CM871 and CM876 Electronic Control Systems, ISX and ISM Engines – FAULT CODE 321

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Overview

ISM – Injector Solenoid Driver Cylinder 4 Circuit SMALL | MEDIUM | LARGE

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 exhaust 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.

Shop Talk

Verify the electronic control module (ECM) calibration is correct. Check the calibration revision history found on QuickServe® Online for applicable fixes to the calibration stored in the ECM. If necessary, recalibrate the ECM. Refer to Procedure 019-032 (ECM Calibration Code) in Section 19 in the corresponding Troubleshooting and Repair Manual for the engine being serviced.

Possible causes for this fault code include:

• Open circuit in the engine harness, connectors, or actuator.
• Short circuit to voltage source in the engine harness.
• Short circuit between the injector (+) and injector (-) in the engine harness.
• Low or high resistance in the injector.

Refer to Troubleshooting Fault Code t05-321