15521 - CUSTOMER ADVISORY LETTER. THIS LETTER IS BEING SENT TO BRING TO THE CUSTOMER'S ATTENTION FEATURES THAT ARE COVERED IN THE VEHICLE'S OWNER MANUAL IN SITUATIONS WHERE THE CUSTOMER VEHICLE SIDE DOORS WILL NOT OPEN FROM INSIDE AND OUTSIDE THE VEHICLE DUE TO LOW OR NO BATTERY VOLTAGE. DEALERS ARE ALSO INSTRUCTED THAT IN CORRELATION WITH THIS CUSTOMER ADVISORY LETTER, A WEB-BASED TRAINING COURSE WILL BE REQUIRED FOR ALL CADILLAC AND CHEVROLET SALES CONSULTANTS, SALES MANAGERS, SERVICE CONSULTANTS, SERVICE MANAGERS, AND FIELD STAFF BEGINNING Q1 2016 VIA THE GM CENTER OF LEARNING.