PACCAR PX-9 CM2350 (2013-17) Fault Code:1943 PID:SID 372 SPN:3555 FMI:1 Ambient Air Density – Data Valid But Below Normal Operational Range – Least Severe Level

Reason:
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.

Effect:
Possible reduced engine performance

Circuit Description:
The engine 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.

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

Conditions for Setting the Fault Codes:
The Engine Control Module (ECM) detected the barometric air pressure reading was less than a calibratible value.

Action Taken When the Fault Code is Active:
1) The ECM logs the fault code immediately when the diagnostic runs and fails.
2) Engine torque output will be limited due to the engine operating at high altitude conditions.

Conditions for Clearing the Fault Code:
1) To validate the repair, perform a key cycle, start the engine and let it idle for 1 minute.
2) The fault code status displayed by INSITE™ electronic service tool will change to INACTIVE immediately after the diagnostic runs and passes.
3) The Reset All Faults command in INSITE™ electronic service tool can be used to clear active and inactive faults, as well as extinguish the MIL for OBD applications.

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 Causes:
1) Inactive fault codes
2) Faulty barometric pressure sensor reading
3) Faulty ECM