Cummins ISB4.5 CM2150 Fault Code: 686 PID: 103 SPN: 103 FMI: 2 Turbocharger 1 Speed – Data Erratic, Intermittent, or Incorrect.

Posted by PerDiezel Solutions on January 20, 2026

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.

Conditions for Running the Diagnostics
This diagnostic runs continuously when the engine is running.

Conditions for Setting the Fault Codes
The ECM detects a turbocharger speed that is greater than the speed that is physically achievable by the turbocharger.

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 the turbocharger speed.

Conditions for Clearing the Fault Code
-To validate the repair, start the engine and let it idle for 1 minute
-The ECM will turn off the amber CHECK ENGINE light immediately after the ECM detects a valid turbocharger speed, and the diagnostic runs and passes.

Shop Talk
Usually this fault code indicates a faulty turbocharger speed sensor or incorrect speed signals from the sensor.

Possible Causes
-Turbocharger speed sensor
-Engine harness
-ECM power supply or grounds
-Electronic vehicle accessories which emit excessive electromagnetic interference.

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).
Look for sources of electronic noise such as poorly installed vehicle electronic components.
Be sure that the vehicle chassis grounds are in good condition.
Be sure that the ECM power supply and ground circuits are in good condition and that this power supply is not shared with other vehicle electronics.

Cummins ISB4.5 CM2150 Fault Code: 649 PID: SID 115 SPN: 1378 FMI: 11 Engine Oil Change Interval – Condition Exists.

Cummins ISB4.5 CM2150 Fault Code: 598 PID: 167 SPN: 167 FMI: 1 Electrical Charging System Voltage – Data Valid But Below Normal Operating Range – Most Severe Level.

Cummins ISB4.5 CM2150 Fault Code: 597 PID: 167 SPN: 167 FMI: 1 Electrical Charging System Voltage – Data Valid But Below Normal Operating Range – Moderately Severe Level.

Cummins ISB4.5 CM2150 Fault Code: 596 PID: 167 SPN: 167 FMI: 0 Electrical Charging System Voltage – Data Valid But Above Normal Operating Range – Moderately Severe Level.

Cummins ISB4.5 CM2150 Fault Code: 585 PID: SID 39 SPN: 677 FMI: 4 Starter Relay Driver Circuit – Voltage Below Normal or Shorted to Low Source.

Cummins ISB4.5 CM2150 Fault Code: 584 PID: SID 39 SPN: 677 FMI: 3 Starter Relay Driver Circuit – Voltage Above Normal or Shorted to High Source.

WARNING!