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. From the coolant pump, coolant is sent through the engine block and cylinder heads. A separate circuit from the engine also feeds the heater core with coolant. On most engines, the coolant pump is operated by engine rotation through a pulley which is driven by the accessory drive belt to circulate the coolant. Some engines use a belt driven by a pulley attached to the camshaft, and some engines use a sprocket driven by the timing chain to operate the coolant pump. 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 is allowed to flow 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 vehicle/engine specific information, refer to Engine Cooling .

• DTC P0217 Engine Coolant Overtemperature Condition
• DTC P1285 Cylinder Head Overtemperature Condition
• DTC P1299 Cylinder Head Overtemperature Protection Active

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 (if equipped)
• Mechanical cooling fan blade (if equipped)
• Mechanical cooling fan clutch (if equipped)
• Engine coolant temperature (ECT) indicator system (gauge)
• ECT sensor (if equipped)
• Cylinder head temperature (CHT) sensor (if equipped)
• Heater core
• Coolant pump
• Coolant flow restriction

PINPOINT TEST B: THE ENGINE OVERHEATS 

1. B1 CARRY OUT INSPECTION AND VERIFICATION 
   • Carry out the Inspection & Verification .
   • Were any concerns found? 
   1. YES  : REPAIR as needed. TEST the system for normal operation.
   2. NO  : Go to  B2.
2. B2 CHECK FOR DTCs 
   NOTE: Refer to the Introduction - Gasoline Engines article for correct scan tool hook-up procedure.
   • Check for DTC P0217, P1285 or P1299.
   • Is DTC P0217, P1285 or P1299 present? 
   1. YES  : Go to  B3.
   2. NO  : Actual engine overheating has not been verified. CHECK the ECT gauge operation. REFER to INSTRUMENTATION, MESSAGE CENTER, & WARNING CHIMES article. If any other DTCs are retrieved, REFER to the Introduction - Gasoline Engines article.
3. 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? 
   1. YES  : REMOVE the obstruction. TEST the system for normal operation.
   2. NO  : Go to  B4.
4. B4 CHECK THE ENGINE COOLANT LEVEL 
   NOTE: Allow the engine to cool before checking the coolant level.
   • Key in OFF position.
   • Visually check the engine coolant level in the degas bottle or coolant expansion tank.
   • Is the engine coolant level within specification? 
   1. YES  : Go to  B5.
   2. NO  : ADJUST the engine coolant level as necessary. Go to  B5.
5. B5 PRESSURE TEST THE ENGINE COOLING SYSTEM 
   • Pressure test the engine cooling system. Refer to Component Tests .
   • Does the engine cooling system leak? 
   1. YES  : REPAIR or INSTALL new components. TEST the system for normal operation.
   2. NO  : Vehicles equipped with an expansion tank, go to  B6. Vehicles equipped with a degas bottle, go to  B7.
6. B6 CHECK THE PRESSURE RELIEF CAP 
   • Carry out the pressure relief cap pressure test. Refer to Component Tests .
   • Is the pressure relief cap OK? 
   1. YES  : Go to  B7.
   2. NO  : INSTALL a new pressure relief cap. TEST the system for normal operation.
7. B7 CHECK THE ENGINE COOLANT FOR AN INTERNAL LEAK 
   • Inspect the engine coolant in the degas bottle or coolant expansion tank for signs of engine oil or transmission fluid.
   • Is engine oil or transmission fluid evident in the coolant? 
   1. YES  : If engine oil is evident, go to ENGINE SYSTEM - GENERAL INFORMATION article for engine diagnosis. If transmission fluid is evident, INSTALL a new radiator. REPAIR the transmission as necessary. Refer to the appropriate Automatic Transmission article for the procedure. TEST the system for normal operation.
   2. NO  : Go to  B8.
8. B8 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? 
   1. YES  : If coolant is in the engine oil, go to ENGINE SYSTEM - GENERAL INFORMATION article. If coolant is in the transmission fluid, INSTALL a new radiator. REPAIR the transmission as necessary. Refer to the appropriate Automatic Transmission article for the procedure.
   2. NO  : Go to  B9.
9. B9 CHECK THE COOLING SYSTEM FOR COMBUSTION GASES 
   NOTE: Use U-View® Combustion Leak Tester part number 560000 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? 
   1. YES  : Go to ENGINE SYSTEM - GENERAL INFORMATION article for engine diagnosis.
   2. NO  : Go to  B10.
10. B10 CHECK COOLANT CONDITION 
    • Check the coolant for dirt, rust or contamination and check the coolant concentration.
    • Is the coolant condition OK? 
    1. YES  : Vehicles equipped with an electric cooling fan, go to  B11. Vehicles equipped with only a mechanical cooling fan, go to  B12.
    2. NO  : FLUSH the engine cooling system. REFER to Cooling System Flushing . TEST the system for normal operation.
11. B11 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? 
    1. YES  : If the vehicle is also equipped with a mechanical cooling fan, go to  B12. Otherwise, go to  B13.
    2. NO  : DIAGNOSE the electric cooling fan operation. REFER to Introduction - Gasoline Engines article.
12. B12 CHECK THE MECHANICAL COOLING FAN OPERATION 
    • Key in OFF position.
    • If the vehicle is equipped with a viscous fan clutch, carry out the Fan Clutch Tests in Component Tests . If the vehicle is equipped with an electronically actuated fan clutch, refer to the Introduction - Gasoline Engines article.
    • Is the cooling fan operation OK? 
    1. YES  : Go to  B13.
    2. NO  : INSTALL a new fan clutch. TEST the system for normal operation.
13. B13 CHECK THE COOLANT PUMP OPERATION 
    • Start the engine.
    • Allow the engine to run for 10 minutes (hot side thermostat equipped vehicles) or 30 minutes (cold side thermostat equipped vehicles). Place the climate control function selector in the MAX HEAT position. Feel the heater outlet hose.
    • Is the heater outlet hose hot? 
    1. YES  : Go to  B14.
    2. NO  : INSTALL a new coolant pump. TEST the system for normal operation.
14. B14 CHECK THE THERMOSTAT OPERATION 
    • Start the engine.
    • Allow the engine to run for 10 minutes (hot side thermostat equipped vehicles) or 30 minutes (cold side thermostat equipped vehicles). Feel the upper radiator hose (hot side thermostat equipped vehicles) or the lower radiator hose (cold side thermostat equipped vehicles).
    • Is the upper (hot side thermostat equipped vehicles) or lower (cold side equipped vehicles) radiator hose hot? 
    1. YES  : CHECK the engine coolant temperature gauge operation. REFER to INSTRUMENTATION, MESSAGE CENTER, & WARNING CHIMES article.
    2. NO  : Go to  B15.
15. B15 VISUALLY INSPECT THE THERMOSTAT 
    • Carry out the Thermostat Visual Inspection in the Component Tests .
    • Is the thermostat damaged? 
    1. YES  : INSTALL a new thermostat. TEST the system for normal operation.
    2. 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.