CM871 and CM876 Electronic Control Systems, ISX and ISM Engines – FAULT CODE 1973

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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 gas 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 high temperature.

Component Location

The aftertreatment diesel particulate filter outlet temperature sensor is located in the aftertreatment system. It is located at the outlet of the aftertreatment diesel particulate filter. Refer to the OEM service manual.

Conditions for Running the Diagnostics

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

Conditions for Setting the Fault Codes

The ECM detects that the aftertreatment diesel particulate filter outlet temperature reading is greater than 800°C [1472°F] for 15 seconds.

Action Taken When the Fault Code is Active

• The ECM illuminates the red STOP ENGINE light immediately when the diagnostic runs and fails.
• Active aftertreatment diesel particulate filter regeneration will be disabled.
• The exhaust gas recirculation (EGR) valve operation will be disabled.
• Possible engine shutdown if the engine protection shutdown feature is enabled.

Conditions for Clearing the Fault Code

The ECM will turn off the red STOP ENGINE light and the fault code will be set to inactive when the keyswitch is cycled.

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.

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
• A damaged aftertreatment fuel injector
• Aftertreatment diesel particulate filter outlet 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. Use the procedure found in the ISM, ISMe and QSM11 Service Manual, Bulletin 3666322, or the Signature™, ISX, and QSX15 Service Manual, Bulletin 3666239. Refer to Procedure 014-013 in Section 14.

Refer to Troubleshooting Fault Code 1973.