Circuit Description
The engine coolant temperature (ECT) sensor monitors the temperature of the coolant. This input is used by the powertrain control module (PCM) for engine control and as an enabling criterion for some diagnostics.
The air flow coming into the engine is accumulated and used to determine if the vehicle has been driven within conditions that would allow the engine coolant to heat up normally to the Closed Loop temperature. If the ECT does not increase normally or does not reach regulating temperature of the thermostat, diagnostics that use the ECT as an enabling criterion may not run when expected.
This diagnostic trouble code (DTC) will only run once per ignition cycle within the enabling conditions.
If the PCM detects that more than a calibrated amount of time has been met to reach a minimum coolant temperature required for Closed Loop fuel control, DTC P0125 sets.
Conditions for Running the DTC
| • | DTCs P0110, P0111, P0112, P0113, P0116, P0117, P0118, P1114, P1115 are not set. |
| • | The minimum intake air temperature (IAT) is more than -7°C (19°F). |
| • | The ECT at start up is less than 50°C (122°F). |
| • | The ECT at start up is more than -40°C (-40°F). |
Conditions for Setting the DTC
An excessive amount of time passes before the ECT reaches the Closed Loop operation 10°C (50°F) threshold. The amount of time ranges between 2-13 minutes, depending on the ECT at start up and the amount of air cycled through the engine since start up.
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. |
Diagnostic Aids
| • | A DTC P0125 is designed to detect a skewed ECT sensor or a faulty thermostat. |
| • | A skewed IAT sensor may cause this DTC to set. The IAT sensor should read near the ambient temperature while driving. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
This step tests for excess resistance in the ECT circuit.
-
This step tests for a skewed sensor through the range of temperatures affecting this DTC.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics Connector End View Reference: Powertrain Control Module Connector End Views or Engine Controls Connector End Views | ||||
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | |
2 | Is the cooling system coolant low? | -- | Go to Loss of Coolant in Engine Cooling | Go to Step 3 |
Is the ECT sensor parameter more than the specified value? | 138°C (280°F) | Go to Step 7 | Go to Step 4 | |
Is the ECT sensor parameter more than the specified value? | 138°C (280°F) | Go to Step 5 | Go to Step 6 | |
5 | Test the low reference circuit for a high resistance and for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 10 | -- |
6 | Test the ECT sensor signal circuit for a high resistance and for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 10 | -- |
7 |
Do the resistance and the temperature closely match the Temperature vs Resistance table? | 10-90°C (50-94°F) | Go to Step 8 | Go to Step 9 |
8 | Install the ECT sensor. Refer to Engine Coolant Temperature Sensor Replacement . Is the action complete? | -- | Go to Thermostat Diagnosis in Engine Cooling | -- |
9 | Replace the ECT sensor. Refer to Engine Coolant Temperature Sensor Replacement . Did you complete the replacement? | -- | Go to Step 10 | -- |
10 |
Did the DTC fail this ignition? | -- | Go to Diagnostic Aids | Go to Step 11 |
11 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | System OK | |
