Cummins ISB4.5 CM2150 Fault Code: 321 PID: SID 4 SPN: 654 FMI: 6 Injector Solenoid Driver Cylinder 4 Circuit – Current Above Normal or Grounded Circuit.

Circuit Description
The injector solenoid valves are actuated by the electronic control module (ECM) to control fuel metering and timing. Each injector solenoid is connected to the ECM by a supply and a return wire. An electrical pulse is sent to the injector from the ECM on the supply wire and returns to the ECM on the return wire after actuating the solenoid. Each solenoid valve is normally open, and it is only closed by an electrical pulse from the ECM during fuel injection and metering.

Component Location
The ISM has an internal actuator harness that connects to the external engine harness with a 15-pin connector at the front side of the rocker lever housing. The internal actuator harness is located on the inside of the rocker lever housing on the right side. It has six connectors spaced along its length; one for each injector solenoid. These connectors attach to the pigtail connector on each injector.

Conditions for Running the Diagnostics
This diagnostic runs continuously when the engine speed is greater than 0 rpm.

Conditions for Setting the Fault Codes
The ECM detects that the injector circuit is shorted to a voltage source, shorted to a battery source, or low injector solenoid resistance.

Action Taken When the Fault Code is Active
-The ECM illuminates the amber CHECK ENGINE light immediately when the diagnostic runs and fails.
-The injector will be disabled.

Conditions for Clearing the Fault Code
The ECM will turn off the amber CHECK ENGINE light immediately after the diagnostic runs and passes.

Possible Causes
-Open circuit in the engine harness, connectors, or actuator.
-Short circuit to voltage source in the engine harness.
-Short circuit to ground in the engine harness or injector.
-Low or high resistance in the injector.