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.
Electronic Control Module (ECM): Run
When engine speed is greater than 400 RPM, ECM operates in "open loop". In "open loop", ECM calculates injector pulse width based upon coolant temperature and Manifold Absolute Pressure (MAP). Engine will remain in "open loop" operation until O2 sensor reaches operating temperature, coolant temperature reaches preset temperature, and a specific period of time has elapsed after engine starts. When all these conditions are met, ECM operates in "closed loop". In "closed loop", ECM controls injector pulse width based upon O2 sensor signals (in addition to other input parameters) to maintain as close to a 14.7:1 air/fuel mixture as possible.
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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.