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GM/Detroit 6.5L – Engine Management – POWERTRAIN CONTROL MODULE (PCM) OVERVIEW

The Powertrain Control Module (PCM), located in the passenger compartment (figure 5-1), controls the EFI system.

Internally, the PCM is programmed with calibration infor­mation specific to the vehicle. This program tells the PCM what the normal operating parameters are for fuel deliv­ery, timing, emissions control, and transmission control.

Externally, the PCM is hard-wired to numerous sensors, known as “inputs,” as well as to solenoids, relays and indicator lamps, known as “outputs.” The full roster of 6.5L EFI V8 PCM inputs and outputs are shown in figure 5-2.

The PCM constantly receives and interprets information from the inputs. It processes this information and com­ pares it to the nominal, or normal, values with which it is programmed. The PCM then either sends or inhibits electrical responses to output devices in order to control fuel delivery, timing, and other emission control systems.

When input data doesn’t correspond to PCM parameters, or when output devices don’t respond as they should, one or more Diagnostic Trouble Codes (DTC) can be set. These codes are stored in the PCM memory. Under many code conditions, the PCM will substitute default values that provide the driver with vehicle operation.

Using either the on-vehicle Data Link Connector (DLC) or a “Scan” tool, a technician can access stored codes in order to determine the causes of a driveability condition. Codes are designed so that each one relates to a specific component or system. By using the a code’s corresponding diagnostic trouble-tree chart located in Section 3 of the diesel Driveability and Emissions Service Manual, a technician can systematically pinpoint and correct the condition. “Scan” tool usage and code reading are addressed in detail in section 6 of this book.

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