Cummins ISX CM870 (2003-06) Fault Code: 1943 PID: SPN: 3555 FMI: 1/17 Ambient Air Density – Data Valid But Below Normal Operational Range – Least Severe Level. Engine torque has been reduced because the vehicle was operating at a high altitude condition.

The most common cause of this fault code is high altitude. The fault code can also be caused by extreme ambient air temperatures. This derate can be viewed in the INSITE? electronic service tool, User Fueling State, as Air Density Limit State.

NOTE: The engine must be loaded to trip this fault code in the shop. The engine must be under the same operating conditions (altitude and temperature) at the time that it had originally logged.

Possible repair:

1)Replace the barometric pressure sensor.
2)Calibrate the ECM, use the INCAL? DVD with the proper calibration software phase.