P1404 Fault Code in 2001 Buick 3.1L: EGR System Diagnosis and PCM Wiring Issues

Hi there, I'm experiencing a persistent P1404 diagnostic trouble code on my 2001 Buick 3.1L engine. I've already replaced the EGR valve and cleaned both the throttle body and the EGR passage to the throttle body, yet the code continues to set. After researching, I believe this fault may indicate a diagnostic test failure between the learned zero setting and actual EGR position measurement. I'm wondering if the EGR position sensor is integrated into the EGR valve itself—could that be the source of the issue? Additionally, I suspect there might be a faulty wiring connection to the Powertrain Control Module (PCM). Where exactly is the PCM located in this model? One forum suggested that a failing coolant temperature sensor could also trigger P1404. This may explain why I occasionally notice engine 'chugging'—possibly due to the PCM attempting to relearn or reset the EGR zero setting. I recently took my car to a local mechanic, who performed several EGR function tests while driving and reported that all functions appeared normal during scanning. As I'm preparing for an e-test soon, any insights or troubleshooting tips would be greatly appreciated. Thanks in advance! — Smitty