Question about 1996 GMC Sierra

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I changed the plugs and plug wires on my 96 GMC Sierra SLE 5.7L yesterday. Now my OBD scanner shows catalyst and EGR test as not completed or failed. No actual codes. When I first ran the scanner a couple of weeks ago, it showed no failures, no codes. Did I screw something up?

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It can be possible that catalyst converter and egr were going weak and got faulty.But this does not necessarily mean the Catalytic Converter is bad!. Either Converter operating below efficency or Converter operating below threshold. No where in the interpretation of that code does it say the converter is bad. Your vehicle may very well need a Catalytic Converter but to determine this, First the egr valve and converter needs to be removed and properly cleaned.A dirty converter or clogged converter with carbon build up can cause it.Look at the O2 sensor output signals. Sensor 1 is before the converter, Sensor 2 is behind the converter, the dirty 02 sensor can also cause this problem. Also check the gas cap, if its loose then re-tighten it ,if its worn out , it has to be replaced.This possibilities are to be checked, before actually replacing catalytic converter and egr valve.Most probably its dirt valve and converter causing this.------------- This should help.Thanks,.Helpmech.

Posted on Mar 17, 2011

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Posted on Jan 02, 2017

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