How do i test the voltage and the ground on the PCM on my 2009 Nissan Cube?

First check the automatic speed control device (ASCD) brake switch for proper operation and adjustment. Does the cruise control feature work? There is a Technical Service Bulletin regarding this, so address that before testing otherwise. Besides that, there is a test procedure, but usually the ECM is a concern internally for the P0605 code. I do not see anything in the test procedure indicating to check for voltage and ground. P0420 is related to catalytic converter internal inefficiency. A likely secondary concern here.