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.
Engine Control Module (ECM)/ Powertrain Control Module (Pcm)
Computerized engine controls are used to control fuel, ignition and emission control systems. Powertrain Control Module (PCM) receives input signals from various sensors and components. PCM then compares each signal with a preprogrammed parameter in its memory. Based on this comparison, output signals are then adjusted to allow vehicle to perform optimally under all operating conditions.
If an abnormality occurs in a sensor signal, PCM ignores that signal and assumes a preprogrammed value for that sensor. This allows engine to continue to run. If an abnormality occurs in PCM, fuel injectors are controlled by a back-up circuit independent of PCM system to allow minimal engine operation. If an abnormality occurs in a sensor signal, PCM grounds Malfunction Indicator Lamp (MIL) and stores DTC in erasable memory. When ignition is initially turned on, PCM supplies a ground to MIL for 2 seconds to check MIL bulb condition.
To prevent false indications, 2-trip detection method is used for HO2S, fuel metering-related, idle control system, ECT sensor, EGR system and EVAP control system self-diagnostic function. When an abnormality occurs, PCM stores DTC in memory. When same abnormality reoccurs, after ignition switch is turned off and back on, PCM informs driver by illuminating MIL. To help ease troubleshooting, 2-trip detection method is cancelled when service check connector is jumped. MIL will blink immediately when an abnormality occurs.
Civic is equipped with a 2 or 3 driving cycle detection method. In a 2 or 3 driving cycle detection method, if misfiring that increases emission is detected during 2 consecutive driving cycles, or Three-Way Catalytic (TWC) converter deterioration is detected during three consecutive driving cycles, PCM illuminates MIL. A driving cycle consists of starting engine, beginning closed loop operation and turning engine off. To help ease troubleshooting, 2 or 3 driving cycle detection method is cancelled when service check connector is jumped. MIL will blink immediately when an abnormality occurs.
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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.
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