The Active Exhaust System (AES) was introduced in 2007 on the Big Twin models for on-US markets, including England and Australia. It is an ECM-controlled electric motor to open or close a butterfly valve in the exhaust system to meet the exhaust noise standards.
Aftermarket exhaust systems regularly do neither work with butterflies nor provide any means to mount this motor. If the harness plug for this motor is left empty, the MIL warning is activated and an error code is saved in the ECU. The AES bypass avoids both.