Serial Data
WARNING: This page is about a different car, the 2003 Pontiac Vibe. However, it is still accessible from the selected car via links, so may be relevant.
PCM is equipped with a serial data line. Serial data is a stream of electrical impulses which can be interpreted by special testers or other control modules. When the ignition is turned on, each module sends a state of health message to the other modules using the serial data line. Ensuring the modules are working properly. If a module stops communicating, other control modules expecting information from that module will set a DTC. Serial data and codes must be accessed using a scan tool connected to the Data Link Connector (DLC). Update intervals and information contained within the data stream vary with model application.