Normal Operation

The engine cooling system functions to maintain engine temperatures during operation. Correct coolant flow through the engine, radiator and remainder of cooling system passages and components is essential to maintaining a correct engine temperature.

Engine coolant flows primarily from the engine to the radiator circuit and back to the coolant pump. Coolant is sent from the coolant pump through the engine block and cylinder heads. A separate circuit from the engine also feeds the heater core with coolant. The coolant pump is operated by engine rotation through a pulley which is driven by the accessory drive belt to circulate the coolant. The coolant thermostat is a control valve actuated by coolant temperature. When the thermostat is closed, coolant flow bypasses the radiator circuit and returns to the coolant pump. When the thermostat is opened, coolant flows through the radiator circuit in order to transfer engine-generated heat to the outside air.

Engine overheating generally occurs when there is a disruption in the ability to control either coolant flow at the proper rate, the inability to transfer heat from the engine through the coolant (including low coolant) or an inability to transfer engine-generated heat to the outside air through the radiator.

For engine specific information, refer to Engine Cooling  in the Description and Operation portion of this section.

• DTC P0217 (Engine Coolant Over Temperature Condition) - Indicates an engine overheat condition was detected by the Cylinder Head Temperature (CHT) sensor.
• DTC P1285 (Cylinder Head Over Temperature Condition) - Indicates an engine overheat condition was sensed by the CHT sensor.
• DTC P1299 (Cylinder Head Over Temperature Protection Active) - Indicates an engine overheat condition was detected by the CHT sensor. A failure mode effects management strategy called fail-safe cooling was activated to cool the engine.

This pinpoint test is intended to diagnose the following:

• Low coolant level
• External engine coolant leak
• Airlock in system
• Heater core
• Pressure relief cap installation
• Restricted airflow through the A/C condenser or radiator
• Internal engine coolant leak
• Transmission fluid cooler leak
• Coolant condition/concentration
• Accessory drive components
• Non-OEM engine enhancement components
• Cooling fan
• Electronic cooling fan clutch - 6.2L engines
• Mechanical cooling fan clutch - 6.8L engines
• Engine Coolant Temperature (ECT) gauge
• Cylinder Head Temperature (CHT) sensor
• Thermostat
• Coolant pump
• Coolant flow restriction