The engine warning light came on so I plugged in a diagnostic computer and it said there was a P0420 Catalyst System Efficiency Below Threshold. Anyone have any ideas what the cause is and how to resolve it? Thanks in advance.
I got this when I decatted my car and hadn't turned off the secondary O2 sensors as being an emissions warning. For you it could be that the cats have collapsed/expired or the secondary O2 sensor is faulty/unplugged.
