On my channel are two videos produced on March 1, 2020 that reviews 4 brand new Walthers Mainline GP9s. All came equipped with ESU Loksound Essential Sound Unit decoders. Out of the package 3 of the 4 locomotives purchases randomly engaged the dynamic brakes after about 10 seconds of running. This video shows the problem and how to rectify it.
If you do not have a LokProgrammer, you can disable the dynamic brakes using your DCC system/programming track by changing the following CVs:
CV38 = 0
CV216 = 0
CV207 = 0
CV232 = 0
