Mercedes-Benz W203 CDI stalls at full throttle and the EPC light comes on

The EPC light indicates an engine power limitation. Stalling is usually caused by the fuel pressure in the injector rail being too low. The system shuts the engine off when the pressure is not sufficient. The fault code often shown is P1187.

The most common causes are air in the fuel hoses or old O-rings, a leaking injector that lets too much fuel into the return line, and a faulty pressure regulator. Less often the fault is in the high-pressure pump or the low-pressure side transfer pump. A clogged fuel filter can also cause the same thing.

First check the hoses and O-rings for air leaks and replace the fuel filter if necessary. Then measure the injector return leak and check the pressure regulator and the pump. An injector leak often shows only on a warm engine, so the test is done when the fault occurs.