P0420

[Chris]

Wiring, o2 sensors, injectors, or cats? Where do I start?

 

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[tesnoboy]

How many miles on it? Have you reset it to see if the code comes back? If you have, I would try the rear O2 sensor on that bank 1.

[BlackZ71Silverado]

Wiring, o2 sensors, injectors, or cats? Where do I start?

 

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Double topic.......

 

http://www.gm-trucks.com/forums/index.php?showtopic=145464

[Chris]

i cleared the code. came back. does run a bit rough. i can feel it being less responsive.

 

and that first topic was before i knew the code just knew a possibility

[BlackZ71Silverado]

Sorry but you posted the code, here it is from the first topic:

 

"P0420 is the code. Says catalyst system efficiency below threshold bank 1".... also more information in the first one for people to read and get the whole story.

 

Did you have the sensor tested?

[Chris]

Yea at first. I did that at a stoplight. But how do you test the sensor? And upstream or down?

 

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[txab]

The code is for the downstream sensor, past the cat

[Chris]

The code popped for the cat. It was changed old one was in pieces on the inside. Code is gone now

 

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