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service engine soon code P4020


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roc0999's Avatar
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May 26th, 2009, 7:24 PM   #1  
service engine soon code P4020

HELP! with this one I have no clue as to what its talking about

 
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May 26th, 2009, 8:03 PM   #2  
Do you mean p0420? If you do it means Catylyst system efficiency below threshold. I hope thats what you meant and this helps. If this was it I would say replace your Cat converter.

 
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May 26th, 2009, 8:17 PM   #3  
or....


A code P0420 may mean that one or more of the following has happened:
  • Leaded fuel was used where unleaded was called for
  • An oxygen sensor is not reading (functioning) properly
  • The temperature sensor is not working properly
  • Damaged or leaking / catalytic converter / exhaust pipe
  • Retarded spark timing
  • The oxygen sensors in front and behind the converter are reporting too similar of readings
Possible Solutions


Some suggested steps for troubleshooting a P0420 code include:
  • Check for exhaust leaks at the manifold, pipes, catalytic converter. Repair as required.
  • Use a scope to diagnose the oxygen sensor operation (Tip: The oxygen sensor in front of the catalytic converter normally has a fluctuating waveform. The waveform of the sensor behind the converter should be more steady).
  • Inspect the downstream heated oxygen sensor (HO2), replace if necessary
  • Replace the catalytic converter
One thing to note is that many offer a longer warranty on emissions-related parts. So if you have a newer but it's out of it's bumper-to-bumper warranty, there still may be warranty on this type of problem. Many manufacturers give a five year, unlimited mileage warranty on these items. It's worth checking into.

 
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May 27th, 2009, 4:51 PM   #4  
yes that was the code, looks like I have my work cut out for me on this one

 
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May 28th, 2009, 4:56 AM   #5  
will do

 
roc0999's Avatar
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May 31st, 2009, 4:17 PM   #6  
where is the best place to get good prices on cat's for 99 4.3 ASTRO?

 
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May 31st, 2009, 4:21 PM   #7  
I have had good luck with getting items thru 1aauto

http://www.1aauto.com/1A/CatalyticCo...hevrolet/Astro

 
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May 31st, 2009, 5:29 PM   #8  
they're a little on the expensive side , 346.00, I seen them for 285.00 w/free shipping thanks for the input though

 
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May 31st, 2009, 9:19 PM   #9  
OE cat converters have a mandatory 8 year 80,000 mile warranty from the factory. 99.9% of the time a catalyst efficiency code is a bad cat. You need to be careful some cars have more than one cat. The one the light is referring to has to have a o2 sensor before it and after it.

 
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May 31st, 2009, 10:09 PM   #10  
I have also seen this code be set with an aftermarket O2 sensor POST cat.
Had a customer with a dead O2 sensor, replaced it with a bosch sensor, and they came back the next day with this code. The O2 readings, instead of being dead, it would switch too fast. The post cat O2's are designed to be "lazy". Switched it out with a Delco and never saw it back

 
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