Cummins Fault Code 687

19/11/2025

Overview

CODE

REASON

EFFECT

Fault Code: 687
PID: P103
SPN: 103
FMI: 1/18
LAMP: Amber
SRT:

Low turbocharger speed detected by the ECM.

Possible reduced engine performance.

Cummins Fault Code 687 — Turbocharger Speed Sensor Circuit

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 Engine 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.

Conditions for Running the Diagnostics

This diagnostic runs continuously when the engine is running.

Conditions for Setting the Fault Codes

The Engine Control Module (ECM) detected the turbocharger speed was less than 600 rpm for more than 1 second when the engine speed was greater than 1200 rpm.

Action Taken When the Fault Code is Active

The ECM illuminates the amber CHECK ENGINE lamp and/or the malfunction indicator lamp (MIL) immediately when the diagnostic runs and fails.

The ECM will estimate the turbocharger speed.

Conditions for Clearing the Fault Code

To validate the repair using a Diagnostic Road Test, utilize a route that incorporates both stop and go city type driving and steady state highway type driving. It may be necessary to load the unit for certain diagnostics in the ECM to run.
To validate the repair using a Chassis Dynamometer, utilize a routine that incorporates acceleration and motoring events, steady state highway type operation, and load. This will simulate normal driving and allow the diagnostics in the ECM to run.
The fault code status displayed by the recommended Cummins electronic service tool or equivalent will change to INACTIVE immediately after the diagnostic runs and passes.
The ECM will turn off the amber CHECK ENGINE lamp immediately after the diagnostic runs and passes.
For On-Board Diagnostics (OBD) engines, the ECM will extinguish the Malfunction Indicator Lamp (MIL) after three consecutive trips where the diagnostic runs and passes.
The “Reset All Faults” command in the recommended Cummins electronic service tool or equivalent can be used to clear active and inactive faults, as well as extinguish the MIL for OBD applications.

Shop Talk

Items that can cause this fault code include:

Damaged turbocharger speed sensor

Damaged engine harness

Damaged ECM.

Operating the engine at idle or high idle while stationary will not create enough load to maintain boost pressure at 1.19 times ambient pressure for 30 consecutive seconds. .

Although it is possible for a damaged ECM to be the root cause of this fault code, it is highly unlikely. ECM replacement should only be considered as a last resort, if no other repairs are successful in clearing the fault code.

In very rare cases, it has been shown that the turbocharger can cause this fault code to come active and turbocharger replacement may be the only way to clear the fault code.

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