Engine Control Module: Description and Operation

System Diagram:

PURPOSE
The Powertrain Control Module (PCME) is the central processor (computer) for all engine management functions. The system maintains an air/fuel mixture as close as possible to ideal stoichiometric ratio, maintaining good driveability and reduced emissions. PCME monitors various sensors mounted on the engine and uses this information to modify fuel injector duration ("ON" time), regulate ignition timing, and operate certain emission control devices.

FAIL-SAFE MODE
To provide a margin of safety by maintaining driveability in the event of certain system failures, PCME has a fail-safe mode of preprogrammed values. PCME output will automatically switch to fail-safe mode if a fault is detected in any of these components and/or systems:

^ Airflow meter
^ Atmospheric pressure sensor
^ Feedback system
^ Intake air thermosensor (in airflow meter)
^ Intake air thermosensor (in dynamic chamber)
^ Oxygen sensor
^ Throttle sensor
^ Water thermosensor

ON-BOARD DIAGNOSTICS
PCME incorporates self-diagnostic capability monitored via a dash mounted malfunction indicator lamp (MIL). When the system detects a fault in a monitored component and/or circuit, the lamp will light ("CHECK") and stay on (while the engine is running). To extract codes, the technician can either utilize a "Scan" tool or cause the MIL to display codes by grounding the data link connector in the engine compartment.

NOTE: PCME constantly monitors input devices for malfunctions. However, it only checks for output device faults during a three second period after the ignition is switched "ON" and data link connector is grounded.