The third type of fuel pump control circuit utilizes a two-speed pump electrical circuit. Depending upon engine, the circuit opening relay may be driven by the ECU or by the air flow meter Fc contact. Pump current, however, is supplied either through a current limiting resistor or directly to the pump depending on engine load, rpm and status of the STA signal.
When the engine is cranked, or operated at high speed and/or heavy load, the ECU turns off TR1, closing contact A of the Fuel Pump
Control Relay. This allows current to flow directly to the fuel pump, causing it to run at high speed.
Under all other operating conditions, the ECU turns on TR1, which energizes the Fuel Pump Control Relay. This closes relay contact B and forces current to flow through the resistor, causing the pump to run at low speed. The Fuel Pump Speed Control system is designed to reduce electrical demand and pump wear when fuel demand is low while delivering adequate fuel volume when demand is high.
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