Circuit Opening Relay Operation

Circuit opening relay controls fuel pump circuit. ECU receives input signal at STA terminal when engine is cranking. This same starter signal is also applied to terminal STA of circuit opening relay. Starter signal energizes circuit opening relay during cranking, which in turn activates fuel pump.

On ES250, when airflow meter senses airflow to engine, fuel pump switch in airflow meter provides an alternate relay ground.

On LS400, circuit opening relay is grounded by ECU through FC terminal. The relay is located next to the ECU.