| P0420 relates to the catalytic converter functioning below it's designed threshold. The Powertrain Control Module (PCM) uses O2 sensor data to make the determination, so have a qualified technician diagnose the sensors, just in case they are providing faulty readings.
As for the temp gauge fluctuation, that is unrelated to the trouble code, but still needs diagnosed. Some movement is normal.
Good luck, Bobby. I hope this helps. |