Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Computerized Engine Controls: Notes
Computerized engine control system consists of a Powertrain Control Module (PCM), various input sensors, controlled devices and actuators (outputs) and related wiring which links system together. PCM monitors engine and vehicle functions while controlling (outputs) engine fuel control, Ignition Control (IC), automatic transaxle shift functions, cruise control enable, generator, Evaporative Emission Purge (EVAP), Exhaust Gas Recirculation (EGR), A/C clutch operation and cooling fan operation.
PCM performs On-Board Diagnostics-II (OBD-II) diagnostic tests of emission related systems. OBD-II diagnostics ensure emission systems operate correctly and have not degraded to a point where vehicle emissions exceed local emission standards.
In the 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 Data Link Connector (OBD-II DLC) with use of an OBD-II compatible scan tool. OBD-II DLC is located under instrument panel, accessible from driver's side. See Fig 3 or Fig 13
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. For location of MIL, see Fig 2 or Fig 13 .
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.