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2003 Rx300, 75000Miles


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Have had this vehicle for a little over a year, 2 days ago the CEL and VSC lights came on, Auto Zone scan shows P0420 code,Catalyst efficiency below threshold bank 1. Any ideas where I should start looking, I guess this thing has a "Warm-up converter" downstream of each bank so maybe it is simply a bad sensor?

One more note to add, when we first attached the Scan Tool it could not communicate with the on-board diagnostics, turned out the 7.5 amp fuse for the OBD was blown, any ideas? So far am not having any drive-ability issues.

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Two pieces of advice. You may or may not want to take them but they are good advice and free. I know you can get the codes read for free, but at the cheap price that you can buy code readers (and even ones that give you some elementry information), no one but old ladies should be without one. That way you can read and cancel without leaving your driveway. I bought one at Costco when they were closing then out, for $19., and then returned it the next day because I have a $700. scanner and wondered why I bought it, no matter how good the deal. It was actually a small but nice scanner/code reader and could cancel TC's also.

My 1st suggestion ALWAYS is cancel the code and see HOW quick it comes back (if it does) and IF it is the same code. DTC's are a ROAD SIGN saying "such and such' is about 20 mi. "that" way. They DO NOT have a human brain, nor are they clairvoyant. They are an AID, NOT a laser pointing to EXACTLY what the problem is, at least a lot of the time.

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  • 3 weeks later...

i agree w/ the above post. But for the time being, have autozone clear the code, see if it comes back. If it does then you have two options. 1 being the post cat oxygen sensor (easy fix) or being the cat itself for that bank. U would need to be able to look at live data to be able to tell which one is to blame. If that is not an option then u will have to guess, i would start w/ the cheeper of the two being replacing the o2 sensor then clearing the mil. gl w/ fix

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