CM871 and CM876 Electronic Control Systems, ISX and ISM Engines – FAULT CODE 1966

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Overview

ISX and ISM – Exhaust Gas Temperature Sensors SMALL | MEDIUM | LARGE

Circuit Description

The exhaust gas temperature sensors are used by the electronic control module (ECM) to monitor the engine exhaust temperatures in the aftertreatment system. The exhaust gas 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 cold, 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 hot, 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 exhaust gas temperature sensors are located in the aftertreatment system.

Conditions for Running the Diagnostics

This diagnostic runs continuously when the engine is running and active regeneration of the aftertreatment diesel particulate filter is not occurring.

Conditions for Setting the Fault Codes

The ECM detects that the exhaust gas temperatures in the aftertreatment system are above a calibratible value for a calibratible amount of time.

Action Taken When the Fault Code is Active

• The ECM illuminates the red STOP ENGINE lamp immediately after the diagnostic runs and fails.
• The engine will shut down if the high temperature condition exists for a calibratible amount of time.

Conditions for Clearing the Fault Code

The ECM will turn off the red STOP ENGINE lamp and the fault code will be set to inactive when the temperatures in the aftertreatment system drop below a calibratible temperature value. The fault code will also be set inactive following a key cycle or if the high temperature condition no longer exists.

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 Section 19.

This fault code is logged when the aftertreatment injector is turned off, but the ECM has detected a high temperature condition in the aftertreatment system. This indicates that a secondary fuel source is entering the aftertreatment system and is creating a temperature increase across the diesel oxidation catalyst and/or diesel particulate filter.

An intermittent fault code condition may be caused by the aftertreatment sensor and related wiring being shorted or damaged (melted), due to component interference. If an intermittent fault code condition exists, inspection of the aftertreatment sensors and wiring for any possible damage is required. Use the appropriate securing methods to make sure the sensor and wiring are not interfering or contacting other components.

Possible causes of this fault code include:

• A damaged fuel injector causing unburned fuel to enter the exhaust system
• Aftertreatment diesel particulate filter inlet temperature sensor failed in-range
• Excessive engine oil being introduced into the exhaust system from the engine or turbocharger
• Aftertreatment temperature sensor has shorted and/or the sensor wiring or connector has been damaged.

The aftertreatment system must be inspected after making the appropriate repair outlined in this fault code troubleshooting tree. Progressive damage to the aftertreatment system may have occurred. Remove the exhaust aftertreatment system from the vehicle for potential malfunction and inspect for reuse. Refer to Procedure 014-013 in Section 14 of the Signature™, ISX, and QSX15 Service Manual, Bulletin 3666239.

Refer to Troubleshooting Fault Code t05-1966