Circuit Opening Relay

Circuit opening relay controls fuel pump circuit. ECU receives input signal at STA terminal (ST terminal on LS400) when engine is cranking. This same starter signal is also applied to terminal STA (or ST) of circuit opening relay. Starter signal energizes circuit opening relay during cranking, which in turn activates fuel pump (through fuel pump relay on LS400). 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. Circuit opening relay is located next to ECU.