For a long while my car has thrown the P0620 code which means the voltage is below a certain number. We tested the voltage on the car at the battery and it shows 13.8-14.2 and the alternator tested fine. My question is, the voltage at the PCM is reading wrong and showing under 12 volts which is causing this code. What is the procedure for testing it at the pcm and why is the computer not seeing the proper voltage? PCM and engine is a 2000 GTP setup.