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.
DECEL Throttle Modulator: Description
The decel throttle modulator system, used on some Heavy Duty emissions models, keeps the throttle valves open slightly during deceleration to help reduce emissions. System consists of a speed sensor, solenoid vacuum valve, throttle modulator on throttle linkage, ported vacuum switch, and electrical wiring and vacuum hoses. The system is electrically connected to the "B+" terminal of the ignition switch and to the "+" terminal of ignition coil. See Figure.
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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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