Cummins ISB CM550 (1990-94) Fault Code: 373 PID: SID 233 SPN: 1077 FMI: 3 Fuel Pump Fuel Shut Off Error

Circuit Description
This circuit provides a secondary fuel shutoff signal from the engine control module (ECM) to the fuel pump.

Component Location
The fuel pump is located on the back side of the gear housing.

Shop Talk
The fuel pump controller disables fuel injection if a greater-than-6-VDC signal is registered at pin 5 (pump connector end) for 1 second. This signal line is triggered if an engine protection limit is exceeded or if a pump controller defect is set.
Normal engine operation is as follows:
1) 0-VDC at pin 5 at keyswitch ON
2) 12-VDC at pin 5 at keyswitch OFF, until ECM powers down.
Check for a short circuit in the wiring harness, bad connectors, or high voltage at engine harness pin 5on the pump end at keyswitch ON.