CM871 and CM876 Electronic Control Systems, ISX and ISM Engines – FAULT CODE 1843

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Overview

ISX – Crankcase Pressure Sensor SMALL | MEDIUM | LARGE

ISM – Crankcase Pressure Sensor SMALL | MEDIUM | LARGE

Circuit Description

The crankcase pressure sensor monitors the pressure inside the crankcase gas filter assembly. If the pressure inside the crankcase filter assembly reaches a maximum level, a fault code will be logged indicating that maintenance is required on the crankcase filter.

Component Location

The crankcase pressure sensor is located in the crankcase filter assembly. 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 electronic control module (ECM) detects that the crankcase pressure signal voltage is greater than 4.8 VDC for more than 1 second.

Action Taken When the Fault Code is Active

• The ECM illuminates the amber CHECK ENGINE light immediately when the diagnostic runs and fails.
• A default value for the crankcase pressure reading is used.

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, 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.

The crankcase pressure sensor shares supply and return wires in the engine harness with other sensors. Opens and shorts in the engine harness can cause multiple fault codes to be active. Before troubleshooting, check for multiple fault codes.

Possible causes of this fault code include:

• Open return circuit in the engine harness, connectors, or sensor.
• Signal wire shorted to sensor supply or battery voltage.

Refer to Troubleshooting Fault Code t05-1843