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Cummins ISB CM550 (1990-94) Fault Code: 278 PID: 73 SPN: 1075 FMI: 11 (Application for Trucks Other Than Ford) Lift Pump Circuit

Circuit Description
The electronic control module (ECM) enables the lift pump by sending a signal directly to the lift pump. The ECM fast-duty cycles the lift pump ON and OFF during cranking, and it enables the pump once the engine has started.

Component Location
The lift pump is mounted to the engine block on the intake side, toward the rear of the engine.

Shop Talk
1) The lift pump is turned ON for approximately 5 seconds when the keyswitch is first turned ON. With the hood raised, it is possible to hear the lift pump running when the keyswitch is turned ON.
2) Loose battery connections can sometimes cause this fault code.

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