Fail-Safe Cooling Strategy

The fail-safe cooling strategy is activated by the PCM only in the event that an overheating condition has been identified. This strategy provides engine temperature control when the cylinder head temperature exceeds certain limits. The cylinder head temperature is measured by the cylinder head temperature (CHT) sensor. For additional information about the CHT sensor, refer to ENGINE CONTROL COMPONENTS .

A cooling system failure such as low coolant or coolant loss could cause an overheating condition. As a result, damage to major engine components may occur. Along with a CHT sensor, the fail-safe cooling strategy is used to prevent damage by allowing air-cooling of the engine. This strategy allows the vehicle to be driven safely for a short period of time when an overheat condition exists.

The engine temperature is controlled by varying and alternating the number of disabled fuel injectors. This allows all cylinders to cool. When the fuel injectors are disabled, their respective cylinders work as air pumps, and this air is used to cool the cylinders.

On the hybrid vehicle, the PCM provides a fail-safe cooling status information to the instrument cluster (IC) through the controller area network (CAN). The PCM sends a CAN message signal to the cluster indicating what fail-safe cooling mode the vehicle is in. There are three levels of this message; normal operating mode, fail-safe mode one, and fail-safe mode 2. The cluster turns the red temperature indicator off if normal operating mode is received, turns the red temperature indicator on if it receives a fail-safe mode 1 message, and it flashes the red temperature indicator if it receives a fail-safe mode 2 message. During fail-safe mode 1 the PCM sets DTC P1285 and during fail-safe mode 2 the PCM sets DTC P1299.

NOTE: The IC red temperature indicator is also used by the motor electronics cooling system loop and may be illuminated by an over temperature condition in that subsystem. The motor electronics cooling system loop includes the generator, DC/DC converter, and the traction motor. The motor electronics cooling system loop also contains a motor electronic coolant temperature (MECT) sensor and motor electronics coolant system (MECS) pump to circulate the coolant. For additional information on the MECT sensor and the MECS pump, refer to ENGINE CONTROL COMPONENTS .