CM871 and CM876 Electronic Control Systems, ISX and ISM Engines – FAULT CODE 255

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Overview

ISX – Engine Fuel Shutoff Valve Driver Circuit SMALL | MEDIUM | LARGE

ISM – Engine Fuel Shutoff Valve Driver Circuit SMALL | MEDIUM | LARGE

Circuit Description

The fuel shutoff valve is a device used by the electronic control module (ECM) to control the engine fuel supply. When the ECM energizes the engine fuel shutoff valve driver circuit, the engine fuel shutoff valve is opened. Zero voltage to the engine fuel shutoff valve will close the engine fuel shutoff valve.

The engine fuel shutoff valve driver circuit utilizes a pulse width modulated (PWM) signal. A PWM signal is a pulsed voltage signal between 0-VDC and system voltage.

Component Location

The fuel shutoff valve is located near the fuel pump. Refer to Procedure 100-002 (Engine Diagrams) in Section E for a detailed component location view.

Conditions for Running the Diagnostics

This diagnostic runs continuously when the keyswitch is in the ON position.

Conditions for Setting the Fault Codes

The engine fuel shutoff valve circuit PWM signal is detected to be at system voltage when the PWM voltage is turned off.

Action Taken When the Fault Code is Active

• The ECM illuminates the amber CHECK ENGINE light immediately when the diagnostic runs and fails.
• The engine will be shutdown and will not restart.

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.

If there is an external shutdown system on the vehicle, make sure it is not miswired and feeding voltage into the fuel shutoff supply circuit.

Possible causes of this fault include:

• Open circuit in the engine harness, connectors, or shutoff valve.
• Fuel shutoff valve signal wire shorted to a voltage source in the harness.

Refer to Troubleshooting Fault Code t05-255