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P0125



DTC P0125

DTC DESCRIPTOR

DTC P0116
Engine Coolant Temperature (ECT) Sensor Performance

DTC P0125
Engine Coolant Temperature (ECT) Insufficient for Closed Loop Fuel Control

DTC P0128
Engine Coolant Temperature (ECT) Below Thermostat Regulations Temperature

DIAGNOSTIC FAULT INFORMATION

IMPORTANT: Always perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Testing and Inspection






TYPICAL SCAN TOOL DATA

ECT Sensor Temperature:






CIRCUIT/SYSTEM DESCRIPTION

P0116
The engine coolant temperature (ECT) sensor is a variable resistor that measures the temperature of the engine coolant. The control module supplies 5 volts to the signal circuit and a ground for the ECT low reference circuit. When the engine coolant temperature is low, the sensor resistance is high. When the engine coolant temperature is high, the sensor resistance is low. The control module uses this High Side Coolant Rationality test to determine if the ECT input is skewed high. The internal clock of the control module will record the amount of time the ignition is OFF. At restart the control module will compare the temperature difference between the ECT and the intake air temperature (IAT). Before failing this test, the control module will perform a calculation to determine the presence of an engine block heater. If the control module detects that the temperature difference between the ECT and the IAT is not within the calibrated range after the ignition OFF time, DTC P0116 sets.

P0125
An ECT sensor monitors the temperature of the coolant. This input is used by the control module for engine control and as an enabling criteria for some diagnostics. The air flow into the engine is accumulated and used to determine if the vehicle has been driven within the conditions that would allow the engine coolant to heat up normally to the Closed Loop temperature. If the coolant temperature does not increase normally or does not reach the Closed Loop temperature, the diagnostics that use engine coolant temperature as enabling criteria may not run when expected. If the control module detects the calibrated amount of air flow and engine run time have been met, and the engine coolant has not met the Closed Loop temperature, DTC P0125 sets.

P0128
An ECT sensor monitors the temperature of the coolant. This input is used by the control module for engine control and as an enabling criteria for some diagnostics. The air flow coming into the engine is accumulated and used to determine if the vehicle has been driven within the conditions that would allow the engine coolant to heat up normally to the thermostat regulating temperature. If the coolant temperature does not increase normally or does not reach the regulating temperature of the thermostat, the diagnostics that use ECT as enabling criteria may not run when expected. If the control module detects the calibrated amount of air flow and engine run time have been met, and the ECT has not met the minimum thermostat regulating temperature, DTC P0128 sets.

CONDITIONS FOR RUNNING THE DTC

P0116
- DTCs P0112, P0113, P0117, P0118, P0502, P0503, P0601, P0602, P0604, P0606, P2610 are not set.
- The ignition is ON.
- The IAT Sensor parameter is more than 15°C (59°F).
- The Fuel Level Sensor parameter is more than 10 percent.
- The vehicle has a minimum ignition OFF time of 8 hours.
- This diagnostic runs once per ignition cycle when the above conditions are met.

P0125
- DTCs P0101, P0102, P0103, P0112, P0113, P0117, P0118, P0502, or P0503 are not set.
- The minimum air temperature is more than -7°C (+19°F).
- The start-up ECT is less than 10°C (50°F)
- The engine run time is between 30-1,800 seconds.
- The vehicle has traveled more than 0.8 kilometer (0.5 mile) at more than 8 km/h (5 mph).
- This diagnostic runs once per ignition cycle when the above conditions are met.

P0128
- DTCs P0101, P0102, P0103, P0112, P0113, P0117, P0118, P0502, or P0503 are not present.
- The startup ECT is less than 75°C (167°F).
- The intake air temperature (IAT) is more than -7°C (+19°F).
- The engine run time is between 30-1,800 seconds.
- The vehicle is driven more than 0.8 kilometer (0.5 mile) at more than 8 km/h (5 mph).
- This diagnostic runs once per ignition cycle when the above conditions are met.

CONDITIONS FOR SETTING THE DTC

P0116
- The control module detects a temperature difference between the ECT sensor and the IAT sensor of more than 100°C (180°F) at start up. OR
- The control module detects a temperature difference between the ECT sensor and the IAT sensor of more than 15°C (27°F) and the time elapsed cranking the engine without starting is more than 5 seconds. OR
- The control module detects a temperature difference between the ECT sensor and the IAT sensor of more than 15°C (27°F). The vehicle must then be driven for 5 minutes over 40 km/h (25 mph). If the IAT sensor temperature decreases more than 5°C (9°F), an engine block heater was detected and the test is aborted. If the IAT sensor temperature does not decrease, an engine block heater was not detected and DTC P0116 will set.

P0125
The control module detects that the actual amount of accumulated airflow is more than the predicted amount of accumulated air flow before the ECT reaches 15°C (59°F).

P0128
The control module detects that the actual amount of accumulated air flow is more than the predicted amount of accumulated air flow before the ECT reaches 80°C (176°F).

ACTION TAKEN WHEN THE DTC SETS
- The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
- The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

CONDITIONS FOR CLEARING THE MIL/DTC
- The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
- A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
- A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
- Clear the MIL and the DTC with a scan tool.

CIRCUIT/SYSTEM TESTING

P0116
1. Inspect the cooling system coolant level, if low then refer to Loss of Coolant. Loss of Coolant

IMPORTANT: The cooling fans are commanded ON when certain ECT DTCs are set.

2. Observe and record the ambient air temperature of the vehicle environment using an accurate thermometer.
3. After the vehicle has been OFF for 8 hours, remove the mass air flow (MAF)/IAT sensor.

IMPORTANT: The vehicle needs to have been OFF for at least 8 hours for the ECT and the IAT to be at ambient temperature. The vehicle should not have changed environments during this time.

4. Remove the ECT sensor.
5. Place the sensors on a work surface away from any heat source. Allow the sensors to reach the ambient air temperature for 30-60 minutes.
6. Connect the MAF/IAT sensor and the ECT sensor to the electrical connector, but DO NOT install them. Insulate the sensors from any engine heat source.
7. Turn ON the ignition and take a snapshot of the Engine Data List with a scan tool. Refer to Scan Tool Snapshot Procedure. Component Tests and General Diagnostics

IMPORTANT: The IAT sensor will start to warm-up as soon as the ignition is turned ON.

8. Review the snapshot data that was taken with the scan tool. Observe the ECT Sensor and IAT Sensor parameters with a scan tool. Is the difference between the ECT Sensor parameter and the IAT Sensor parameter more than 15°C (27°F)?
- If less than 15°C (27°F), then refer to Testing for Intermittent Conditions and Poor Connections. Component Tests and General Diagnostics

9. Observe the recorded IAT Sensor and ECT sensor parameters. Is the difference between the IAT Sensor, ECT Sensor parameters, and the ambient air temperature less than 8°C (14°F).
- If less than 8°C (14°F), refer to Testing for Intermittent Conditions and Poor Connections. Component Tests and General Diagnostics
10. Disconnect the MAF/IAT sensor. Test for an intermittent and for a poor connection at the IAT sensor.
11. At the sensor, measure the resistance between the IAT signal and the IAT low reference terminals with a DMM and record the value. Observe the recorded ambient air temperature. Compare the resistance measurement of the IAT sensor to the ambient air temperature using the Temperature vs Resistance.
- If not within specified range, then replace the MAF/IAT sensor.
12. Disconnect the ECT sensor, and inspect for the ECT sensor leaking engine coolant internally through the sensor, corrosion on the ECT sensor terminals, or for corrosion on the ECT harness connector terminals.
13. At the sensor, measure the resistance between the ECT signal and the ECT low reference terminals with a DMM and record the value. Observe the recorded ambient air temperature. Compare the resistance measurement of the ECT sensor to the ambient air temperature using the Temperature vs Resistance.
- If not within specified range, then replace the ECT sensor.

IMPORTANT: DO NOT hold the ECT sensor by the probe.

14. Measure for 4.8-5.2 volt from the IAT signal circuit to a good ground with a DMM.
- If not within specified range, then test the IAT signal circuit for a high resistance, or for an intermittent and for a poor connection at the control module. If circuits test OK then replace the control module.
15. Turn OFF the ignition for 90 seconds to allow the control modules to power down.
16. Measure for 4.8-5.2 volt from the ECT signal circuit to a good ground with a DMM.
- If within the specified range, then go to intermittent conditions. Component Tests and General Diagnostics
- If NOT within specified range, then test the ECT signal circuit for a high resistance or short to ground or for shorted terminals and poor connections at the control module. If circuits test OK then replace the control module.
17. Measure for 5 ohms of resistance from the low reference circuit of the IAT sensor to a good ground with a DMM.
- If less than 5 ohms, then go to Diagnostic Aids for Circuit Testing and Wiring Repair Procedures. Component Tests and General Diagnostics
- If more then 5 ohms, then test the IAT low reference circuit for high resistance or for an intermittent and for a poor connection at the control module. If circuits test OK then replace the control module.

IMPORTANT:
- All electrical components and accessories must be turned OFF.
- Performing this step will disable the diagnostic for 8 hours.

P0125 or P0128
1. Inspect the cooling system coolant level, if low then refer to Loss of Coolant. Loss of Coolant

IMPORTANT: The cooling fans are commanded ON when certain ECT DTCs are set.

2. Inspect for the following conditions:
- Corrosion on the ECT terminals
- Improper or corroded terminals at the ECT harness connector
- Loose terminals in the ECT harness connector.
3. Measure for 4.8-5.2 volts from the signal circuit of the ECT sensor to a good ground with a DMM.
- If not within specified range, test the ECT sensor signal circuit for high resistance, or for an intermittent and for a poor connection at the control module. If circuits test OK then replace the control module.
4. Measure for 4.8-5.2 volts from the signal circuit of the ECT sensor to the low reference circuit of the ECT sensor with a DMM.
- If not within specified range, test the ECT sensor low reference circuit for high resistance, or for an intermittent and for a poor connection at the control module.
- If circuits test OK, then replace the control module.
5. Turn OFF the ignition. Remove the ECT sensor. Place the sensor on a work surface away from any heat source.
6. Allow the sensor to reach ambient air temperature for 30-60 minutes.
7. Observe and record the ambient air temperature of the vehicle environment using an accurate thermometer.
8. At the sensor, measure the resistance between the ECT signal and the ECT low reference terminals with a DMM and record the value.

IMPORTANT: DO NOT hold the ECT sensor by the probe.

9. Compare the resistance measurement of the ECT sensor to the ambient air temperature on the Temperature vs Resistance.
- If within specified range, then install the ECT sensor and refer to Testing for Intermittent Conditions and Poor Connections. Component Tests and General Diagnostics
- If NOT within specified range, then replace the ECT sensor.

REPAIR INSTRUCTIONS

IMPORTANT: Always perform the Diagnostic Repair Verification after completing the diagnostic procedure.
- Mass Air Flow (MAF) Sensor Replacement
- Engine Coolant Temperature (ECT) Sensor Replacement
- Control Module References for PCM replacement, setup, and programming. Verification Tests

REPAIR VERIFICATION
Diagnostic Repair Verification
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