CM871 and CM876 Electronic Control Systems, ISX and ISM Engines – FAULT CODE 1866

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Overview

ISX – Differential Pressure Sensor Circuit SMALL | MEDIUM | LARGE

ISM – Differential Pressure Sensor Circuit SMALL | MEDIUM | LARGE

Circuit Description

The exhaust gas recirculation (EGR) differential pressure sensor has two ports that sense exhaust pressure. The sensor outputs a voltage which represents the pressure difference between the two ports located across an orifice in the EGR tube. The electronic control module (ECM) uses this pressure to determine how much exhaust gas is flowing in the EGR connection tube to the intake manifold. This information is used to control the EGR valve for correct emission levels.

The ECM provides a 5 volt supply to the EGR differential pressure sensor on the sensor supply circuit. The ECM also provides a ground on the sensor return circuit. The EGR differential pressure sensor provides a signal to the ECM on the EGR differential pressure sensor signal circuit. This sensor signal voltage changes based on the differential pressure in the EGR crossover tube.

The EGR differential pressure sensor measures the exhaust gas pressure drop across the EGR differential pressure orifice. This pressure drop is used to calculate the amount of EGR flow into the intake manifold.

Component Location

The sensor is located near the air intake. Refer to Procedure 100-002 (Engine Diagrams) in Section F for a detailed component location view.

Conditions for Running the Diagnostics

This diagnostic runs at key-off when the following conditions are met:

• Engine coolant temperature is 67°C [154°F] or higher.
• Intake manifold air temperature is 7°C [44°F] or higher.
• Keyswitch transitions from ON to OFF.

Conditions for Setting the Fault Codes

The fault code is set active when the EGR differential pressure sensor is reading higher or lower than a calibratible value when the keyswitch is turned off.

Action Taken When the Fault Code is Active

• The ECM illuminates the amber CHECK ENGINE light at key on when the diagnostic runs and fails.
• The EGR valve actuation is disabled.

Conditions for Clearing the Fault Code

• The engine coolant temperature is 67°C [154°F] or higher.
• The intake manifold air temperature is 7°C [44°F] or higher.
• The keyswitch transitions from ON to OFF.
• The reading of the EGR differential pressure must be within the calibratible limits.

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 check is only performed at keyswitch OFF, during the ECM powerdown. During this diagnostic check, the ECM monitors the value of the EGR differential pressure sensor. If this value is outside of a specified range, Fault Code 1866 is set active.

Possible causes of this fault code include:

• A damaged EGR differential pressure sensor.
• High resistance in the wiring harness on the signal or return wire.

Refer to Troubleshooting Fault Code t05-1866