PO420.....so now what? - Toyota Yaris Forums

eTiMaGo · 03-29-2009, 11:17 AM

Here's as detailed as you can get:

P0420 Catalyst System Efficiency Below Threshold (Bank 1)

Causes:
- Front exhaust pipe (with Three-Way Catalytic Converter)
- Gas leakage from exhaust system
- A/F sensor (sensor 1)
- HO2 sensor (sensor 2)

If it was a timing error or plug not tight, you'd have a different code, that's the whole reason for being of these diagnostic codes, to help you pinpoint the problem, not maybe something else

Thanks for posting the stored freeze frame value, quite interesting! Only thing that I think is out of order: Bank 1 - Sensor 1 O2S Voltage 3.44 V

Looking at the repair manuals the normal range for this sensor should be usually less than 1V? So yes, in this case, it seems to narrow the problem down to the O2 sensor being defective. But don't take my word for it, I am not a qualified mechanic, just a geek who likes to look up and understand technical information

03-29-2009, 11:17 AM	#11
eTiMaGo vroom vroom View User's Garage Drives: lil red 5-door Join Date: Sep 2006 Location: Bangkok, Thailand Posts: 7,744	Here's as detailed as you can get: P0420 Catalyst System Efficiency Below Threshold (Bank 1) Causes: - Front exhaust pipe (with Three-Way Catalytic Converter) - Gas leakage from exhaust system - A/F sensor (sensor 1) - HO2 sensor (sensor 2) If it was a timing error or plug not tight, you'd have a different code, that's the whole reason for being of these diagnostic codes, to help you pinpoint the problem, not maybe something else Thanks for posting the stored freeze frame value, quite interesting! Only thing that I think is out of order: Bank 1 - Sensor 1 O2S Voltage 3.44 V Looking at the repair manuals the normal range for this sensor should be usually less than 1V? So yes, in this case, it seems to narrow the problem down to the O2 sensor being defective. But don't take my word for it, I am not a qualified mechanic, just a geek who likes to look up and understand technical information __________________ The price of freedom of religion, or of speech, or of the press, is that we must put up with a good deal of rubbish. - Robert Jackson Bye bye 1NZ...