Fail Safe Cooling: Notes
WARNING: This page is about a different car, the 2018 Lincoln MKC. However, it is still accessible from the selected car via links, so may be relevant.
A strategy called Fail Safe Cooling is built into the PCM that will control the engine if it starts to overheat.
Fail Safe Cooling has two modes: A 'Closed Loop' mode that relies on CHT sensor and an 'Open Loop' mode that relies on ECT sensor. When the engine starts to overheat, the decision to go into closed loop or open loop mode is made based on sensor availability and sensor failures. Closed loop mode takes priority over open loop. The reason is that a good CHT sensor is able to reliably track engine block temperature at all times, while the ECT sensor will fail to do so when the engine coolant is dumped.