EGR Thermal Vacuum Switch

EGR-TVS closes to prevent EGR operation when engine coolant temperature is less than 85°F (29°C). This improved cold engine driveability. When coolant temperature increases to greater than 85°F (29°C), TVS opens to allow vacuum to be directed to EGR valve.

Fig 1: Sectional View of Negative Backpressure EGR Valve

Courtesy of GENERAL MOTORS CORP.