CM871 and CM876 Electronic Control Systems, ISX and ISM Engines – FAULT CODE 1899

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Overview

ISX – Differential Pressure Sensor SMALL | MEDIUM | LARGE

ISM – Differential Pressure Sensor 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. The 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 electronic control module (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

Refer to Procedure 100-002 in Section E.

Conditions for Running the Diagnostics

This diagnostic runs continuously when the following conditions are met:

• EGR valve position is greater than 5 percent open.
• Engine speed is greater than 1200 rpm.
• Engine torque output is greater than a calibratible value.

Conditions for Setting the Fault Codes

EGR differential pressure is less than a calibratible value.

Action Taken When the Fault Code is Active

• The ECM illuminates the amber CHECK ENGINE light immediately when the diagnostic runs and fails.
• The EGR valve operation will be disabled.

Conditions for Clearing the Fault Code

The ECM will turn off the amber CHECK ENGINE light immediately after the diagnostic runs and passes.

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 diagnostic checks the reading of the EGR differential pressure sensor when the EGR valve is open. Since the EGR valve is open, the reading of the EGR differential pressure must be greater than 0. If the ECM detects a reading lower than expected with the EGR valve open, this fault code is logged.

Possible causes of this fault code include:

• A damaged EGR differential pressure sensor.
• A leaking low or high EGR differential pressure tube.
• A stuck closed EGR valve.
• A plugged or restricted EGR cooler.

Note: Do not replace the EGR differential pressure tubes for plugging unless Fault Code 2774 is active.

Refer to Troubleshooting Fault Code t05-1899