Coolant Temperature Override Valve

The CTO valve is located on the left rear corner of the engine block. A manifold vacuum hose is attached to the CTO. Manifold vacuum should be present at the air control valve when coolant temperature is less than 160°F. No vacuum should be present if coolant temperature is above 160°F. The CTO is connected to the air valve by a hose. The CTO used on California vehicles routes all air system pressure to air injection manifold until engine coolant reaches 149°F.