Technician Handbook Air Conditioning for Collision Repair Techstream Health Check The A/C ECU stores Diagnostic Trouble Codes (DTCs) in response to most faults in its sensors, actuators and circuits. Performing a Health Check retrieves all active DTCs. An active code for the air conditioning system can lead you directly to a problem area. The Repair Manual lists every DTC along with details that will help you isolate the cause. NOTE On some vehicles, Techstream may not be able to retrieve DTCs from the A/C ECU. On these vehicles, DTCs must be retrieved using the Check Mode Procedure. 20 Collision Repair & Refinish Training