2002 Fiesta 1.4 TDci P0336 Fault: Sensor Replaced, No MIL On, Engine Won't Start

I'm experiencing a persistent P0336 fault on my 2002 Fiesta 1.4 TDci. I've already replaced the crankshaft position sensor and checked all three wiring connections—no issues found. The check engine light (MIL) does not illuminate when the vehicle is running, but the engine will not start at all. When I disconnect the sensor connector from the engine control unit (ECU), the MIL comes on. Despite replacing the ECU, the same P0336 error persists. Any insights or troubleshooting steps for this specific fault in a 2002 Fiesta 1.4 TDci? Help is greatly appreciated.