Cummins ISB CM850 (2003-06) Fault Code: 687 (ISC) PID: 103 SPN: 103 FMI: 1 Turbocharger Number 1 Speed Low – Data Valid but Below Normal Operational Range – Moderately Severe Level. Low turbocharger speed detected by the ECM.

This fault may come active if the electronic control module (ECM) senses boost pressure and engine speed while at the same time a turbocharger speed signal is not present.

Items that can fail and cause this fault code include:

1)Turbocharger speed sensor
2)Engine harness
3)Barometric pressure sensor
4)Intake manifold pressure sensor
5)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).

Possible repairs:

1)Repair or replace the damaged connector or turbocharger speed sensor.
2)Repair or replace the engine harness connector.