P0420 Code on Toyota Corolla – Is It Safe to Drive and How Do I Fix It?
Quote from CheckEngineChamp on June 9, 2025, 9:07 amHey everyone,
I have a 2013 Toyota Corolla and recently got a P0420 code after the check engine light came on. I used my Innova OBD2 scanner to read the code, and it says “Catalyst System Efficiency Below Threshold.”
The car still runs fine, but I want to know:
Is it safe to keep driving with the P0420 code?
What are the common causes and permanent fixes for this code on a Corolla?
Any advice from those who’ve dealt with this before would be super helpful.
Thanks!
Hey everyone,
I have a 2013 Toyota Corolla and recently got a P0420 code after the check engine light came on. I used my Innova OBD2 scanner to read the code, and it says “Catalyst System Efficiency Below Threshold.”
The car still runs fine, but I want to know:
-
Is it safe to keep driving with the P0420 code?
-
What are the common causes and permanent fixes for this code on a Corolla?
Any advice from those who’ve dealt with this before would be super helpful.
Thanks!
Quote from AutoFixerMike on June 9, 2025, 9:11 amYou can usually drive short-term with a P0420, but it means your catalytic converter isn’t performing efficiently. I had the same issue on my 2010 Corolla.
In my case, it was a bad downstream oxygen sensor — much cheaper to replace than the cat. I used an Autel scanner to confirm sensor voltage.Fix that first before replacing the catalytic converter!
You can usually drive short-term with a P0420, but it means your catalytic converter isn’t performing efficiently. I had the same issue on my 2010 Corolla.
In my case, it was a bad downstream oxygen sensor — much cheaper to replace than the cat. I used an Autel scanner to confirm sensor voltage.
Fix that first before replacing the catalytic converter!
Quote from ScanToolGuru on June 9, 2025, 9:17 amCommon causes:
Bad or lazy O2 sensors
Small exhaust leaks
Aftermarket catalytic converter not functioning well
Try clearing the code and see if it comes back. If it does, scan the O2 sensor readings while driving (live data helps a lot).
Common causes:
-
Bad or lazy O2 sensors
-
Small exhaust leaks
-
Aftermarket catalytic converter not functioning well
Try clearing the code and see if it comes back. If it does, scan the O2 sensor readings while driving (live data helps a lot).
Quote from LadyGreaseHands on June 9, 2025, 9:27 amI’ve had this on my Corolla twice. First time it was a faulty rear O2 sensor, second time it was an exhaust leak near the manifold. Both gave me the same P0420 code.
Lesson learned: always check for leaks before spending big on parts!
I’ve had this on my Corolla twice. First time it was a faulty rear O2 sensor, second time it was an exhaust leak near the manifold. Both gave me the same P0420 code.
Lesson learned: always check for leaks before spending big on parts!
Quote from DIYDan on June 9, 2025, 9:36 amTemporary fix: use cat cleaner fuel additives (like Cataclean). Sometimes they help, especially if your converter is just clogged.
But don’t rely on it long term. Replacing the downstream O2 sensor worked for me. Parts cost me around $60.
Temporary fix: use cat cleaner fuel additives (like Cataclean). Sometimes they help, especially if your converter is just clogged.
But don’t rely on it long term. Replacing the downstream O2 sensor worked for me. Parts cost me around $60.
Quote from Kevin Nicholas on June 10, 2025, 7:44 amJust make sure you don’t ignore it too long. If your cat fails completely, it could damage your engine or cause fuel economy issues.
Get a scan tool that shows live O2 sensor voltages — it’ll help you pinpoint the problem. Also, reset the code after any changes to see if it returns.
Just make sure you don’t ignore it too long. If your cat fails completely, it could damage your engine or cause fuel economy issues.
Get a scan tool that shows live O2 sensor voltages — it’ll help you pinpoint the problem. Also, reset the code after any changes to see if it returns.