2005 Renault Megane 1.9dci P0409 and P0670: Loss of Power Above 2000 RPM, EGR Replacement History

Hello everyone, My 2005 Renault Megane 1.9dci has recently developed a recurring issue involving the 'Service' light and an 'Injection Fault' message. The problem first appeared during a routine service check, when the dashboard displayed 'Check Injection' and OBDII returned code P0670 — which I believe refers to the GPCM (Governor Pressure Control Module). At that time, there were no noticeable performance issues, and fuel consumption remained normal. I initially dismissed it due to anecdotal reports from other owners experiencing similar symptoms without any adverse effects. However, last week after a 30-mile drive, the 'STOP' light illuminated along with an 'Injection Fault' message. This was accompanied by a significant loss of power above 2000 RPM — the engine would spool up to around 1000 RPM but then drop off at higher speeds. The turbo did not maintain boost pressure beyond that point. I scanned the vehicle and found both P0409 (EGR Circuit A) and P0670. Since then, it has run normally with no further symptoms until this morning, when the same issue reoccurred. I turned off the ignition, restarted the car, and the warning message disappeared — power returned to full levels. I recently replaced both the EGR valve and MAF sensor due to a similar incident, so I don’t believe that component is at fault. The symptoms are consistent with an EGR stuck open (causing reduced boost), but previously there was no 'STOP' light or P0970 code — which makes this less likely. One forum suggestion pointed to the optical sensor in the injection pump as a potential cause. Is this plausible? Could a faulty injection pump sensor trigger both P0409 and P0670? Any insights, troubleshooting steps, or known fixes for this issue on the 2005 Renault Megane 1.9dci would be greatly appreciated. Best regards, Tom