CM871 and CM876 Electronic Control Systems, ISX and ISM Engines – FAULT CODE 687

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Overview

ISX – Turbocharger 1 Speed Circuit SMALL | MEDIUM | LARGE

ISM – Turbocharger 1 Speed Circuit SMALL | MEDIUM | LARGE

Circuit Description

The turbocharger speed sensor is a variable reluctance speed sensor. It consists of a coil of wire and an iron core. The target on the turbocharger shaft is a ground flat in the center of the shaft. As the flat on the turbocharger shaft spins past the speed sensor, a signal is generated. The electronic control module (ECM) interprets this signal and converts it to a turbocharger speed reading.

Component Location

The turbocharger speed sensor is mounted in the center housing of the turbocharger. 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 that the turbocharger speed is detected to be less than 600 rpm for more than 1 second when the engine speed is greater than 1200 rpm.

Action Taken When the Fault Code is Active

• The ECM illuminates the amber CHECK ENGINE light immediately when the diagnostic runs and fails.
• The ECM will estimate turbocharger speed.

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.

This fault can possibly come active if the ECM senses engine speed while at the same time a turbocharger speed signal is less than 600 rpm.

Items that can fail and cause this fault code include:

• Turbocharger speed sensor.
• Engine harness.
• ECM.

This fault becomes inactive any time the speed signal from the turbocharger speed sensor returns.

If the fault occurs intermittently, look for causes of intermittent open circuit or short circuits in the turbocharger speed sensor circuit (including the speed sensor pigtail connector).

Refer to Troubleshooting Fault Code t05-687