Cummins ISB4.5 CM2150 Fault Code: 295 PID: 108 SPN: 108 FMI: 2 Barometric Pressure – Data Erratic, Intermittent, or Incorrect.

Circuit Description
The barometric air pressure sensor responds to pressure changes in the atmospheric pressure. The pressure changes occur based on elevation where the engine is presently operating. The barometric air pressure sensor has a 5 volt supply circuit, a sensor signal voltage, and a return circuit.

The electronic control module (ECM) provides a 5 volt supply to the barometric air pressure sensor on the sensor supply 1 circuit. The ECM also provides a ground on the sensor return circuit. The barometric air pressure sensor provides a signal to the ECM on the barometric air 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 consists of two parts. One part runs when the keyswitch is initially turned on before the engine is started.

The other part runs continuously when the engine is operating.

Conditions for Setting the Fault Codes
The ECM detects that the barometric pressure reading is higher or lower than the other absolute pressure sensors on the engine, or an in-range malfunction of the sensor has been detected.

Action Taken When the Fault Code is Active
-The ECM illuminates the amber CHECK ENGINE lamp and/or the MIL immediately after the diagnostic runs and fails.
-Engine torque will be reduced.
-A default value is used for the barometric pressure reading.

Conditions for Clearing the Fault Code
-This fault code can not be cleared with INSITE™ electronic service tool.
-To validate the repair, start the engine and let it idle for 1 minute.
-The ECM will turn off the amber CHECK ENGINE lamp and/or MIL immediately after the diagnostic runs and passes.
-Use INSITE™ electronic service tool to verify the fault code is inactive.
-The inactive fault code will be cleared from the memory after 9600 hours of engine operation without a reoccurrence.

Possible Causes
-Stuck in-range barometric pressure sensor reading
-High resistance in the barometric pressure sensor signal or return lines.