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P0420 error engine light is on

Went on a road trip from Atlanta to Nashville. 75 miles into the trip , the check engine light came on. I drove it for the rest of the weekend. There were no apparent signs of engine failure. I took it to the local Auto Zone for a diagnostic test and a P0420 error code came up. I'm hoping it's a minor problem . I've seen everything from replacing the catalytic convertor to changing out a simple cat sensor. Where to begin?

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  • Michael Fermil Nov 30, 2012

    I spoke to friend who had the same problem (P0420 error code) he said to disconnect the battery for 30 seconds. So far, so good. No check engine light after 30 miles ..

  • montehammons Nov 30, 2012

    goood! maybe it was a ghost code, a glitch.

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  • Cars & Trucks Master
  • 5,341 Answers

One or the other. Before I would change out a catalytic converter, I would want the old one tested first to make sure it is bad. Or you might just try a new oxygen sensor on bank 1. Bank 1 would be the driver's side, or whatever side of engine has the number one cylinder-that is bank 1.
P0420: catalyst system efficiency below threshold (Bank 1).

Posted on Nov 29, 2012

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Posted on Jan 02, 2017

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SOURCE: check engine!

normally you need to change the converter if you have smog test you have no choise if not disconnect the battery for a minute and try it out hopefully it will not come back hope its a fixya thanks for the post pierre

Posted on Jul 31, 2008

  • 295 Answers

SOURCE: 1999 Honda Odyssey p0420 Error Code

Cat efficentcy. replace the converter.

Posted on Jul 07, 2009

pal03246
  • 726 Answers

SOURCE: Nissan Sentra 2001 gxe with code p0420

You will need a new catalytic convertor assembly. Yours is below treshold efficiency in other words its "no good".If you have it replaced, ask the garage/dealer to give you the old one back. Its worth some cash if its full. It doesn't matter thet it failed. They are going after the mesh inside of it and that is worth some $$$$. May not be much , but better than nothing.

Posted on Jul 26, 2009

Rebgagnon
  • 382 Answers

SOURCE: 2000 Subaru Outback Wagon (100K miles) with P0420 Code

I do not know for sure if this is the problem you are having, But, I have noticed that from 95 up to 2002 I have seen a lot of PO420 codes that have been just the sensor. I do not know if it was a weak sensor or just that program telling it that it is below threshold. I did notice that if the vehicles are run for a long trip at highway speed it goes out. I wish you luck and have a great day.

Posted on Feb 11, 2010

  • 67 Answers

SOURCE: 2001 Honda - New Catalytics & O2 sensors -- new 0420/1739/1456

I would send the car for a smoke test for the emissions leak...Find out where the leak is comming from..Repair it..Reset the codes, then do a drive cycle and see what happens...

Posted on Feb 19, 2010

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