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International Automotive Technicians Network
Re: GM dealer says P0420 caused by downstream sensor. What say you?
Posted to Technical Discussion Forum on 3/11/2007

[...trimmed text...]

I agree it's not likely, but it can happen. Here's a theory that doesn't blame the sensor element...

Think about the four wires where they enter the sensor base. Think about the angle you often see ... Login to read more.