TM 9-2320-364-103-20 Table 3-1. Troubleshooting - CONT.MalfunctionTest or InspectionCorrective ActionAIR SYSTEM (CONT).2.TRAILER BRAKES DO NOT APPLY WHEN SERVICE BRAKE PEDAL OR PARKING BRAKE IS USED.Step 1. Check to make sure that TRAILER AIR SUPPLY control (1) is pushed in (ON position).Step 2. Check to make sure that service (2) and emergency air hoses (3) are securely and correctly connected (TM 9-2330-385-14).Step 3. Check to make sure trailer air reservoir petcocks are closed.·Close all petcocks.·If problem still exists, notify Unit Maintenance.