CM871 and CM876 Electronic Control Systems, ISX and ISM Engines – FAULT CODE 1667

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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 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 (low temperature). When the exhaust gas temperature is high, the thermistor resistance is low. The signal voltage pulls down a large amount. Therefore, the ECM senses a low signal voltage,
(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 diesel oxidation catalyst. Refer to the OEM service manual.

Conditions for Running the Diagnostics

This diagnostic runs continuously when the engine is running and fuel injection into the aftertreatment system is not
occurring.

Conditions for Setting the Fault Codes

The ECM detects that the aftertreatment diesel oxidation catalyst inlet temperature sensor reading is not
changing with engine operating conditions.

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 engine must be running at 1200 RPM or above for 15 minutes and the aftertreatment diesel oxidation catalyst inlet temperature must be above 150°C
[302°F] before the fault code will clear.

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, calibrate the ECM. Refer to Procedure 019-032 in Section19.

The aftertreatment sensors share a common ground wire with the coolant level sensor. Fault codes or problems related to the coolant level sensor and its ground circuit could potentially cause this fault.

Possible causes of this fault code include:

• Coolant level sensor and/or coolant level sensor ground circuit fault codes or related problems
• Stuck in-range aftertreatment diesel oxidation catalyst inlet temperature sensor
• High resistance in the aftertreatment diesel oxidation catalyst inlet temperature sensor signal or return lines
• A face plugged or damaged aftertreatment diesel oxidation catalyst.

Refer to Troubleshooting Fault Code t05-1667