CM871 and CM876 Electronic Control Systems, ISX and ISM Engines – FAULT CODE 2789

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Overview

ISX Coolant Temperature Sensor Circuit SMALL | MEDIUM | LARGE

ISM Coolant Temperature Sensor Circuit SMALL | MEDIUM | LARGE

Circuit Description

The coolant temperature sensor is a variable resistor sensor and is used to measure the temperature of the coolant of the engine. The electronic control module (ECM) supplies 5 volts to the coolant temperature signal circuit. The ECM monitors the change in voltage caused by changes in the resistance of the sensor to determine the coolant temperature.

Component Location

The engine coolant temperature sensor is located on the exhaust side of the engine near the thermostat housing. 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 engine is running.

Conditions for Setting the Fault Codes

The ECM detects that the coolant temperature is below a calibratible limit set in the ECM.

Action Taken When the Fault Code is Active

The ECM will set the fault code active immediately after the diagnostic is set.

Conditions for Clearing the Fault Code

The fault code will be set inactive when the coolant temperature is detected to be within the normal operating temperature limits.

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 this fault indicates that coolant temperature is below a calibratible limit set in the ECM.

• For ISM engines, refer to Engine Coolant Temperature Below Normal troubleshooting symptom tree tree in the ISM, ISMe and QSM11 Service Manual, Bulletin 3666322.
• For ISX engines, refer to Engine Coolant Temperature Below Normal troubleshooting symptom tree tree in he Signature, ISX and QSX15 Service Manual, Bulletin 3666239.

Refer to Troubleshooting Fault Code t05-2789