Question about 1996 Lexus LS 400
P0420 is "catalyst system below efficiency". It means that the car thinks a catalytic converter is bad. It could be that the cat is failing, but it also may be that the secondary oxygen sensor (behind the cat, used as a comparator to determine the health of the cat) is failing. As that part is about 10% of the cost of a new catalyst, I'd replace it first, have the code cleared, and see if it comes back.
Posted on Dec 09, 2009
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Posted on Jan 02, 2017
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