Fuel Lift Pump Electrical Circuit

When the key is first turned ON without the engine running, the control module turns the fuel lift pump relay ON during the glow plug cycle. This builds up the fuel pressure quickly. If the engine does not start after the glow plug cycle, the control module shuts the fuel lift pump OFF and waits for the engine rpm. As soon as the engine is cranked, the control module turns the relay ON and runs the fuel lift pump. As a back up system to the fuel lift pump relay, the fuel lift pump is also turned ON by an oil pressure switch. When the engine oil pressure reaches about 28 kPa (4 psi) through cranking, the oil pressure switch will close in order to complete the circuit to the fuel pump.

For diagnosis of the lift pump electrical circuit, refer to Fuel Pump Circuit Diagnosis. Testing and Inspection