Question about 2001 Chevrolet Impala

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I failed my emissions test the first time due to codes P0420. I had a new catyctic converter put on and took my car back for a second test and it was rejected. They told me that it was because my system has not reset itself. How long does it take for my system to reset? How many miles? I have a chevy Impala 2001

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Reset the system yourself. 1st do you have to insert a code into the stereo if your battery is dead? if not,then disconnect the positive cable from your cars battery for 10 minutes,this will reset the cars computer system.you may have to reset your radio and personal comfort codes again,but this should be what you need to pass the test. thank you for choosing fixya.com

Posted on Mar 30, 2011

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You need to drive it through a complete drive cycle from a cold engine all the way to it getting the car to operating temperature and driving both city and highway driving with the usual stop and go driving without turning the car off as when this happens the drive cycle starts all over again.some systems may need more than one drive cycle to relearn a cycle and you won`t have to do the long drive cycle but make the first one the long drive.

Posted on Mar 30, 2011

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P0420....Catalyst System Efficiency Below Threshold (Bank 1)

i think one of the O2 sensors isnt working ,now they can be tested with a automotive multimeter but you would need basic knowledge to be able to do this so i would advise you ask a local mechanic to test them for you ,you do not need a code reader to diagnose any electrical fault on a motor vehicle only a meter ,its the only way i can diagnose anything on europeon market vehicle especially from 2005 as the software is all encrypted ,in europe they put a probe up the exhaust and run engine at 2500 rpm try plugging the OBDII in and a lot of cars will lock up with the immobilisor .

Posted on Mar 30, 2011

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I have two codes come up when checking why my check engine light is on. P0447 and P0420. Any info on what these mean and what it takes to fix so I can pass my smog test??


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Definition of P0420 is catalyst below threshold. This is indicative of (among other things) a converter that is not working as efficiently as it should be (according to specs). Catalytic converters are not normally a "wear" type item, that is they are not deisgned to wear out and need replacement. If they have failed, it is likely due to something else that caused it to fail.

P0447 Evaporative Emission Control System Vent Valve/Solenoid Circuit Open. The Powertrain Control Module (PCM) has detected an open within the circuit that controls the vent valve or solenoid for evaporative emission systems vapor.

Read more at: http://www.obd-codes.com/p0447
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Jan 26, 2016 | Hyundai Motor 2002 Elantra

1 Answer

Ford obd error code p0420


clogged catalytic converter, replace it with a new one, or remove old one, use a long pipe and punch a hole through it, empty out the pieces, and reinstall. That will work if you don't get the sniffer stuck on your exhaust during emissions testing, as your emissions will be very high using my pipe through the converter method.

Dec 16, 2013 | Ford E-350 Super Duty Cars & Trucks

1 Answer

Replaced catalyst converter, both sensors and still have code P0420 what's the problem


Hi there:
The possible causes of this code are: exhaust leak between the exhaust manifold and converter, downstream O2 sensor wiring damaged due to coming in contact with exhaust pipe, or failed converter.


Check for any exhaust leaks and repair as necessary. Check wiring harness at O2 sensor and if damaged repair or replace. Keep in mind that catalytic converter have a 8yr/80,000 mile federal emissions warranty, so if you have less than 80,000 miles this will be covered undered the warranty and would need to be replaced by dealership.


We strongly recommend that if you need to replace the catalytic converter that you replace it with an OEM unit. Second choice would be a high-quality replacement part. There are many stories in our forums where folks replaced the cat with a cheaper aftermarket one only to have the code return shortly thereafter.



Hope this helps; also keep in mind that your feedback is important and I`ll appreciate your time and consideration if you leave some testimonial comment about this answer.

Thank you for using FixYa, have a nice day.

Aug 24, 2012 | 2002 Honda Civic

1 Answer

Check engine with code p0420


Generally, this code is from a failed converter. Most exhaust or diagnostic shops can perform a converter back pressure test to confirm if the converter is failing.


DTC P0420 - Catalyst System Efficiency Below Threshold (Bank 1)
The catalytic converter has an oxygen sensor in front and behind it. When the vehicle is warm and running in closed loop mode, the upstream oxygen sensor waveform reading should fluctuate. The downstream O2 sensor reading should be fairly steady. Typically the P0420 code triggers the Check Engine Light if the readings of the two sensors are similar.


This is indicative of (among other things) a converter that is not working as efficiently as it should be (according to specs). It is part of the vehicle emissions system.

Some suggested steps for troubleshooting a P0420 error 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 (HO2S), replace if necessary
  • Replace the catalytic converter

Overall probably the biggest mistake vehicles owners make when they have a P0420 code is to simply replace an oxygen sensor (H02S). It is important to do proper diagnosis so you're not wasting money replacing parts unnecessarily.

We strongly recommend that if you need to replace the catalytic converter that you replace it with an OEM unit. Second choice would be a high-quality replacement part. There are many stories in our forums where folks replaced the cat with a cheaper aftermarket one only to have the code return shortly thereafter.

One thing to note is that many vehicle manufacturers offer a longer warranty on emissions-related parts. So if you have a newer car 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.


Hope this helps; also keep in mind that your feedback is important and I`ll appreciate your time and consideration if you leave some testimonial comment about this answer.

Thank you for using FixYa, have a nice day.

Jun 22, 2012 | 2002 Chevrolet Impala

1 Answer

My 2000 Toyo. Tacoma Prerunner TRD V6, truck Failed smog due to the part #3 Functional Computer Tests due to an erased MIL. But had passed the Visual Inspection, and Emissions. So i bought a Code reader...


there are 2 sensors in the system
one is a heated oxygen sensor (HO2S) in the exhaust manifold / pipe before the cat converter that reports the exhaust gas composition to the ECM so that fuel/ air ratios can be adjusted
if that one is faulty it is most likely the reason for running lean or rich
the second sensor is the oxygen sensor (O2) which is after the cat converter and reads the results of the cat converter cleaning the exhaust
you may have to replace both the sensors to get a clearance or replace the cat converter as well as the HO2S unit

Jun 02, 2017 | 2000 Toyota Tacoma PreRunner

1 Answer

I have a 2006 Pontiac G6; 4 cylinder...the check engine light is on and I need to get it off for my emissions test so I need help finding out what the problem is. Ive had the car put on the scanner twice...


when you changed the parts did you have the codes cleared ? as if the comp stored it then it will return and when you put new parts on it took the comp time to test and display new changes.

Jan 19, 2011 | 2006 Pontiac G6

2 Answers

Auto Zone run a diagnostic test on my truck and they got a troubleshooting code of P0420-catalytic converter defective possibly due to engine misfire or running condition, large vacuum leak, engine oil...


To keep it inexpensive i would actually try to change the downstream and upstream o2 sensors first one at a time and see if the code goes away.

Dec 23, 2010 | 1996 Chevrolet K1500

1 Answer

Check engine light on. took the car to auto zone to put it on a scanner. trouble code p0420. catalyst system efficiency below threshold. probable cause; large vaccum leak, fuel system fault, ignition...


Diagnostic code produces P0420 catalyst system efficiency below threshold-Bank 1. Probable causes are listed as follows:
1-air leak in exhaust before rear 02 sensor, 3-Fuel system fault,
4-faulty catalytic converter.

May 31, 2010 | 2001 Nissan Altima

3 Answers

Code p0420


Repair information for the OBD-II trouble code P0420 - Catalyst System Efficiency Below Threshold (Bank 1) Probably needs a catalytic converter

Apr 06, 2010 | 1999 Ford Contour

1 Answer

07 caliber p0420


Might still be under warranty. P0420 is a catalytic converter efficiency code. Usually this means the catalytic converter is no longer able to do it's job. The computer knows when it is failing and sets this code.

Check with your dealer to see if the catalytic converter might still be covered as it is an emissions component.

Feb 14, 2009 | 2007 Dodge Caliber SXT Sport Hatchback

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