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