Computerized Engine Controls: Notes

Computerized engine control system consists of a Powertrain Control Module (PCM), various sensors (inputs), control devices and actuators (outputs), and related wiring which links system together. PCM monitors system inputs and controls system outputs accordingly to obtain optimal fuel economy and engine performance, while maintaining acceptable exhaust emission levels.

In event of an input or output failure, PCM will memorize and store information as a Diagnostic Trouble Code (DTC). DTCs can be used by technician to diagnose various driveability and emission related problems. DTCs are accessed through On-Board Diagnostics II (OBD II) Data Link Connector (DLC) with use of a Tech 1 or other OBD II compatible scan tool. DLC is located under instrument panel, accessible from driver's side.

PCM incorporates a fail-safe (limp-in) mode. If a fault occurs during vehicle operation, PCM will substitute a predetermined value and/or signal for continued operation. Driving performance will be affected, but vehicle may still be driven. When PCM detects a system fault, Malfunction Indicator Light (MIL) will flash or illuminate steadily to notify driver of a developing problem.