EGR CTO Switch

This switch is located in the coolant passage on the bottom of the intake manifold (4-cylinder), at the left side of the cylinder block (6-cylinder), or next to the oil filler tube on the intake manifold (V8).

The inner port ("S") is connected to the EGR port at the carburetor. The outer port ("E") connects to the EGR valve or TVS. When coolant temperature is low, there is no vacuum signal to the EGR system. EGR operation will begin when coolant temperature reaches 160°F (Yellow valve), 115°F (Black valve) or 85°F (White valve).