2004 Monte Carlo 3.4L P0452 and P0171: Fuel Tank Pressure and Lean Running Issues After Fuel Pump Replacement
New member here — hoping I'm in the right section. I own a 2004 Monte Carlo with a 3.4L engine, currently at 76,000 miles. One week ago, I had my fuel pump replaced. Last Thursday, the 'Check Engine' light came on — this has never happened before in the vehicle's history. On Friday evening, after driving for about 10–15 minutes, the car stalled while braking from 40 mph. I pulled over, restarted immediately, and no issues occurred during that restart. Over the weekend, I drove approximately 30 miles without any problems. However, this morning, the vehicle stalling occurred twice on my commute — each time during a brake event with the foot off the accelerator. The same behavior happened when I drove to lunch and returned home. On the way home, I stopped to have the codes scanned, which revealed P045-2 (Fuel Tank Pressure Condition) and P0171 (Fuel Trim Bank One — Running Lean). I've reviewed posts about these individual trouble codes, but I'm seeking insight into how they might be related. Any advice or explanations on what could cause both codes simultaneously would be greatly appreciated.
It's highly likely the issue is connected to the recent fuel pump work. The P0452 and P0171 codes are often linked — especially after a fuel system repair. Possible causes include a vacuum or purge hose not properly installed during the pump replacement, a faulty fuel pressure sensor located at the top of the fuel pump assembly, or an oversite in the installation process. I strongly recommend returning to the shop that performed the work and clearly stating that the codes point to a potential fuel delivery issue related to the pump or sensor.