Pinpoint Test B: The Engine Overheats
Engine Cooling
Pinpoint Test B: The Engine Overheats
Normal Operation
The engine cooling system maintains 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. From the coolant pump, coolant is sent through the engine block and cylinder heads. 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 2.5L engine coolant pump is operated by engine rotation through a pulley driven by the accessory drive belt. The 3.0L coolant pump is operated by a V-ribbed belt driven by a pulley attached to the camshaft. The 3.5L coolant pump is operated through a sprocket driven by the timing chain. 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 correct 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.
- DTC P0217 (Engine Coolant Overtemperature Condition)- Indicates an engine overheat condition was sensed by the Cylinder Head Temperature (CHT) sensor.
- DTC P1285 (Cylinder Head Overtemperature Condition)- Indicates an engine overheat condition was sensed by the CHT (Cylinder Head Temperature) sensor.
- DTC P1299 (Cylinder Head Overtemperature Protection Active)- Indicates an engine overheat condition was detected by the CHT (Cylinder Head Temperature) 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
- Pressure relief cap installation
- Restricted airflow through the A/C condenser/radiator
- Internal engine coolant leak
- Coolant condition/concentration
- Accessory drive components
- Non-OEM engine enhancement components
- Electric cooling fan
- Engine Coolant Temperature (ECT) gauge
- Cylinder Head Temperature (CHT) sensor
- Heater core
- Coolant pump
- Coolant flow restriction
- Missing engine vent hose check valve or incorrect orientation of check valve (3.5L only)
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.
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.
B2 CHECK FOR DTCs
- Check for DTC 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 ECT (Engine Coolant Temperature) gauge operation. REFER to Instrument Panel, Gauges and Warning Indicators. If any other PCM DTCs are retrieved, REFER to Computers and Control Systems for 2.5L engines, Computers and Control Systems for 3.0L (4V) engines or Computers and Control Systems for 3.5L engines.
B3 CHECK FOR AN AIRFLOW OBSTRUCTION
- Check the radiator or A/C condenser for an external obstruction such as leaves or cardboard.
Is an obstruction present?
Yes
REMOVE the obstruction. TEST the system for normal operation.
No
GO to B4.
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.
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 externally?
Yes
REPAIR or INSTALL new components. TEST the system for normal operation.
No
GO to B6.
B6 CHECK THE ENGINE COOLANT FOR AN INTERNAL LEAK
- Inspect the engine coolant in the degas bottle for signs of engine oil.
Is engine oil evident in the coolant?
Yes
If engine oil is evident, Go to Engine for engine diagnosis.
No
GO to B7.
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. If coolant is in the transmission fluid, INSTALL a new radiator. REPAIR the transmission as necessary.
No
GO to B8.
B8 CHECK THE COOLING SYSTEM FOR COMBUSTION GASES
- NOTE: Use UView(R) Combustion Leak Tester, part No. 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 for engine diagnosis.
No
GO to B9.
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 . TEST the system for normal operation.
B10 CHECK THE ELECTRIC COOLING FAN OPERATION
- Start the engine.
- Place the climate control function selector in the MAX A/C position and the blower motor switch in the HI position.
Did the electric cooling fan operate?
Yes
GO to B11.
No
DIAGNOSE the electric cooling fan operation. REFER to Computers and Control Systems Information.
B11 CHECK THE COOLANT PUMP OPERATION
- Start the engine.
- Allow the engine to run for 30 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.
B12 CHECK THE THERMOSTAT OPERATION
- Start the engine.
- Allow the engine to run for 30 minutes. Feel the lower radiator hose.
Is the lower radiator hose hot?
Yes
CHECK the ECT (Engine Coolant Temperature) gauge operation. REFER to Instrument Panel, Gauges and Warning Indicators.
No
For 3.5L engines, GO to B13. For 2.5L and 3.0L engines, GO to B14.
B13 CHECK THE ENGINE VENT HOSE CHECK VALVE
- Disconnect the engine vent hose from the engine and degas bottle.
- Using a light, look inside the end of the vent hose that connects to the engine. A check valve should be installed 50 mm (1.96 in) from the end of the hose.
- Using regulated compressed air, confirm air flows freely from the engine end to the degas bottle end.
- Using regulated compressed air, confirm air does not flow from the degas bottle end to the engine end.
Is the check valve installed in the vent hose and does air flow through in one direction and not the other?
Yes
GO to B14.
No
INSTALL a new engine vent hose. TEST the system for normal operation.
B14 VISUALLY INSPECT THE THERMOSTAT
- Carry out the Thermostat Visual Inspection in the Component Tests. 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.