P0125
P0125-INSUFFICIENT COOLANT TEMP FOR CLOSED-LOOP FUEL CONTROL
For a complete wiring diagram, refer to the Wiring Information Electrical Diagrams.
Theory of Operation
The engine coolant temperature sensor is a negative temperature coefficient thermistor-type sensor. The resistance varies inversely with temperature. At cold temperatures the sensor resistance is and voltage is high. As the coolant temperature increases, the resistance decreases and the voltage becomes low. The insufficient coolant temp for closed-loop fuel control determines if the engine coolant temperature reaches the closed loop fueling control temperature limit in a regulated time after start.
- When Monitored:
With the battery voltage greater than 10.4 Volts and after engine is started.
- Set Condition:
The engine temperature does not go greater than -10° C (15° F). Failure time depends on start-up coolant temperature and ambient temperature, (2) two minutes for a start temp of -10° C (15° F) or up to 10 minutes for a vehicle with a start-up temp of -28° C (5° F). Two Trip Fault. Three good trips to turn off the Malfunction Indicator Lamp (MIL).
WARNING: On vehicles equipped with the high voltage system, you must thoroughly read and follow all High Voltage Safety procedures. In addition, before performing any diagnostic or service procedure near a high voltage component, you must perform the High Voltage Power Down. Failure to follow these instructions may result in possible serious or fatal injury
Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. Pre-Diagnostic Troubleshooting Procedure.
1. CHECKING COOLANT LEVEL AND CONDITION
NOTE: If a Engine Coolant Temperature (ECT) DTC is set along with this code, diagnose the ECT DTC first.
NOTE: Inspect the ECT terminals and related PCM terminals. Make sure the terminals are free from corrosion and damage.
NOTE: The most effective way to diagnose this DTC is to allow the vehicle to sit overnight outside, in order to have a completely cold soaked engine.
NOTE: Extremely cold outside ambient temperatures may cause this DTC to set.
WARNING: Never open the cooling system when the engine is hot. The system is under pressure. Extreme burns or scalding may result. Failure to follow these instructions can result in possible serious or fatal injury. Allow the engine to cool before opening the cooling system.
1. Inspect the coolant system for proper level and condition.
Is the coolant level and condition OK?
Yes
- Go To 2
No
- Inspect the vehicle for a coolant leak, make the appropriate repairs and add the correct amount of coolant.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.
2. THERMOSTAT OPERATION
NOTE: This test works best if performed on a cold engine (cold soak)
1. Ignition on, engine not running.
2. With the scan tool, read the Eng Coolant Tmp Deg value. If the engine was allowed to sit overnight (cold soak), the temperature value should be a sensible value that is somewhere close to the ambient temperature.
NOTE: If engine coolant temperature is greater than 82° C (180° F), allow the engine to cool until 65° C (150° F) is reached.
3. Start the engine.
4. During engine warm-up monitor the Eng Coolant Tmp Deg value. The temp deg value change should be a smooth transition from start up to the normal operating temp of 82° C (180° F). Also monitor the actual coolant temperature with a thermometer.
NOTE: As the engine warms up to the operating temperature, the actual coolant temperature (thermometer reading) and the scan tool Eng Coolant Tmp Deg values should stay relatively close to each other.
5. Using the appropriate service information, determine the proper opening temperature of the thermostat.
Did the thermostat open at the proper temperature?
Yes
- Go To 3
No
- Replace the thermostat.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.
3. ECT SENSOR OPERATION
1. Ignition on, engine not running.
2. With the scan tool, read the Eng Coolant Tmp Deg value. If the engine was allowed to sit overnight (cold soak), the temperature value should be a sensible value that is somewhere close to the ambient temperature.
NOTE: If engine coolant temperature is greater than 82° C (180° F), allow the engine to cool until 65° C (150° F) is reached.
3. Start the Engine.
4. During engine warm-up monitor the Eng Coolant Tmp Deg value. The temp deg value change should be a smooth transition from start up to the normal operating temp 82° C (180° F). Also monitor the actual coolant temperature with a thermometer.
NOTE: As the engine warms up to operating temperature, the actual coolant temperature (thermometer reading) and the scan tools Eng Coolant Tmp Deg value should stay relatively close to each other.
Is the thermometer reading relatively close to the scan tool ECT reading?
Yes
- The conditions that set this DTC are no longer present.
- Refer to the INTERMITTENT CONDITION Diagnostic Procedure for further assistance. Intermittent Condition Test
No
- Replace the ECT sensor.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.