Cummins ISX12 CM2250 (2010-12) Fault Code: 1943 PID: SPN: 3555 FMI: 17 Ambient Air Density- Data Valid But Below Normal Operational Range- Least Severe Level

Circuit Description
The engine electronic control module (ECM) monitors the ambient air pressure using either an ambient air pressure sensor or a combination turbocharger compressor intake pressure/temperature sensor. These sensors respond to pressure changes in the atmosphere, which occur based on the elevation where the engine is currently operating. This pressure sensor has a 5 volt supply circuit, a sensor signal voltage, and a return circuit. The ambient air or compressor intake pressure sensor provides a signal to the ECM on the pressure sensor signal circuit. This sensor signal voltage changes based on the pressure of the atmosphere. The ECM will detect a low signal voltage when the vehicle is operating at high altitudes. The ECM will detect a high signal voltage when the vehicle is operating at sea level altitudes.

Component Location
The barometric pressure sensor is mounted on the main branch of the engine harness near the ECM. The turbocharger compressor intake pressure sensor is located just prior to the inlet to the turbocharger. Use the engine wiring diagram to determine which sensor the engine is equipped with.

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

Conditions for Setting the Fault Codes
The ECM detects that the ambient air pressure reading is lower than a calibratible value.

Action Taken When the Fault Code is Active
The ECM logs the fault code immediately when the diagnostic runs and fails.
Engine torque output will be limited due to the engine operating at high altitude conditions.
Conditions for Clearing the Fault Code
To validate the repair, start the engine and let it idle for 1 minute.
The fault code status displayed by INSITE? electronic service tool will change to INACTIVE immediately after the diagnostic runs and passes.
The Reset All Faults command in INSITE? electronic service tool can be used to clear active and inactive faults.

Shop Talk
When the engine has been operated in a high altitude location, this fault code is logged. This fault code is for information only and no repairs are necessary. The engine can possibly be derated when operating in the high altitude location to protect the turbocharger and engine from excessively high exhaust temperatures. The derate limits the torque output of the engine to keep the temperatures below the maximum temperature limits.

Note: This fault code will most likely not be active with no load in the shop. The engine must be under the same operating condition (altitude and temperature) at the time that it had originally logged.

Possible Cause:
1) Barometric Pressure Sensor failure
2) ECM calibration