Engine Code P0420 On 1997 Chevy Blazer,(catalyst System Below Threshold On Bank1). What All Can Cause This Code?


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Ramsey Maness Profile
Ramsey Maness answered
   Essentially this code is relaying a fault detected by an Oxygen sensor. Bank 1 - the one in front of the  Catalytic Convertor, Bank 2 - behind the Convertor. So, should you replace the sensor? NO - not yet. Should I replace the Catalytic Convertor? NO - not yet.
   You must try to untangle the web of potential problems first. Usually on lower mileage vehicles an Oxygen sensor can be the culprit. On older - high mileage cars, a Convertor may likely be the source of that irritating light on your dash. Suggestions:
 1 - Examine the Oxygen Sensors connections and wiring. Ensure all is well.
  2 - Inspect the Sensors closely. If corroded but otherwise intact in appearence - then while they   
  may have set off the alarm, something else may be corroding them.
    3 - Check the convertor. Determine the back/exhaust pressure levels and tolerances. A clogged or
  failing convertor usually results in less back pressure and more between it and the engine.
      4 - Get ready to be frustrated. You may replace both sensors and a convertor only to find it
  starts all over again several thousand miles later. 
  5 - Point is:  begin examining compnents of the engine that may cause sub-specified exhaust
  gases - EGR, FI problems, valve timing, igintion timing. - the list goes on till frustraions
  earlier light.

Good Luck.

Ramsey Maness -

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