Toyota Tundra 2005 Service - Repair - Maintenance page 441

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CIRCUIT DESCRIPTION

In the diagram below, when the engine is cranked, current flows from terminal STAR of the ECM to the starter

relay coil and also current flows to terminal STA of the ECM (STA signal).

When the STA signal and NE signal are input to the ECM, the Tr1 is turned ON, current flows to the coil of

the circuit opening relay, the relay switches on, power is supplied to the fuel pump, and the fuel pump oper-

While the NE signal is generated (engine running), the ECM keeps the Tr1 ON (circuit opening relay ON)

and the fuel pump also keeps operating.

The fuel pump speed is controlled at two levels (high speed or low speed) by the condition of the engine

(starting, light load, heavy load). When the engine starts (STA ON), the Tr2 in the ECM is OFF, so the fuel

pump relay closes and battery positive voltage is applied directly to the fuel pump. The fuel pump operates

at high speed.

After the engine starts while idling or light loads, since the Tr2 goes ON, power is supplied to the fuel pump

via the fuel pump resistor. The fuel pump operates at low speed.

Ignition Switch

Fuel Pump Primary Circuit

Circuit Opening

Starter Relay

ENGINE (1GR−FE)

Fuel Pump Resistor

Fuel Pump Relay

Crankshaft Position

Sensor (NE Signal)