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P0420 G mil or Pend - 2006 Chevrolet Malibu

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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.


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.

Aug 02, 2008 | Buick Regal Cars & Trucks

1 Answer

What is fault code P0420


P0420 OBD-II Trouble Code Technical Description Catalyst System Efficiency Below Threshold (Bank 1) What does that mean? This diagnostic trouble code (DTC) is a generic powertrain code. It is considered generic because it applies to all makes and models of vehicles (1996-newer), although specific repair steps may be slightly different depending on the model. So this engine code article applies to Nissan, Toyota, Ford, GM, etc. The catalytic converter is a part of the exhaust system that looks kind of like a muffler, although it's job is very different from that of a muffler. A catalytic converter's job is to reduce emmissions from the exhaust. 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). 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. Symptoms The main symptom to the driver is the illumination of the MIL (malfunction indicator lamp). You will likely not notice any drivability problems, although there may be symptoms. For example, if the substance inside the catalytic converter is broken or failed, it may be restricting the exhaust which will result in a feeling of reduced power output from the vehicle. Causes A code P0420 may mean that one or more of the following has happened: Leaded fuel was used where unleaded was called for A damaged or failed oxygen sensor (HO2S) Downstream oxygen sensor (HO2S) wiring damaged or connected improperly The engine coolant temperature sensor is not working properly Damaged or leaking exhaust manifold / catalytic converter / muffler / exhaust pipe Retarded spark timing The oxygen sensors in front and behind the converter are reporting too similar of readings Leaking fuel injector or high fuel pressure Cylinder misfire Oil contamination Possible Solutions 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.

Read more at: http://www.obd-codes.com/p0420
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Jun 18, 2014 | 1996 Subaru Impreza

1 Answer

TROUBLE CODE P0420


P0420 isnt a misfiring code; this code P0420 is refer at Catalyst System Efficiency Below Threshold (Bank 1).

Feel free to contact us if you need additional details to volve it clicking the link.

Oct 24, 2011 | 2002 Volvo S60

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

Mil bulb not work .conector damage.mil commando on code # p0420.p0401.p0740


P0420 = catalyst system efficiency below threshold (bank 1).

P0401 = Exhaust gas recirculation-insufficient flow detected

P0740 = Torque converter clutch, circuit malfunction.

Mar 07, 2011 | Honda Odyssey Cars & Trucks

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

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.

Feb 20, 2010 | 2002 Saturn L-Series

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