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Q: P0420 code

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I noticed a few months ago my check engine light would go on and off. Now it stays on and I was told it won't pass smog. The code is p0420 "b1 cat system system below threshold."

I am curious to see if I can fix this problem or pass smog in ca without replacing. Also my spark plugs are in need of replacing I believe could that affect the codes? What would be your course of action if you need to pass smog with this code

My car has 171000 miles.
My car has an automatic transmission.

A: Hi there: That’s a very tricky question to...

Hi there:

That’s a very tricky question to answer. In general, the P-0420 OBD-II error code indicates that there is a reduction of efficiency of the catalytic system for reducing emissions. This could be caused by O2 sensors, leaking fuel injectors, problems with the EGR system or the catalytic converter itself. Depending on which state you live, would dictate my corrective course of action as each US state has different emissions standards for passing. You might want to have one of our professional mechanic in your state complete a check engine light is on inspection; which will allow them to dig deeper in the ECU to see what specifically triggered this error code.

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