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2003impala po420 code new cat and oxys - 2003 Chevrolet Impala

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Cheap converters can set 420 codes. down stream o2 did u change?

Posted on Sep 01, 2010

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Posted on Jan 02, 2017

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I eplace all o2 sensor and cat ,can not get rid of engine code po420


Well you have done everything. check wiring or replace the ECM. If you took this to a shop. Find another shop.

Aug 06, 2015 | Cars & Trucks

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Why am i getting engine code p0421 on this 2002 mitsubishi lancer?


this code is lazy cat (or weak or dead)420's are very hard to diagnose
here is the order.
1: NO EXHAUST leaks near any oxy sensor. zero, (cracks, or gaskets) any where near or upstream of any oxy sensor.!!!
2: Engine runs perfectly CEL out running and no stored or live DTCS (besides 421) and engine holds closed loop at hot idle and light flat cruise, steady right foot, if not , the CAT gets punished.
3: good front oxz sensors, a mUST.
4: AND 2nd last , new rear cat sensors (421s come from this sensor)
5: a NEW cat.

that is the crash course, can do 100s pages.
but no. just 1.

Jun 28, 2014 | 2002 Mitsubishi Lancer

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Code po420 on scan tool but o2 sensor was replace 2 months ago


Hello and welcome. the code P0420 is for a bad cat. converter. replacing 02 sensors wont repair this code. the code simply's means that thje cat. converter is not working as designed and will need to be replaced.

The PCM determines the oxygen storage capability of the catalytic converter has degraded below a calibrated threshold.

Jul 03, 2010 | 2004 Mazda RX-8

2 Answers

PO420 code-service engine light is on


P0420 Catalyst System Efficiency Below Threshold (Bank 1) first thing to do is go back to basics do a tune up (plugs) check the plug wires spray them with water or windex if you get a miss change them, run some fuel injector cleaner through it, don't just throw parts on it ,that is'nt cheap

Mar 24, 2010 | 2002 Nissan Altima

2 Answers

Check engine light on PO420 code ? recalls


Huge problems with these cars. The Pre-cat converter is built into the exhaust manifold. Expensive to replace. No Recall on this item. Some say that inferior compounds in the catalyst cause corrosion and early wear of the piston rings. I have seen one of these use 5 qts of oil in 300 miles. Is this car using excess oil?

Jan 16, 2010 | 2005 Nissan Altima

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I have a PO420 code. what are the possible problems?


THE CAT CONVERTOR HAS FAILED DUE TO A NUMBER OF ISSUES, OR THE SENSORS ARE READING WRONG CAN ONLY ANSWER WHEN HOOKED TO A DIAGNOSTIC READER TO TEST OUTPUTS FROM ALL RELATED COMPONANTS, IF U CHECK FOR FAULTS BEFORE YOU REPLACE CAT IT WILL SAVE YOU THE NEW CAT,

Dec 07, 2009 | 2000 Saturn SL

2 Answers

Fault code po420 ; is problem sensors or is it the cat conv


The only thing that will set this code is the catalytic converter or the oxygen sensor behind it. Way to tell if it is the sensor is to monitor voltage reading with scan tool and see if it is fluctuating the same as the upstream oxygen sensor. If it is the converter is "free flowing" and will have to be replaced. If the sensor is "flatlined" then it is most likely bad and setting the code.

Apr 30, 2009 | Ford Fusion Cars & Trucks

1 Answer

98 silverado codes po420,po430,po446


if the cat was pluggin you would see this as your going down the road it would not get to top speed .. They act up usually only run 40 top speed.

Apr 12, 2009 | 1999 Chevrolet Silverado 1500

1 Answer

The code PO420 came on for my 2000 Toyota Camray ......


Catalyst Effeciancy below threshold (Bank 1) is the code meaning. Check or replace the oxygen sensors. Some cars have 2 .One is on the front of the cat. the other is the on the back. Check the back sensor . Other possible causes are leaking or damaged exhaust manifold, bad coolant temp sensor.If toyota did not replace both . replace the one on the back of the Caty.

Feb 02, 2009 | 2003 Toyota Corolla

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