ASP20

May someone please tell me what you think is wrong with my car?
I have a 2002 RX300 with ~110k miles and as I was driving this last weekend the VSC and CEL lights came on my dash. I had the car diagnosed at Autozone and they told me the code is P0420:
Definition: Catalyst efficiency below threshold - bank 1 Probably cause:
1. - Failed catalytic converter
2. - Ignition system malfunction
3. - Fuel syste malfunction
Thank you.

hypervish

Welcome to Club Lexus!

Often times that code is thrown due to a bad 02 sensor at Bank 1, Sensor 2.

DIY found here: https://www.clublexus.com/forums/rx-...sor-2-diy.html

ASP20

Hypervish, thank you for the welcome. Thank you for the quick response and the link to lexmex DIY. Could it also possibly be one of the A/F Sensors OR the catalytic converter? If it could be the catalytic converter, what may I expect to pay just for the part(catalytic converter) and then what may I expect to pay for installation? If I decide to replace the O2 senser, can I replace it with the Denso 234-4215 Oxygen Sensor from Amazon? Thank you.

hypervish

Unlikely for it to be any of the A/F sensors. It is definitely possible for it to be a catalytic converter issue, however with the low miles that it has (yes,110k miles is low to me lol), this is unlikely.

OEM Catalytic converter will be outrageous, willing to bet well north of $1000. It's easiest if you bought the BOSAL rear converter with resonator assembly for around $300. Labor to install should be around 1 hour.

Replacing this sensor is the cheapest solution, and by far the easiest. Not suggesting you throw parts at it, you can test the sensor before replacing. There is a DIY for that.

ASP20

Dear hypervish, Thank you so much for all the information you provided. I was able to replace the 02 Sensor this past weekend thanks to the information you provided and the lexmex DIY video. I was able to disconnect the electrical connection of the old sensor and connect the new sensor without having to cut a bigger hole in the carpet under the driver's seat. I was able to remove one of the mounting bolts that holds the sensor to the muffler but rounded off the head of the other bolt and had to have a local garage remove it(~$40). I applied anti-seize to both mounting bolts when I installed the new sensor hoping that will make it easier to remove should I have to replace the sensor again. Thanks again!

ASP20

Dear hypervish, My VSC CEL warning lights came on again this past weekend. I took the car to both Auto Zone AND Advance Auto to have the problem diagnosted and both said the code is P0420 again. I got my brand new sensoe off Amazon, do you think I got a bad sensor, or is there something else that may be causing the problem. Also, my sensor mount has a what looks to be a heat shield that protects one side of the sensor. Should the shield be between the sensor and the Cat or on the other side of the sensor? I mounted it with the shield between the sensor and the Cat. Thank you.

hypervish

Which sensor did you buy? Denso 234-4215, right?

It's unlikely for the new sensor to be bad. Did you test the old sensor before replacing?

ASP20

Yes I bought the Denso 234-4215. I did not test the old sensor. How do I test the sensor?

hypervish

Similar process to what's found here:https://www.clublexus.com/forums/rx-...esistance.html

However resistance numbers may be different for an 02 sensor. I'm not familiar with what numbers you should be looking for, hopefully someone can chime in.