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Several vacuum-operated engine functions are only implemented when the engine is warm. For example, smog control systems like the EGR valve require the engine to be hot before they can effectively operate. A thermal vacuum switch only allows vacuum to pass through the switch when the correct temperature has been reached. A valve inside opens, and the vacuum, or negative pressure, is able to move through. If the thermal vacuum switch is plugged or stuck, the vacuum passage will not switch and the system it controls will not operate. If the vacuum switch is leaking, there may not be enough vacuum to control all the vacuum-operated systems in the car.
Thermal vacuum switches do not require maintenance and rarely fail. If you believe there is a vacuum problem in your vehicle, have one of our expert mechanics diagnose it.
A thermal vacuum switch failure can cause a loss of vacuum to several components, not just the affected system that particular switch controls. Safety systems such as power brakes can be affected, so a failed thermal vacuum switch should be addressed immediately.