PO420 Catalyst code on '02 corolla

[digger89]

Just wanted to share some good news about my recent experience with a PO420 "catalyst system" code and advice from Advance Auto Parts.

First of all, the technicians/salespeople at Advance came out and read the code in the parking lot, no complaints or hassles.

Then after he read the code, I asked "now what" ...I didn't want to replace a whole system or catalytic converter, I didn't even know where to start troubleshooting such a generic code.

The advance auto guru suggested a can of fuel-injection cleaner and reset the code.

So far-300 miles and the code has not re-appeared!

'02 corolla, 80k miles. 70 miles a day round trip to work, 35 mpg on back roads!

[2001CorollaS]

Mine used to do same thing, took 3 tanks of gas for it to come back after clearing it. Cleaned throttle body and used seafoam, problem has been gone for last 5-6 tanks.