1997 Chevrolet Z71 5.7L Engine P0118 Code - Fixed After Sensor Replacement

I recently purchased a 1997 Chevrolet Z71 with a 5.7L V8 engine and discovered it has a persistent P0118 diagnostic trouble code. The vehicle also exhibits difficulty starting. I initially suspected the coolant temperature sensor (ECT) due to inconsistent readings, so I replaced it with a new one. I verified the replacement sensor using an ohms vs. temperature chart — the readings were accurate. I also confirmed proper grounding to the vehicle body, which was intact. After replacing the sensor, I cleared the P0118 code and started the engine while connected to an OBD2 scanner. The ECM still displayed -40°F for coolant temperature even after 30 minutes of driving, and the P0118 code returned immediately. I measured voltage at the yellow wire (pin 23) from the ECT sensor with the key on — reading 3.8 volts. I then disconnected the red connector from the ECM and tested continuity between pin 23 (yellow wire) and the sensor plug end, which showed no issues. Before concluding that the Engine Control Module (ECM) is faulty, I'm seeking input from other owners of 1997 Z71 models with similar P0118 issues. Has anyone encountered this behavior? Any known fixes or troubleshooting steps? Thanks for your insights.