Question about 2003 Chevrolet S-10

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PO420 CODE ON CHEVY S10

IM GETTING THE PO420 CODE ON MY 2003 4.3L V6 CHEVY S-10, I RECENTLY CHANGED OUT THE CATALYTIC CONVERTER, A COUPLE WEEKS LATER MY SERVICE ENGINE SOON LIGHT CAME ON. SINCE THEN I HAVE PUT IN NEW AIR FILTER, SPARK PLUGS, SPARK PLUG WIRES, I ADDED A BOTTLE OF GUMMOUT FUEL SYSTEM CLEANER TO THE GAS TANK, ALSO HAVE DONE AN OIL CHANGE,THE LIGHT IS STILL ON!! ANY HELP/SUGGESTIONS WILL HELP
THANKS FOR HELP
OSCAR

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  • 2 more comments 
  • perezoscarop Mar 01, 2009

    HOW MANY OXYGEN SENSORS DOES MY TRUCK HAVE?AND WHICH ONE IS AT FAULT?
    I HAVE DISCONNECTED THE BATTERY ALREADY, DIDNT WORK


  • perezoscarop Mar 01, 2009

    WHERE CAN I FIND THE ELECTRICAL TERMINALS FOR THE INJECTORS??

  • perezoscarop Mar 03, 2009

    WHAT DOES PCM STAND FOR?

  • Anonymous Apr 17, 2009

    i have a 2001 s10 2.2 with the same code. i am being told to flash the computer the parimeter is too small, its running too rich because the computer thinks the engine is always cold, and some other things. i replaced the conveter and o2 sensors twice! i am taking it in for a total engine diagnosis tomorrow, not a scanner. the scanner says the converter is bad!!! if so, why the running rich????????

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Hi

The code means---

Catalyst Efficiency
Below Threshold
(Bank 1)

Please make sure there is no air entering the engine behind the maf, such as a vacuum leak or leaks in ducting between the maf and the throttle body.

If that's no the case then its an issue with injectors clogging and they are not working due to "fretting". This "fretting" is electrical terminals to injectors getting oxidation on them and is fixed by unplugging them and replugging them in. The fix is to put a small dab of die-electric grease on the terminals.

I would suggest an injector service with the new GM procedure using "Top Engine Cleaner". This may be all you need but that P0420 bothers me. P0420, Catalyst System Efficiency Below Threshold, can be set by a poor connection at the PCM or a damaged wiring harness.

Please rate this soluton as FixYa if found useful.

Thanks
Rylee

Posted on Mar 01, 2009

  • Rylee Smith
    Rylee Smith Mar 05, 2009

    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 (HO2), replace if necessary



    Replace the catalytic converter if the error still doesn't go.



    Please revert for further clarifications.



    Thanks

    Rylee

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I have a 2000 chevy s 10 4.3 4wd that ran good then it started hesitating like it has no power , after warming up and trying to go more than 25 pmh, checked plugs , wires, distrib all seems good any ideas???

Posted on Dec 23, 2012

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The codes must be cleared with a scan tool. Oxygen sensor is the fault code, replace and clear ECU with scan tool, or by disconnecting the battery for a while

Posted on Mar 01, 2009

  • Patrick Cowan
    Patrick Cowan Mar 03, 2009

    Programmed Control Module

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for the code po420, you need to patch the leak first then clear the code and dirve the car one or two days to see the code come back on, if not you just fix the problem. but I bet it is your catalytic converter is bad, the rattle sound is not coming from the engine, it is from the catalytic converter, use a seth pole to listen, the catalytic converter is right infront and it is part of the exhaust mainfold.

Good luck.

Oct 02, 2014 | 1996 Toyota Camry

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Getting a engine code PO420.My code book says Catalyst efficiency below threshold(bank1).What does that mean I HAVE TO DO TO FIX THE PROBLEM.i


Hi, the usual cause is a worn out catalytic converter, but this code may also set due to a rich mixture. Check your tailpipe for soot or black film. If the pipe looks OK, replace the catalytic converter. If your converter is recently replaced or you have soot, please get back to me for a different plan of action.

May 08, 2011 | Honda Odyssey Cars & Trucks

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Im trying to get my mother in laws 2006 chevy equinox to pass emissions the codes po171 and po420 keep coming up po171 is lean bank one and po420 is catalyst below efficency im trying to narrow it down to...


For the lean condition I wound look for vacuum leaks.I you don`t find any then replace the o2 sensor for bank 1.As for the po420 if the exhaust system is not bent or damaged you will have to replace the catalytic converter.The catalytic converter has a longer warranty then the regular vehicle warranty itself so call the dealership and find out if the converter is still under warranty.The usual warranty I believe is around 80k.mileage years is 7 or 8 not positive.Hope this helps.Good luck.

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Po420 code monte carlo ls 2001


PO420 code is for catalyst system efficiency below threshold (bank 1) Usually it means that it is time for a new catalytic converter on bank number 1. Cylinder bank number 1 is always the bank with the number 1 spark plug in it.

Apr 20, 2010 | 2001 Chevrolet Monte Carlo

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What is an code po300 and po420 and what do i need to do i have an 2002 nissan altima


The p0300 code is a random missfire code sometimes caused by bad spark plugs and wires, if you have not done a tune up, it's time for one. now, the p0420 code is for catalyst efficiency below threshold, basically, your catalytic converter is bad and may need to be replaced. Sometimes repairing the random missfire can eventually clear the p0420 code. your car is not burning fuel properly, therefore the catalytic converter is getting dirty. Also, if you notice blue smoke coming out the tail pipe, then that's the cause for a failing catalytic converter as oil is getting to the combustion chamber and being burned off through the exhaust.

Mar 09, 2010 | 2002 Nissan Altima

1 Answer

PO420


Not just a faulty catalytic converter will trigger this code. Many other issues can trigger this code.

  • Leaded fuel was used where unleaded was called for
  • An oxygen sensor is not reading (functioning) properly
  • The engine coolant temperature sensor is not working properly
  • Damaged or leaking exhaust manifold / catalytic converter / exhaust pipe
  • Delayed spark timing
  • The oxygen sensors in front and behind the converter are reporting too similar of readings
Possible solutions:
  • Check for exhaust leaks at the manifold, pipes, catalytic converter.
  • Replace Coolant Temperature Sensor
  • 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 (HO2)
  • Replace the catalytic converter
  • Have timing adjusted


Aug 25, 2009 | 2002 Toyota Camry

1 Answer

Check engine light on.


the problem is with the catalytic converter, there is a specific emission threshold that the exhaust must maintained. when it falls below this, you get this code. i just had to replace my converter for the same problem

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