPG. Any updates?

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If per cat o2 fails, you should get horrible MPG. Any updates?

 

 

You're right! Mileage seemed to be getting worse for some time and performance became somewhat sluggish and sporadic. A/F Sensor was installed Thursday. Some 400+ miles later, all seems better and no codes thrown yet! At times, I think acceleration is sub par, other times it seems alright. So hopefully, this problem has been dealt with.

 

Side note: The local dealership readily told me I may be looking at a CAT replacement. They reset the code and told me if it came back, we'd be loking at replacng the converter. This forum saved me some unnecessary aggravation and $$$!

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That's unusual. Where do you buy your gas? In the USA, most gasoline contains at least 10% ethanol to reduce the formation of smog. It adds oxygen to the gas to help it burn cleaner. Yes, it does hurt performance and gas mileage and can throw some engines for a loop, but 95% of engines run fine on it. Make sure you get quality gas (stay away from 7-11 gas, or any other small station). I use Arco (don't hate me. Some love it, some hate it. I use it ONLY because it's 30 to 50 cents cheaper than any other gas (Shell, Chevron, 76). I don't get good mileage and I can't really afford to put $4.05/gallon gas from Shell or Chevron in my car. And gas is getting more expensive by the week here. Soon it will be $4.15, then up to $4.25-$4.30 by mid July. I haven't put a full tank of gas in my car since the end of February when Arco was the cheapest gas out there at $3.07. The only thing cheaper/or as cheep is CostCo's gas.
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  • 2 weeks later...
You're right! Mileage seemed to be getting worse for some time and performance became somewhat sluggish and sporadic. A/F Sensor was installed Thursday. Some 400+ miles later, all seems better and no codes thrown yet! At times, I think acceleration is sub par, other times it seems alright. So hopefully, this problem has been dealt with.

 

Side note: The local dealership readily told me I may be looking at a CAT replacement. They reset the code and told me if it came back, we'd be loking at replacng the converter. This forum saved me some unnecessary aggravation and $$$!

 

Did P0420 come back?

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Autozone did mine for free, and even gave me neat print outs with the explanation for the code(s).

 

 

Do they scan DTC codes as well? I'm getting an intermittent airbag code which I understand is a DTS code. I probobaly will have to check another thread.

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No codes to date! Actually, car seems to run very good right now. Have probably added some 800-1000 miles since replacement.

 

So you replaced only front and rear sensors with original cat to fix P0420, is that correct?

 

I changed my rear O2, P0420 came back but has not change front yet since I'm getting 28 MPG, just don't think it's the front O2 if I get such good MPG.

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So you replaced only front and rear sensors with original cat to fix P0420, is that correct?

 

I changed my rear O2, P0420 came back but has not change front yet since I'm getting 28 MPG, just don't think it's the front O2 if I get such good MPG.

 

I had misspoke earlier and was under the assumtion my mechanic had detected P0420. After checking myself, I learned it was P2097. My fuel economy was suffering, hovering around 22. Since changing out the front, I'm seeing 27. No codes have come back since.

 

Good luck!

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  • 2 years later...
I've replaced my car and both sensors and nothing has changed I still have my p420 code any ideas

 

Clear the code (if you have a scan tool or access to one) and drive the car for a week or three and see if it comes back. If it comes back, then there's a problem with the catalytic converters you bought or the rear o2 sensor is still having an issue. If all you're getting is the P0420, then you can bet it's the cats or downstream o2 sensor. The P0420 happens when the rear sensor gives readings that show the engine computer the cats aren't cleaning the exhaust good enough and it throws the P0420 code "catalysts below efficiency bank 1."

 

Check the wiring of the rear o2 sensor and make sure it's sound. Also check for exhaust leaks.

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