Q&A

 Technician

Ok lets start with the easy one p0420 Cat System Efficiency Below Threshold Bank 1 you most likely need a catalytic converter replaced. Now for p0322 (I am assuming you are mechanically inclined) Check all fuses. Test the connector for the G28 engine speed sensor at the firewall connection for corrosion or loose contact. At the connector for the ECM, check resistance between the two pins for the engine speed sensor. Pin number 82 has a Gray wire, and 90 has a Blue wire. The resistance reading through the sensor should be between 730 and 1000 ohms. If resistance is good, crank the engine and reading AC voltage between pins 82 and 90. The voltage reading should be greater than 1 V AC while cranking. If the Engine Speed Sensor fails either test above, it should be replaced. If you need our services we can be reached at support@aerboise.com or 208-424-6717 hope this helps.

 Master

Very good practical answer "aer auto repair". I had an intermittent problem on my BMW, I didn't want to carry around my oscilloscope and wrote what all the ac voltage readings should be for a "healthy sensor".

 Journeyman

this obd2 trouble code table can help you understand the meaning of code.
http://www.chinasinoy.com/service/how-to-understand-troub...
for this code, you can try the following solution:
Check for exhaust leaks at the manifold, pipes, catalytic converter. Repair as required.
Use a scope to diagnose the oxygen sensor operation (Tip: The oxygen sensor in front of the catalytic converter normally has a fluctuating waveform. The waveform of the sensor behind the converter should be more steady).
Inspect the downstream heated oxygen sensor (HO2), replace if necessary
Replace the catalytic converter