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.
Stop Light Switch Circuit: Description
When the brake pedal is depressed, the stop light switch turns on and transmits an STP signal to the ECM. Upon receipt of the STP signal, the ECM determines that the brakes have been applied. The signal voltage level is the same as that of the voltage which is applied to the stop lights. In addition, the STP signal is used to control the fuel cut-off engine speed. Therefore, the fuel cut-off engine speed is slightly reduced when the vehicle is braking.
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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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