CM871 and CM876 Electronic Control Systems, ISX and ISM Engines – FAULT CODE 144

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Overview

ISX – Engine Coolant Temperature Sensor Circuit SMALL | MEDIUM | LARGE

ISM – Engine 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.

The engine coolant temperature value is used by the ECM for the engine protection system, and engine emissions control.

Component Location

The engine coolant temperature sensor is located on the thermostat housing. Use the following procedure for a detailed component location view. Refer to Procedure 100-002 in Section E.

Conditions for Running the Diagnostics

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

Conditions for Setting the Fault Codes

The ECM detects that the coolant temperature signal voltage is greater than 5.13-VDC for more than 1 second.

Action Taken When the Fault Code is Active

• The ECM illuminates the amber CHECK ENGINE light immediately when the diagnostic runs and fails.
• A default value for the coolant temperature reading is used.

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 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. Use the following procedure in the corresponding Troubleshooting and Repair Manual for the engine being serviced. Refer to Procedure 019-032 in Section 19.

Before troubleshooting Fault Code 144, check for multiple faults.

The engine coolant temperature sensor shares return wires in the engine harness with other sensors. An open return can cause multiple fault codes to be active.

Possible causes of this fault code include:

• Open return circuit in the harness, connectors, or sensor.
• Open signal circuit or shorted to a voltage source.

Refer to Troubleshooting Fault Code t05-144