CM871 and CM876 Electronic Control Systems, ISX and ISM Engines – FAULT CODE 1974

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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 is used to monitor the pressure inside the crankcase. The electronic control module (ECM) supplies the crankcase pressure sensor a 5 volt reference voltage. When the crankcase pressure is low, the sensor signal voltage is low. When the crankcase pressure is high, the sensor signal voltage is near the 5 volt reference voltage. The ECM monitors the crankcase pressure signal circuit voltage to calculate the pressure of the air within the crankcase.

Component Location

The crankcase pressure sensor is located in the crankcase filter assembly. The crankcase filter is located on the fuel system side of the engine. 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 engine speed is greater than 500 rpm.

Conditions for Setting the Fault Codes

The ECM detects that the crankcase pressure is greater than 20 cm H₂O [8 in H₂O].

Action Taken When the Fault Code is Active

• The ECM flashes the amber CHECK ENGINE light for 30 seconds at initial key-on when the crankcase pressure has been detected to be above 20 cm H₂O [8 in H₂O].

Conditions for Clearing the Fault Code

The ECM will turn off the flashing amber CHECK ENGINE light as soon as the crankcase pressure drops below 20 cm H₂O [8 in H₂O].

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.

Possible causes of this fault code include:

• Crankcase breather filter needs to be replaced.

Refer to Troubleshooting Fault Code t05-1974