Fuel Pump Electronic Control Unit (ECU) & Fuel Pump Switch (LX470)
Fuel pump operating speed is controlled by operating condition of the engine such as: starting, idling, light load or heavy load. Engine Control Module (ECM) delivers an input signal from FPC terminal on ECM to FPC terminal on fuel pump ECU in accordance with engine operating condition. Fuel pump ECU uses this input signal to determine how much voltage should be delivered to fuel pump for varying fuel pump operating speed. When engine starts or is under heavy load with engine at high speed, ECM delivers about 3.8-volt input signal to fuel pump ECU. Fuel pump ECU then provides battery voltage to fuel pump so fuel pump operates at high speed. When engine is under heavy load with engine at low speed, ECM delivers about 2.5-volt input signal to fuel pump ECU. Fuel pump ECU then provides about 10 volts to fuel pump so fuel pump operates at medium speed. When engine is idling or under light load, ECM delivers about 1.3-volt input signal to fuel pump ECU. Fuel pump ECU then provides about 8.5 volts to the fuel pump so fuel pump operates at low speed. If a problem exists in fuel pump ECU or control circuit, Diagnostic Trouble Code (DTC) P1200 may be stored in ECM. See SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - INTRODUCTION article for retrieving of DTCs. Fuel pump ECU is located behind inner panel, just behind driver's side rear wheelwell. See Fig 1.
Fuel pump switch is in the circuit between FPC terminal on ECU and FPC terminal on fuel pump ECU. Fuel pump switch may also be referred to as fuel pump inertia switch or fuel pump control switch. If vehicle is involved in a collision, fuel pump switch will shut off the fuel pump by opening this circuit, and not allowing any input signal to be delivered from ECM to fuel pump ECU. Fuel pump switch is located on driver's side of instrument panel. See Fig 2. Fuel pump switch contains a reset switch which has an OFF and ON position. See Fig 2. Continuity will exist between electrical terminals on fuel pump switch with reset switch in the ON position, and no continuity in the OFF position. Reset switch must be in ON position for fuel pump operation.