CM871 and CM876 Electronic Control Systems, ISX and ISM Engines – FAULT CODE 629

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Overview

ISX and ISM Electronic Control Module (ECM) SMALL | MEDIUM | LARGE

Circuit Description

The pressure differential over the compressor seal is a calculated value derived from the difference between charge pressure and crankcase pressure.

Component Location

None.

Conditions for Running the Diagnostics

This diagnostic runs continuously when the keyswitch is in the ON position and the engine is running.

Conditions for Setting the Fault Codes

The electronic control module (ECM) detects that the pressure differential over the compressor seal exceeds the recommended maximum.

Action Taken When the Fault Code is Active

• The ECM registers the fault code and illuminates the amber CHECK ENGINE light after the problem has persisted for 5 minutes.
• An engine torque derate will occur as soon as the fault code goes active.

Conditions for Clearing the Fault Code

Once the ECM detects the pressure differential over the compressor seal has fallen below the maximum threshold, the fault code will go inactive.

Shop Talk

Verify the ECM calibration is correct. Check the calibration revision history found on QuickServe™ Online for applicable corrections to the calibration stored in the ECM. Refer to Procedure 019-032 (ECM Calibration) in Section 19.

Possible causes of this fault code include:

Crankcase filter needs to be replaced.

• If the crankcase filter is being replaced frequently for this fault code, reference the Crankcase Coalescing Filter – Frequent Replacement troubleshooting symptom tree.
• For ISM engines, reference the ISM, ISMe, and QSM11 Service Manual, Bulletin 3666322.
• For ISX engines, reference the Signature™, ISX, and QSX15 Service Manual, Bulletin 3666239.

Air intake filter needs to be replaced.

• Refer to Procedure For ISM engines, 010-031 (Air Intake Restriction) in Section 10 of the ISM, ISMe, and QSM11 Service Manual, Bulletin 3666322.
• Refer to Procedure For ISX engines, 010-031 (Air Intake Restriction) in Section 10 of the Signature™, ISX, and QSX15 Service Manual, Bulletin 3666239.

A plugged or restricted crankcase ventilation system.

• Check the tube between the engine and the coalescing filter.
• Check the draft tube going from the coalescing filter to the atmosphere or intake manifold.
• Consider the working environment. Ice, snow, or mud can temporarily block the tube and then fall away.

Complete the entire troubleshooting tree whether Fault Code 629 is active or inactive.

• If a problem is found in the early steps, the troubleshooting tree should still be completed.

Refer to Troubleshooting Fault Code t05-629