SPN 108 - FMI 3 (Fault Code 221)

Barometric Pressure Sensor Circuit - Voltage Above Normal or Shorted to High Source

Barometric Pressure Sensor Circuit

Fault Code: 221
PID(P), SID(S): P108
SPN: 108
FMI: 3/3
Lamp: Amber

REASON: High signal voltage detected at barometric pressure circuit.

EFFECT: Engine power derate.

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

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 keyswitch is in the ON position or when the engine is running.

Conditions for Setting the Fault Codes:
The Engine Control Module (ECM) detected the barometric air pressure signal voltage was out of range high.

Action Taken When the Fault Code is Active:
• The ECM illuminates the amber CHECK ENGINE lamp and/or the malfunction indicator lamp (MIL) immediately when the diagnostic runs and fails.
• A default value for the barometric pressure reading is used.
• Engine torque will be reduced if the engine is operated for an extended period of time with this fault active.

Conditions for Clearing the Fault Code:
• To validate the repair, perform a key cycle, start the engine and let it idle for 1 minute.
• The fault code status displayed by the recommended Cummins® electronic service tool or equivalent will change to INACTIVE immediately after the diagnostic runs and passes.
• The ECM will turn off the amber CHECK ENGINE lamp immediately after the diagnostic runs and passes.
• The "Reset All Faults" command in the recommended Cummins® electronic service tool or equivalent can be used to clear active and inactive faults.

Shop Talk:
The barometric pressure sensor shares supply and return wires in the engine harness with other sensors. Opens and shorts in the engine harness can cause multiple fault codes to be active. Before troubleshooting Fault Code 221, check for multiple fault codes.
Possible causes of this fault code include:
• A short circuit to battery in the engine harness.
• An open return circuit in the engine harness
• A malfunctioning barometric air pressure sensor

Read More:
SPN 108 - FMI 4 (Fault Code 222)
SPN 1265 - FMI 4 (Fault Code 223)


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