CM871 and CM876 Electronic Control Systems, ISX and ISM Engines – FAULT CODE 1934

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Overview

ISX – EGR Valve Circuit SMALL | MEDIUM | LARGE

ISM – EGR Valve Circuit SMALL | MEDIUM | LARGE

Circuit Description

The exhaust gas recirculation (EGR) valve is a smart device and receives commands from the engine electronic control module (ECM) via the J1939 datalink. The EGR valve performs its own internal diagnostics and reports failures back to the primary engine ECM using the J1939 datalink.

The EGR valve is opened by a motor located on top of the EGR valve. A pin is extended from the motor and contacts the dual-poppet valve to open the EGR valve. The EGR valve motor is not used to close the EGR valve. The pin retracts and a spring is used to close the EGR valve.

Component Location

The EGR valve location can vary depending on engine application. 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 EGR valve detects that the power supply voltage to the EGR valve is less than 8-VDC for more than 5 seconds.

Action Taken When the Fault Code is Active

• The ECM illuminates the amber CHECK ENGINE light immediately when the diagnostic runs and fails.
• EGR valve actuation will continue.

Conditions for Clearing the Fault Code

The ECM will turn off the amber CHECK ENGINE light and enable EGR valve operation immediately after the power supply voltage to the EGR valve is above 8-VDC.

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.

• Verify that the ECM unswitched power is coming from the batteries and not the starter or other devices. Check for possible weak batteries.
• If the ECM unswitched battery supply is taken from the starter, check for low voltage during cranking. Low voltage during cranking can cause the ECM power supply to drop below specifications.

Refer to Troubleshooting Fault Code t05-1934