Cummins ISB CM550 (1990-94) Fault Code: 377 PID: SID 233 SPN: 107 FMI: 7 Fuel Pump Power Relay Stuck-On

Circuit Description
This circuit is internal to the ECM. If the keyswitch is turned off and the ECM still detects
messages being sent from the fuel pump, the ECM will log this fault.

Component Location
This circuit logic is internal to the ECM.

Shop Talk
1) Some older ISB engines use a different original equipment manufacturer (OEM) interface
connector than illustrated.
2) Fault Code 377 can be caused by a stuck fuel pump relay. If voltage is detected at pin 7
of the fuel pump connector, with the keyswitch in the OFF position, check for a faulty fuel
pump relay.