Coolant Temperature Override (CTO) Switch
Coolant temperature override (CTO) switch is located in coolant passage of intake manifold, or at right rear corner of intake manifold near EGR valve on V8 engines, or at left front side of cylinder block on 6-cylinder engines.
Inner port of switch is connected to EGR spark port on carburetor and outer port is connected to EGR valve, or TVS. Switch opens at 115°F (46°C) for 6-cylinder and V8 engines. Below these temperatures, no EGR is possible.