CM850 Electronic Control System – FAULT CODE 687 (ISB/QSB Automotive or Industrial Application)

Turbocharger Speed Sensor – Below Normal Operating Range


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

Turbocharger number 1 speed low – warning level. Low turbocharger speed detected by the ECM.

Engine power derate. The ECM uses estimated turbocharger speed.

Turbocharger Speed Sensor Circuit

Circuit Description

The electronic control module (ECM) provides +5 VDC to the turbocharger speed sensor signal pin. Circuitry inside the turbocharger speed sensor detects the movement of the turbocharger compressor blades and produces a speed signal. This signal is used by the ECM for engine controls.

Component Location

The turbocharger speed sensor is located in the turbocharger compressor housing. Refer to Procedure 100-002 for a detailed component location view.

Shop Talk

This fault will become active if the engine is running and the ECM detects boost pressure and engine speed but no turbocharger speed signal. Possible causes of this fault:

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

This fault becomes inactive at key-on or any time the speed signal from the turbocharger speed sensor returns. If the fault occurs intermittently, Fault Code 2345 can also be in the ECM memory. 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

Last Modified:  08-Jul-2010