Pinpoint Test C: The Engine Does Not Reach Normal Operating Temperature
Engine Cooling
Pinpoint Tests
Pinpoint Test C: The Engine Does Not Reach Normal Operating Temperature
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. 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 is allowed to flow through the radiator circuit in order to transfer engine generated heat to the outside air.
Concerns of engine inability to reach normal operating temperature typically occur when the rate of coolant flow through some coolant circuits (radiator, heater core) is more than expected given the conditions or the fan clutch is always engaged. Heat is not allowed to build in the engine because a heat exchanger is removing too much heat, including the radiator, heater core and oil cooler. In addition, perceived concerns that the engine does not reach normal operating temperature can be related to a low coolant level or trapped air which does not allow for hot coolant to be available at the heater core, an inoperative climate control system, or for concerns perceived or related to an incorrect engine temperature gauge indication.
For engine specific information, refer to Engine Cooling Description and Operation in the Description and Operation.
- DTC P0125 (Insufficient Coolant Temp for Closed Loop Fuel Control) - Indicates the Engine Coolant Temperature (ECT) sensor (4.0L SOHC) or the Cylinder Head Temperature (CHT) sensor (4.6L [3V]) has not achieved the required temperature level to enter closed loop operating conditions within a specified amount of time after starting the engine.
- DTC P0128 (Coolant Thermostat (Coolant Temp Below Thermostat Regulating Temperature)) - Indicates the thermostat monitor has not achieved the required engine operating temperature within a specified amount of time after starting the engine.
This pinpoint test is intended to diagnose the following:
- Low coolant level
- Thermostat
- Engine Coolant Temperature (ECT) indicator system (gauge)
- Engine cooling fan
PINPOINT TEST C: THE ENGINE DOES NOT REACH NORMAL OPERATING TEMPERATURE
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.
-------------------------------------------------
C1 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 C2.
-------------------------------------------------
C2 CHECK FOR DTC P0125 or P0128
NOTE: Refer to Inspection and Verification for correct scan tool hook-up procedure. Inspection and Verification
- Check for DTC P0125 or P0128.
- Is DTC P0125 or P0128 present?
Yes
GO to C3.
No
The cooling system is operational. If an inoperative engine coolant temperature gauge is suspected, CHECK the engine coolant temperature gauge operation. REFER to Instrument Panel, Gauges and Warning Indicators.
If an inoperative climate control system is suspected, CHECK the climate control system operation. REFER to Heating and Air Conditioning. If any other DTCs are retrieved, REFER to Computers and Control Systems Information.
-------------------------------------------------
C3 CHECK THE COOLING FAN OPERATION
- Check the cooling fan clutch operation. Refer to Computers and Control Systems Information.
- Is the cooling fan clutch OK?
Yes
GO to C4.
No
INSTALL a new cooling fan clutch. TEST the system for normal operation.
-------------------------------------------------
C4 CHECK THE COOLANT LEVEL
- NOTE: Allow the engine to cool before checking the coolant level.
- Visually check the engine coolant level in the coolant expansion tank.
- Is the engine coolant level within specification?
Yes
INSTALL a new thermostat. TEST the system for normal operation.
No
GO to Pinpoint Test A to diagnose a coolant leak. Pinpoint Test A: Loss Of Coolant
-------------------------------------------------