CM871 and CM876 Electronic Control Systems, ISX and ISM Engines – FAULT CODE 556

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Overview

ISX – Crankcase Pressure Sensor Circuit SMALL | MEDIUM | LARGE

ISM – Crankcase Pressure Sensor Circuit SMALL | MEDIUM | LARGE

Circuit Description

The pressure inside the crankcase is measured by the crankcase pressure sensor. When the crankcase pressure sensor determines that the crankcase pressure is higher than normal, this fault code is logged.

Component Location

The crankcase pressure sensor is located in the crankcase filter. The crankcase filter is located on the fuel system side of the engine. Use the following procedure for a detailed component location view. Refer to Procedure 100-002 in Section E.

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 a calibratible limit.

Action Taken When the Fault Code is Active

• The ECM illuminates the red STOP ENGINE light when the crankcase pressure limit is exceeded.
• The engine torque output will be reduced to protect the engine from excessive crankcase pressure.

Conditions for Clearing the Fault Code

The ECM will turn off the red STOP ENGINE light as soon as the crankcase pressure drops below a calibratible limit.

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.

Possible causes of this fault code include:

• Crankcase filter needs to be replaced.
• Frozen crankcase breather filter.
• Frozen inlet tube to the crankcase breather filter housing.
• Frozen outlet tube from the crankcase breather filter housing.
• Frozen inside the crankcase breather filter housing.

If the crankcase filter is being replaced frequently for this fault code, refer to the Crankcase Coalescing Filter – Frequent Replacement troubleshooting symptom tree.

• For ISM engines, refer to the ISM, ISMe, and QSM11 Service Manual, Bulletin 3666322.
• For ISX engines, refer to the Signature™, ISX and QSX15 Service Manual, Bulletin 3666329.

Refer to Troubleshooting Fault Code t05-556