Which device prevents EGR operation during cold engine conditions?

The thermal vacuum switch is designed to prevent EGR (Exhaust Gas Recirculation) operation during cold engine conditions by controlling the flow of vacuum to the EGR system. When the engine is cold, the thermal vacuum switch remains closed, which effectively blocks the vacuum that would normally enable the EGR valve to open. This is important because EGR is not effective or necessary until the engine reaches a certain temperature, and introducing exhaust gases into the intake during cold operation can lead to poor combustion, increased emissions, and potential engine performance issues. As the engine warms up and reaches the appropriate temperature, the thermal vacuum switch opens, allowing vacuum to reach the EGR valve and enabling its operation.

Other devices listed, such as the EGR valve position sensor, EGR vacuum solenoid valve, and EGR vacuum regulator, play roles in monitoring, controlling, or regulating EGR flow, but they do not prevent EGR operation during cold conditions specifically like the thermal vacuum switch does.