Posted on Sep 14, 2012

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Auto zone gave me 2 code on my 03 gmc envoy po420 and po128

Working on 1 problem at a time.....looking to repair the 02 sensors first....where do i find the 02 sensor and how to repair it myself

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Stephen

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Posted on Sep 15, 2012

Stephen

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Well code 128 is for a faulty engine thermostat, usually the engine is not warming up to operating temp because the thermostat is stuck open.
Code 420 is for the catalytic converter not being up to acceptable performance on bank one which is the exhaust pipe for the side with cylinder one. Sometimes it means the cat is not working right, sometimes it is a problem between the front and rear O2 sensor, and sometimes it is something in the engine.
I would check the thermostat first and clear the codes to see if they come back.

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Auto zone gave me 2 code on my 03 gmc envoy po420 and po128

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Stephen

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Auto zone gave me 2 code on my 03 gmc envoy po420 and po128

1 Answer

Stephen

Add Your Answer

Attachments: Added items

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