Fuel Pump Electronic Control Unit & Fuel Pump Switch (Land Cruiser)
Fuel pump operating speed is controlled by engine operating conditions 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 Electronic Control Unit (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 engine is under heavy load at high speeds, ECM delivers input signal of approximately 3.8 volts to fuel pump ECU. Fuel pump ECU then delivers approximately battery voltage to fuel pump and fuel pump operates at high speed. When engine is under heavy load at low speeds, ECM delivers an input signal of approximately 2.5 volts to fuel pump ECU. Fuel pump ECU then delivers approximately 10 volts to fuel pump and fuel pump operates at medium speed. When engine is idling or under light loads, ECM delivers an input signal of approximately 1.3 volts to fuel pump ECU. Fuel pump ECU then delivers approximately 8.5 volts to fuel pump and 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 TESTING PROCEDURE under SELF-DIAGNOSTIC SYSTEM in appropriate SELF-DIAGNOSTICS article for retrieving of DTCs. Fuel pump ECU is located behind inner panel, just behind driver's rear wheelwell. See Fig 1.
Fuel pump switch is in the circuit between FPC terminal on ECM 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.