2001 Volvo V70 OBD codes

I do not have a listing for PO422. The PO420 series codes deals with the cat.

P0420/ECM-4201: THREE-WAY CATALYTIC CONVERTER EFFICIENCY
Fault Conditions
ECM controls three-way catalytic converter application after start up by changing between rich and lean fuel mixture. When change takes place the signal from rear heated oxygen sensor and the speed of change are checked. ECM-4201 is stored if ECM registers that rear heated oxygen sensor changes too quickly.

Possible Causes
Air leakage in exhaust system
Defective catalytic converter

Diagnostic Procedure (Power Deterioration)
Check for air leakage and check components. Check for air leakage from the exhaust system. Try a new three-way catalytic converter if no fault has been detected in the exhaust system.