I have a 1996 SC400. The check engine light and the trac off light came on. I had the code checked and it read P0420.
Catalyst System Efficiency Below Threshhold Bank 1
I had done a few searches and I believe this is the oxygen (o2) sensor but I am not sure. All I could find has really for the pre OBDII models. Has anyone had this problem? Was it fixed by replacing the O2 sensor, or am I going to have to get new cats?
Also, which bank is 1, driver sdie or passenger side?

Thanks,
Adam

 

I now have the same exact problem, and I'm wondering if This Bank one is on the Drivers, or Passenger side? Is it a bad sensor or bad Cat?

 

Check the down stream 02 sensor voltage. If it is switching like the upstream 02 then you will need a new cat.

 

I believe bank 1 is Drivers side. On my stang that threw the same code though it said bank 0 was 0420 and it was passenger side.