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Re: p0420
Posted to Technical Theory Forum on 10/19/2020 4 Replies

This is a CAT efficiency code and usually indicates the CAT is not doing its job. The O2 sensors are not seeing a change from the input to the output of the CAT. Did you use an aftermarket CAT? What are the actual reading from the O2 sensors?

Is there any ac... Login to read more.

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