CM871 and CM876 Electronic Control Systems, ISX and ISM Engines – FAULT CODE 1844

Crankcase Pressure Circuit – Voltage Below Normal, or Shorted to Low Source


Fault Code: 1844
PID: P101
SPN: 101
FMI: 4/4
LAMP: Amber

Crankcase Pressure Circuit – Voltage Below Normal, or Shorted to Low Source. Low signal voltage detected at the crankcase pressure circuit.

No engine protection for high crankcase pressure.

ISX – Crankcase Pressure Sensor
ISM – Crankcase Pressure Sensor

Circuit Description

The electronic control module (ECM) provides a 5 volt supply to the crankcase pressure sensor on the sensor supply circuit. The ECM also provides a ground on the sensor return circuit. The crankcase pressure sensor provides a signal to the ECM on the crankcase pressure sensor signal circuit. This sensor signal voltage changes based on the pressure in 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 ECM detects that the crankcase pressure signal voltage is less than 0.2 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:

  • Signal circuit open or shorted to ground, in the engine harness or sensor.
  • Supply wire open or shorted to ground.

Refer to Troubleshooting Fault Code t05-1844

Last Modified:  09-Jul-2010