Scan Tool Does Not Communicate With Class 2 Device

Modules connected to the Class 2 serial data circuit monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules. Connecting a scan tool to the DLC allows communication with the modules for diagnostic purposes. Diagnostic Trouble Codes (DTC) may be set due to this symptom and during this diagnostic procedure. Complete the diagnostic procedure in order to ensure all the DTCs are diagnosed and cleared from memory. For diagnostic procedures, see DTC U1000 & U1255: CLASS 2 COMMUNICATION MALFUNCTION  under DIAGNOSTIC PROCEDURES.