CM871 and CM876 Electronic Control Systems, ISX and ISM Engines – FAULT CODE 689 (ISX)

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Overview

ISX – Engine Crankshaft Speed/Position SMALL | MEDIUM | LARGE

Circuit Description

The electronic control module (ECM) provides a 5 VDC supply to the engine crankshaft speed/position sensor on the sensor supply circuit. The ECM also provides a ground on the sensor return circuit. The crankshaft speed/position sensor provides a signal to the ECM on the crankshaft speed/position sensor signal circuit. This sensor generates a signal to the ECM as the crankshaft speed indicator ring passes the sensor. The ECM interprets this signal into an engine speed reading and determines engine position.

Component Location

The engine speed sensor is located on the side of the front gear housing on the intake 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 is running.

Conditions for Setting the Fault Codes

The ECM detects a loss of the crankshaft speed/position sensor for more than one second.

Action Taken When the Fault Code is Active

• The ECM illuminates the amber CHECK ENGINE light immediately when the diagnostic runs and fails.
• The camshaft speed sensor is used to provide engine speed and position information to the ECM.

Conditions for Clearing the Fault Code

The ECM will turn off the amber CHECK ENGINE light immediately after the ECM detects a valid signal from the crankshaft speed/position sensor.

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.

This fault is logged when the ECM does not receive a valid engine speed signal.

Causes of this fault include:

• Open or short circuit of the +5 volt supply, signal, or return wire in the engine harness.
• Damaged or failed engine speed sensor.

Refer to Troubleshooting Fault Code t05-689