Pinpoint Test B: The Engine Overheats
Engine Cooling
Pinpoint Tests
Pinpoint Test B: The Engine Overheats
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 Description and Operation in the Description and Operation information.
- 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
PINPOINT TEST B: THE ENGINE OVERHEATS
WARNING: Always allow the engine to cool before opening the cooling system. Do not unscrew the coolant pressure relief cap when the engine is operating or the cooling system is hot. The cooling system is under pressure; steam and hot liquid can come out forcefully when the cap is loosened slightly. Failure to follow these instructions may result in serious personal injury.
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B1 CARRY OUT INSPECTION AND VERIFICATION
- Carry out the Inspection and Verification procedure. Inspection and Verification
- Were any concerns found?
Yes
REPAIR as needed. TEST the system for normal operation.
No
GO to B2.
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B2 CHECK FOR DTCs
- Check for DTCs P0217, P1285 or P1299.
- Is DTC P0217, P1285 or P1299 present?
Yes
GO to B3.
No
Actual engine overheating has not been verified. CHECK the engine coolant temperature gauge operation. REFER to Instrumentation, Message Center, and Warning Chimes Testing and Inspection. If any other PCM DTCs are retrieved, REFER to Electronic Engine Controls - Gasoline Engines P Codes for Electronic Engine Controls.
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B3 CHECK FOR AN AIRFLOW OBSTRUCTION
- Check the radiator or A/C condenser for an obstruction such as leaves or cardboard.
- Is an obstruction present?
Yes
REMOVE the obstruction. TEST the system for normal operation.
No
GO to B4.
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B4 CHECK THE ENGINE COOLANT LEVEL
NOTE: Allow the engine to cool before checking the coolant level.
- Ignition OFF.
- Visually check the engine coolant level in the degas bottle.
- Is the engine coolant level within specification?
Yes
GO to B5.
No
ADJUST the engine coolant level as necessary. GO to B5.
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B5 PRESSURE TEST THE ENGINE COOLING SYSTEM
- Pressure test the engine cooling system. Refer to Component Tests, Cooling System Pressure Test. Component Tests and General Diagnostics
- Does the engine cooling system leak?
Yes
REPAIR or INSTALL new components. TEST the system for normal operation.
No
GO to B6.
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B6 CHECK THE ENGINE COOLANT FOR AN INTERNAL LEAK
- Inspect the engine coolant in the degas bottle for signs of engine oil or transmission fluid.
- Is engine oil or transmission fluid evident in the coolant?
Yes
If engine oil is evident, GO to Engine System - General Information Testing and Inspection for engine diagnosis. If transmission fluid is evident, INSTALL a new radiator. REPAIR the transmission as necessary. TEST the system for normal operation.
No
GO to B7.
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B7 CHECK THE ENGINE OIL AND TRANSMISSION FLUID FOR COOLANT
- Remove the oil level indicators from the engine and the transmission.
- Is coolant evident in the oil or transmission fluid?
Yes
If coolant is in the engine oil, GO to Engine System - General Information Testing and Inspection for engine diagnosis. If coolant is in the transmission fluid, INSTALL a new radiator. REPAIR the transmission as necessary.
No
GO to B8.
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B8 CHECK THE COOLING SYSTEM FOR COMBUSTION GASES
- NOTE: Use UView(R) Combustion Leak Tester part number UVU560000-R or equivalent.
- Using a cooling system combustion gas leak tester, following the instructions supplied with the tester, check the coolant for combustion gases.
- Are combustion gases present?
Yes
GO to Engine System - General Information Testing and Inspection for engine diagnosis.
No
GO to B9.
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B9 CHECK COOLANT CONDITION
- Check the coolant for dirt, rust or contamination and check the coolant concentration.
- Is the coolant condition OK?
Yes
GO to B10.
No
FLUSH the engine cooling system. REFER to Cooling System Flushing Cooling System Flushing. TEST the system for normal operation.
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B10 CHECK THE COOLING FAN OPERATION
- Ignition OFF.
- If the vehicle is equipped with a viscous fan clutch, carry out the Fan Clutch Tests in the Component Tests information. If the vehicle is equipped with an electronically actuated fan clutch, refer to Computers and Control Systems. Component Tests and General Diagnostics
- Is the cooling fan operation OK?
Yes
GO to B11.
No
INSTALL a new cooling fan clutch. TEST the system for normal operation.
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B11 CHECK THE COOLANT PUMP OPERATION
- Start the engine.
- Allow the engine to run for 10 minutes. Place the climate control function selector in the MAX HEAT position. Feel the heater outlet hose.
- Is the heater outlet hose hot?
Yes
GO to B12.
No
INSTALL a new coolant pump. TEST the system for normal operation.
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B12 CHECK THE THERMOSTAT OPERATION
- Start the engine.
- Allow the engine to run for 10 minutes. Feel the upper radiator hose.
- Is the upper radiator hose hot?
Yes
CHECK the engine coolant temperature gauge operation. REFER to Instrumentation, Message Center, and Warning Chimes Testing and Inspection.
No
GO to B13.
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B13 VISUALLY INSPECT THE THERMOSTAT
- Carry out the Thermostat Visual Inspection in the Component Tests information. Component Tests and General Diagnostics
- Is the thermostat damaged?
Yes
INSTALL a new thermostat. TEST the system for normal operation.
No
INSTALL a new thermostat. TEST the system for normal operation. If the engine still overheats, INSTALL a new radiator. TEST the system for normal operation.
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