Electronically controlled fuel injector is a solenoid valve which supplies exactly calculated amount of fuel to engine for optimum conbustion under various engine load and speed. To meet air-fuel ratio required in system, ECM regulates fuel injection quantity as controlling injector solenoid operating duration referring air flow to cylinders and output signals from HO2S. For this precise control, quick response of solenoid is required and for perfect combustion, injection characteristic is important.

If there is Open in injector #4 circuit, ECM sets DTC P0204.

When the ECM energizes the injector by grounding the control circuit, the circuit voltage should below (theoretically 0V) and the fuel is iniected. When the ECM de-energizes the injector by opening control circuit, the fuel injector is closed and circuit voltage should be peak for a moment.