For 1990-2009 cars

Since the BCM is the master on the Class II link and the SDM is on every vehicle, these controllers should be communicated with first since they may help to determine potential serial data link errors.

This chart continues establishing communications with each of the applicable modules on the vehicle.

If communications can be established with each control module, and there are no DTCs associated with any of them, the vehicle on-board diagnostics system check is complete. If no DTCs were detected, the next step is to refer to the symptom section for the system/sub-system related to the customer complaint.