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1997 Monte Carlo-3.1 P0420 need to pass emissions, help!
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VPdan21
Novice
Sep 6, 2011, 7:00 PM
Post #1 of 7
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1997 Monte Carlo-3.1 P0420 need to pass emissions, help!
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1997 Chevy Monte Carlo with a 3.1
P0420 continues to pop on once car is driven for awhile. Replaced PCV, EGR and damaged rubber grommet by throttle body. After replacing the grommet, the CEL seemed to stay off a little longer. Coincidence maybe. After about a week of no light, P0420 came back up. Local mechanic said "bunch of vacuum leaks, not worth fixing". This was after he doused with carb cleaner. I don't think this is correct. I am trying to avoid getting a cat, but a lot of people are pointing me in that direction. No dents or damage on the outside. O2 sensors and wiring look fine. Scanner does show both sensors running at similar levels. Anything anyone has seen in their experiences that would point the problem towards something else? Please? haha thanks.
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Discretesignals
Ultimate Carjunky
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Sep 6, 2011, 7:12 PM
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Re: 1997 Monte Carlo-3.1 P0420 need to pass emissions, help!
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NOTE: You have to make absolute sure that you don't have any other driveability problems before taking a cat code into account. That means the engine can be misfiring, running lean, backfiring, burning oil/coolant, overheating, running rich, or has PCM updates concerning cat testing sensitivity before suspecting a faulty cat.
If all that is good and your trims are normal, that is when you go after P0420.
P0420 is a cat code. Means the cat has become inefficient at cleaning the exhaust. If your rear O2 sensor's voltage signal mimics your front O2 sensor's voltage signal with the engine at operating temperature and the engine around 2000 rpm, your cat is trash.
Bad cat waveform pattern:
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
(This post was edited by Discretesignals on Sep 6, 2011, 7:13 PM)
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Hammer Time
Ultimate Carjunky
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Sep 6, 2011, 7:12 PM
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Re: 1997 Monte Carlo-3.1 P0420 need to pass emissions, help!
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I don't know what you threw all those parts at it for. The PO420 is pretty clearly just a bad cat. You won't see any other indications. It's just not doing it's job chemically.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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VPdan21
Novice
Sep 6, 2011, 7:28 PM
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Re: 1997 Monte Carlo-3.1 P0420 need to pass emissions, help!
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Thanks for the help guys. Sensors are definitely acting that way. I DID have a P0401 as well which is why I changed the EGR in the first place. That and some wishful thinking I guess, dont want to replace the cat. Thanks again, didnt know that code was so specifically just the cat.
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Discretesignals
Ultimate Carjunky
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Sep 6, 2011, 7:37 PM
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Re: 1997 Monte Carlo-3.1 P0420 need to pass emissions, help!
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Did you clean the ERG port out with a coat hanger and some carb cleaner in the upper intake. A clogged EGR port usually sets P0401 on an M engine. If the port is clogged, you'll be seeing that code again.
Before:
After:
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
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VPdan21
Novice
Sep 6, 2011, 7:42 PM
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Re: 1997 Monte Carlo-3.1 P0420 need to pass emissions, help!
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That was going to be my next course of action thinking maybe that was throwin both codes, but I think I am delaying the inevitable which is replacing the cat.
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Hammer Time
Ultimate Carjunky
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Sep 7, 2011, 3:03 AM
Post #7 of 7
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Re: 1997 Monte Carlo-3.1 P0420 need to pass emissions, help!
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It isn't that big a deal. You can have an aftermarket installed for around $200 on most cars.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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