P0420 - Corolla 01

01-24-2017, 01:13 PM
The Diagnosis says to get a catalytic converter but I've been doing some reading in hears and it can be a number of things Oxygen Sensor - Mass Airflow,

1. Question is there a test besides the regular Diagnosis test from Auto Zone or Adv Auto or NAPA. Is there a test to check out the exhaust system to see if it is other things beside the catalytic converter.

2. My Check engine light just came on (and Now its off but I still think the problem persists) about the beginning of January so not even a month ago. I know this is important but how long can I get by with it and not cause any serious damage to my car.

01-25-2017, 01:38 PM
if the car has over 100k miles it would not be a bad idea to change the O2 sensors anyway and you can check what voltage the sensors are putting out with a decent code reader and right procedure. can also ask a exhaust shop to see if cat is working right but they only make money if they replace it so hard to say if they are a good shop or not

01-26-2017, 11:12 AM
I do not know about your 01 but Toyota's P0420 code means cat efficiency is below 95%. Before spending money on a new O2 I would try to install anti fowler (about $5 on Ebay), clear code and see if it comes back.

Good luck,

Brian R.
01-27-2017, 08:32 AM
If the code is intermittent, disconnect the HO2 sensor (the sensor after the cat convertor) connector, clean it and restore the connection. If the code persists, replace the HO2 sensor after the convertor. Get the part number for the sensor from a Toyota parts department by giving them your VIN. Then go to the DENSO website and cross-reference the Toyota part number with the DENSO part number. Get the sensor from Amazon.com with the DENSO part number (Downstream oxygen sensor).

Shadab Lodhi
12-04-2017, 05:17 PM
Clean the CAT with a soft brush and the problem will be solved. If the problem persists check the muffler for any leakage.

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