CM871 and CM876 Electronic Control Systems, ISX and ISM Engines – FAULT CODE 1938

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Overview

ISX – VGT Actuator Circuit SMALL | MEDIUM | LARGE

ISM – VGT Actuator Circuit SMALL | MEDIUM | LARGE

Circuit Description

The variable geometry turbocharger (VGT) is electronically activated by the VGT actuator. The VGT actuator is a smart device and receives information via the J1939 datalink from the primary engine ECM. The VGT actuator performs its own diagnostics and reports failures back to the primary engine electronic control module (ECM) using the J1939 datalink.

Component Location

The VGT actuator is located on the turbocharger bearing housing. Refer to Procedure 100-002 (Engine Diagrams) in Section E for a detailed component location view.

Conditions for Running the Diagnostics

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

Conditions for Setting the Fault Codes

The fault code is set when the voltage supplied to the VGT actuator drops below 10-VDC for 10 seconds and the engine speed must be 0 rpm or above 500 rpm.

Action Taken When the Fault Code is Active

• The ECM illuminates the amber CHECK ENGINE light immediately when the diagnostic runs and fails.
• The VGT actuation will continue until battery voltage drops low enough that VGT actuation can not continue.

Conditions for Clearing the Fault Code

The ECM will turn off the amber CHECK ENGINE light immediately after the voltage to the VGT actuator is greater than 10-VDC and the engine speed is 0 or greater than 500 rpm.

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.

This fault code is logged when the voltage to the VGT actuator drops below 10-VDC. The VGT will still continue to respond to commands from the primary engine ECM.

Refer to Troubleshooting Fault Code t05-1938