Malibu V6-191 3.1L VIN M SFI (1997)
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Powertrain Control Module (PCM)
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Sensing and Diagnostic Module (SDM) - Supplemental Inflatable Restraint System (CKT 800 UART)
A combination of inputs from these components, other sensors and switches go to the computers either as discrete/analog inputs, communicated on the
communications link (called the Data Line (circuit 1807 Class 2, or circuit 800 UART) and Serial Peripheral Interface (SPI) [circuit 1321, circuit 1322
and circuit 1323]) to other computers.
Visual Inspection
One of the most important checks, which must be done before any diagnostic activity, is a careful visual inspection of suspect wiring and components.
This can often lead to fixing a malfunction without further steps. Inspect the battery hydrometer (green eye) to assure the Battery is not discharged.
Inspect all vacuum and electrical circuits for pinches, cuts or disconnects. This visual inspection is very important. It must be done carefully and
thoroughly.
