1998 Chevy Malibu P0420, P0420pd

Tiny
BKSFLYESTPAPI333
  • MEMBER
  • 1998 CHEVROLET MALIBU
  • 6 CYL
  • FWD
  • AUTOMATIC
  • 101,000 MILES
I have already replaced the catalytic converter and I still have the same code coming up with the check engine light. What could the problem be?
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Tuesday, March 17th, 2009 AT 6:50 AM

12 Replies

Tiny
DOCFIXIT
  • EXPERT
Possible causes for code p0420
Leak in exhaust before cat
HO2S circuit damage check wiring and O2 tight
was cat replaced with OEM?
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Tuesday, March 17th, 2009 AT 11:05 AM
Tiny
BKSFLYESTPAPI333
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The cat was replaced by meineke. I'm not sure if they use OEM, I don't think so though.
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Tuesday, March 17th, 2009 AT 11:16 AM
Tiny
DOCFIXIT
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If not GM part code will reset have run into this numerous times
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Tuesday, March 17th, 2009 AT 11:46 AM
Tiny
BKSFLYESTPAPI333
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So it is possible that everything is working fine and the code is just coming up because it's not a GM part? So to be safe I would have to check everything else anyway just to make sure?
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Tuesday, March 17th, 2009 AT 11:47 AM
Tiny
DOCFIXIT
  • EXPERT
Did light stay off for a while after cat replaced?
Having the car diagnosticaly scanned would clear up what is going on.
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Tuesday, March 17th, 2009 AT 11:53 AM
Tiny
BKSFLYESTPAPI333
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The light was off for about a week after the cat was replaced. Then it came on and I scanned it with my Actron PocketScan Plus OBD II Code Reader. It came up with P0420, P0420pd. I brought the car back to meinek and they scanned it with their Code reader and said it was probably the O2 Sensor. He erased the code to see if it would come back and it has.
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Tuesday, March 17th, 2009 AT 11:57 AM
Tiny
DOCFIXIT
  • EXPERT
Then PCM is seeing a low efficiency in cat. It takes several reads for code to set so reset of PCM works for a while. Did Meniek diagnose the cat replacement?
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Tuesday, March 17th, 2009 AT 12:03 PM
Tiny
BKSFLYESTPAPI333
  • MEMBER
Well, when I went to meineke and told them the code I was getting, they lifted the car up, looked at the cat and said the cat needs to be changed. They plugged their code reader and got the same code and still said to change the cat. They didn't test or thoroughly check anything.
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Tuesday, March 17th, 2009 AT 12:17 PM
Tiny
DOCFIXIT
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Does not sound like they did. Cats don't go bad that often for your mileage and they go when thereis an engine miss, injector leaking. You have an O2 in front and one after Cat the PCM compares the two readings. If it does not see the right results it set a code. An exhaust leak or O2 will cause code. A scan of PCM by a qualified Tech would show fault.
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Tuesday, March 17th, 2009 AT 12:28 PM
Tiny
BKSFLYESTPAPI333
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Well I will admit that the cat might have been bad because I had a misfire on cylinder three for a while which eventually caused a multiple misfire on two cylinders. The misfire was going on for about a year. I know it's a long time but these mechanics can be so full of themselves around here where I live so I dont trust them too much. But even if the cat was bad, there is obviously something else wrong for the code to continue to pop up. By "scan of PCM", you mean a diagnostic test?
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Tuesday, March 17th, 2009 AT 12:32 PM
Tiny
DOCFIXIT
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Yes they will read the outputs of the O2 s and other sensors to determine why code is setting. Ask around try fine an A.S.E. Certified shop but keep in mind a non GM cat will cause the code
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Tuesday, March 17th, 2009 AT 1:53 PM
Tiny
BKSFLYESTPAPI333
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Ok so the code might just be because of the non GM cat? Does the non GM cat work just as good as a GM cat?
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Tuesday, March 17th, 2009 AT 3:12 PM

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