Every couple of months the check engine light on my 2000 Nissan Maxima SE (125K miles) comes on. The OBD-II code is P0420 “Catalyst system efficiency below threshold (bank 1)”
I clear the code, and the SES light stays off for a few more months.
1. Does this really mean I need to change the cat?
2. Could it be O2 sensor(s)? (they’re the original ones)
3. Can I just ignore it?
It could be the oxygen sensor. Only by checking the sensor sigals can you tell.
I don’t recommend ignoring it. By doing so you basically render your CEL less useful. Some other problem might arise and you’ll think it’s just the same ol’ thing…and the new problem may dod damage.