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.
Closed Loop Emission Control System
Closed loop emission control is a system that precisely controls air/fuel ratio, allowing use of a 3-way catalyst to reduce oxides of nitrogen, hydrocarbons and carbon monoxide.
The major components are: oxygen sensor, Electronic Control Module (ECM), controlled air/fuel ratio carburetor, and 3-way catalytic converter. This system utilizes a dashboard mounted malfunction indicator light which, for some failure modes, will inform driver of need for unscheduled maintenance.
In event of system malfunction, "Check Engine" light will come on and remain on as long as fault continues and engine is running. The ECM incorporates a diagnostic program which will assist in diagnosing closed loop control system malfunction. When activated, diagnostic program will flash a code through "Check Engine" light, which isolates source of malfunction.
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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.