Pinpoint Test C : The Engine Does Not Reach Normal Operating Temperature
- Normal Operation and Fault Conditions
The engine cooling system maintains engine temperature 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 circulates 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 to transfer engine-generated heat to the outside air. This engine also incorporates an additional cylinder block thermostat to control a mini coolant circuit. When the cylinder block thermostat closed coolant only flows through the exhaust side of the cylinder head. From here the coolant arrives at the oil cooler via the heater core and from there it is passed to the coolant pump. In this phase there is no coolant flow in the cylinder block nor on the intake side of the cylinder head. This leads to rapid warm-up of the engine and the engine oil, through which the friction at the lubrication points is reduced at an early stage. When the cylinder block thermostat opens coolant flows through the cylinder block and intake side of the cylinder head similar to a conventional cooling system.
Concerns of engine inability to reach normal operating temperature typically occur when the rate of coolant flow through some coolant circuits (cylinder block, radiator) is more or less than expected given the conditions. Heat is not allowed to build in the engine because a heat exchanger is removing too much heat, including the radiator. 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.
DTC Fault Trigger Conditions
DTC Description Fault Trigger Condition PCM P0125:00 Insufficient Coolant Temp For Closed Loop Fuel Control: No Sub Type Information Indicates the CHT sensor or ECT sensor has not achieved the required temperature level within specified amount of time after starting the engine. PCM P0128:00 Coolant Thermostat (Coolant Temp Below Thermostat Regulating Temperature): No Sub Type Information Indicates that the thermostat monitor has not achieved the required engine operating temperature within a specified amount of time after starting the engine. Possible Sources
- Low coolant level
- Thermostat
- Cylinder block thermostat
- Temperature gauge
- Trapped air
- WARNING: 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 in this article.
Were any concerns found?
Yes REPAIR as needed. No GO to C2 - C2 CHECK FOR DTC P0125 OR P0128
- Using a scan tool, perform PCM self-test.
Is DTC P0125 or P0128 present?
Yes GO to C3 No The cooling system is operational. If an inoperative temperature gauge is suspected, CHECK the temperature gauge operation. REFER to: Instrumentation, Message Center and Warning Chimes . If an inoperative climate control system is suspected, CHECK the climate control system operation. If any other DTCs are retrieved, REFER to: Electronic Engine Controls . - C3 CHECK THE COOLANT LEVELNOTE: Allow the engine to cool before checking the coolant expansion tank.
- Visually check the engine coolant level in the coolant expansion tank
Is the engine coolant level within specification?
Yes GO to C4 No GO to Pinpoint Test A - C4 CHECK THE ECT (ENGINE COOLANT TEMPERATURE) SENSOR OPERATION
- Using a scan tool, view PCM PIDs.
- Monitor the ECT temperature PID.
- Using an Infrared temperature gun measure and record the temperature of the coolant outlet housing at the rear of the cylinder head near the ECT sensor.
Is the temperature reading similar to the ECT PID value?
Yes INSTALL a new thermostat housing. REFER to: Thermostat Housing . Using a scan tool clear the DTC. Test the vehicle for normal operation. If the DTC repeats INSTALL a new cylinder block thermostat. REFER to: Cylinder Block Thermostat . No INSTALL a new ECT sensor. REFER to: Engine Coolant Temperature (ECT) Sensor .