Question about Buick Regal

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I have 96 buick code p0420.I have replaced the converter and both 02 sensors.mil came back on code p0420. do not know what to do next, help.

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  • tyu960 Aug 02, 2008

    I have 96 buick regal. mil is on ,code p0420.I have replaced the cat converter and both 02 sensores.I have reset mil and it has come on agin.Dont know what to next.help.

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All Data On Line lists 5 different systems to check when a code of this nature is set.The first two items of course are the catalytic convertor itself,the O2 sensors,the fuel system,adequate flow and pressure and a good mist from the injectors,ignition and engine controls system,accurate and stable timing,sensors and solenoids,and the evaporative system.If any or a combination of the systems are malfunctioning,a catalyst efficiency code can be set.Catalyst efficiency is all about the O2 content after the convertor.If the engine is running richer than it should for any reason,or any malfunction of any of the involved systems,the cat convertor will not be able to do it's job fully,and a richer than desired exhaust gas is going to exit the tailpipe.So,a catalyst efficiency code is more about ALL of the involved systems relavent to,a well running,lean burning,engine.

Posted on Aug 02, 2008

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In some cases, a REFLASH of the engine computer may be required.

Brian

Keep us informed!

Posted on Aug 02, 2008

  • Brian Berndt
    Brian Berndt Aug 02, 2008

    This can be from overly sensitive catalyst montior.



    You should also check the entire exhaust system for leaks.

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To generate the P0420 DTC the 02 sensor is most likely working. On odb-ii cars the rear, post CAT convertor 02 sensor. It means your CAT has less than desireable oxygen storage capability. In most cases it is a bad CAT convertor. Hope that helps........

Posted on Aug 02, 2008

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Fault code that is set when the Onboard Diagnostic II (OBD II) system sees a drop in converter efficiency. The OBD II system monitors catalyst efficiency by comparing the switching activity of the upstream and downstream oxygen sensors in the exhaust. The upstream O2 sensor in the exhaust manifold reflects the condition of the exhaust gases as they exit the engine. The downstream O2 sensor in or behind the catalytic converter reflects the condition of the exhaust after it passes through he converter.

Posted on Aug 02, 2008

  • micromaster
    micromaster Aug 02, 2008

    Your Check Engine light is on and you find a P0420 code for a catalytic converter fault. Does that really mean your converter has reached the end of the road and needs to be replaced? A new converter can cost $600 to $1000 or more if a new car dealer or repair shop does the job, or maybe half that amount if you do it yourself. It's an expensive fix that may or may not be necessary. The problem, in most cases, is an emissions issue, not a performance issue that affects the way the engine runs.

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2 Answers

Where are the O2 sensors? I found one directly behing the spark plugs on the back.


The O2 sensor (2 on V engines) are in the exhaust system pipes before the catalytic converter, the next sensor is the efficiency monitor for the catalytic converter system it looks like a O2 sensor but performs a much different function as far as testing goes. The codes you have follow.

P0420 - Catalyst System Efficiency Below Threshold Bank 1
What does this mean? In most cases it means the catalytic converter is worn out and that is sensed by the catalyst monitor I spoke of earlier.

P0102 - Mass or Volume Air Flow Circuit Low Input
Faulty mass air flow sensor
- Dirty mass air flow sensor (located in the air intake hose to the engine from the air cleaner)
- Dirty air filter
- Mass air flow sensor harness is open or shorted
- Mass air flow sensor electrical circuit poor connection
- Intake air leaks

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this is a catalyst efficiency code meaning your cars computer has indicated a problem with the flow of your catalytic converter located just after the exaust manifold i the exaust system, usally these codes are triggerd by a bad or "lazy" oxygen or O2 sensor, try replacing your 02 sensors if they have some miles on them and this may cure the problem, after the repair you will need to have the check engine light cleared by a shop or auto parts store

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Catalist effeciency below threshold bank 1. This could be the catalitic converter or the 02 sensor behind the converter.

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#1 When you replace 02 sensors you should always replace all of them. Otherwise the new 02 sensor will be returning its Data back to the computer faster than the other old ones and this in itself may cause problems. #2 the P0420 indicates that the Catalysts System Efficiency is below the threshold on bank #1 And yes put in all new sensors and that means bank 1 sensor #2 as well. And then if the P0420 code returns replace the Catalatic converter on Bank#1.Please let me know the results. Good Luck and have a good XMASS.

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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

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1 Answer

P0420


There should be 2 O2 sensors. One is located before the catalytic converter and one downstream from the converter. I believe they should be right where the catalytic converter is.

I hope this helps! :) Let me know if you need any further assistance in this matter.

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Receiving engine code p0420 on my 2005 altima 2.5 s


A p0420 code indicates a Catalytic System efficiency failure, Bank 1.
Basically, the computer is seeing reduced efficiency of the catalytic converter or one of it's components (such as an 02 sensor)

There may be a few root causes, such as a faulty oxygen sensor, faulty coolant temperature sensor, faulty converter, Large exhaust leak, or retarded (slow) timing.

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2002 Buick Century Code P0420


Sounds as if yoou are actually having a fuel system problem.You need to rreplace the fuel filter and then check the fuel pressure. You should have around 50 psi. If the fuel filter stops up it will cause the exhast to starve for fuel and can damage a catalyst converter. You can get the fuel filter for about 15 dollars at any local parts house.

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Code P0420


P0420 Catalyst System Efficiency Below Threshold (Bank 1)

There is one 02 sensor in front of the catalytic converter (called upstream), and one behind it (downstream). When the engine is warmed up and running normally the upstream oxygen sensor reading fluctuates and the downstream one is fairly steady. In the case where both readings are fairly steady, a P0420 check engine light code is set.

Possible Causes:
Oxygen (O2) sensor not working correctly
Damaged or leaking exhuast (pipe, manifold, catalytic converter)
Damaged catalytic converter

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