CM871 and CM876 Electronic Control Systems, ISX and ISM Engines – FAULT CODE 1666

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Overview

ISX and ISM – Aftertreatment Temperature Sensors SMALL | MEDIUM | LARGE

Circuit Description

The aftertreatment temperature sensors are used by the electronic control module (ECM) to monitor the engine exhaust temperatures in the aftertreatment system. The aftertreatment temperature sensors are thermistors and change resistance based on the temperature being measured. The ECM provides a 5 volt reference voltage to the sensor. The ECM monitors the change in signal voltage and converts this to a temperature value.

When the exhaust temperature is low, the sensor or thermistor resistance is high. The ECM signal voltage only pulls down a small amount through the sensor to ground. Therefore, the ECM senses a high signal voltage or low temperature. When the exhaust gas temperature is high, the sensor resistance is low. The signal voltage pulls down a large amount. Therefore, the ECM senses a low signal voltage, or a high temperature.

Component Location

The aftertreatment diesel oxidation catalyst inlet temperature sensor is located in the aftertreatment system. It is located at the inlet of the aftertreatment catalyst. Refer to the OEM troubleshooting and repair manual.

Conditions for Running the Diagnostics

This diagnostic runs continuously following a calibratible warm-up period. The diagnostic will not run for a calibratible period of time (up to 5 minutes) following a key cycle.

Conditions for Setting the Fault Codes

The ECM detects that the aftertreatment diesel oxidation catalyst inlet temperature signal voltage is greater than 4.97-VDC for more than 2 seconds.

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 aftertreatment diesel oxidation catalyst inlet temperature reading is used.
• Active regeneration of the aftertreatment diesel particulate filter is disabled.

Conditions for Clearing the Fault Code

The ECM will turn off the amber CHECK ENGINE light immediately after the diagnostic runs and passes.

The ECM detects that the aftertreatment diesel oxidation catalyst inlet temperature sensor signal voltage has returned to normal operating conditions for more than 4 seconds.

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.

The aftertreatment diesel oxidation catalyst inlet temperature sensor shares return wires in the OEM harness with other sensors. A shorted return wire 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 t05-1666