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Circuit Description (from FSM)

When the key is in turned ON, the PCM energizes
the fuel pump relay which sends voltage to the lift
pump. The lift pump remains ON during the glow
plug cycle. If the engine is not started immediately
after the glow plug cycle, the PCM shuts the fuel lift
pump OFF and waits until the engine starts. As a
backup system to the fuel pump relay, the fuel lift
pump can (IS) also be turned ON by the fuel pump/oil
pressure switch. When the engine oil pressure
reaches 28 kPa (psi), and the fuel pump relay does
not complete the circuit, the fuel pump/oil pressure
switch will close and complete the circuit to run the
fuel lift pump.

I will add that the OPS energizes the LP circuit at all
times when there is oil pressure no matter what the
LP relay is doing.
 
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