Cummins ISB CM550 (1990-94) Fault Code: 221 PID: 108 SPN: 108 FMI: 3 Ambient Air Pressue Sensor Circuit

Circuit Description
The ambient air pressure sensor monitors atmospheric pressure and passes information to the electronic control module (ECM) through the sensor harness.

Component Location
The ambient air pressure sensor is located below the fuel transfer pump.

Shop Talk
Monitor the ambient air pressure reading with a service tool to confirm that the pressure reading matches the actual air pressure. The ambient air pressure sensor is required with 300 horsepower rated engines and specific 275 horsepower rated engines.