Test 1: Scan Tool Will Not Communicate With Class 1 Serial Data Line

For class 1 serial data line diagnosis, see Fig 1 and Fig 2 .

Fig 1: Class 1 Serial Data Line Diagnostic Flowchart (1 Of 2)

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Fig 2: Class 1 Serial Data Line Diagnostic Flowchart (2 Of 2)

Courtesy of GENERAL MOTORS CORP.