Toyota Yaris 1.5 T-Sport Age: 4 years Mileage: 26k
We have a problem with the MIL coming on every few weeks on the above car. I recently bought a PC interface and read the fault code. The code is P0420: catalytic convertor performance below threshold.
After some studying on the web, I went out with SWMBO to study graphs of the O2 sensor behaviour on the laptop whilst on the road (her driving, of course :-)). Sensor 1 behaves normally, switching ON/OFF constantly, except on overrun, where it remains OFF. Unfortunately, it seems that sensor 2 (downstream of CAT) is mimicking this behaviour and switches almost as regular as the upstream sensor. I believe that it should maintain a low value (around 0.2v) most of the time, correct?
Based on the above it would seem that we have a very premature catalytic converter failure :-( I am considering approaching Toyata with a view to obtaining a free replacement, or at least a substantial contribution to the cost. Americans get an 8 year warranty on them! Before I do this, I would like to ask if there's anything I may have missed? Do the sensors sometimes go out of tolerance and become oversensitive? Is there something else I could have overlooked? I have checked values of CTS, MAF etc. Long term fuel trim is only a very small adjustment at -3%. Everything else seems normal. Any ideas?