Circuit Description
This diagnostic monitors the time passed before Closed Loop fuel control occurs. The engine operates in Open Loop when first started. In Open Loop, the powertrain control module (PCM) ignores the oxygen sensor signal and calculates the air/fuel ratio based on inputs from the engine coolant temperature (ECT) sensor, the accelerator pedal position (APP) sensor, and the manifold absolute pressure (MAP) sensor. The PCM will begin Closed Loop fuel control when the oxygen sensor signal is active enough and the ECT sensor reaches a predetermined coolant temperature. If the PCM does not detect Closed Loop fuel control within a predetermined amount of time, this DTC sets.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P0125 Engine Coolant Temperature (ECT) Excessive Time to Closed Loop Fuel Control
Conditions for Running the DTC
| • | DTCs P0030, P0050, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0135, P0155, P0171, P0172, P0174, P0175, P0300-P0306, P0335, P0401, P0404, P0443, P0496, P0506, P0507, P1128, P1129, P2227, P2228, P2229, P2413, P2414, and P2415 are not set. |
| • | The intake air temperature (IAT) sensor 2 is between -7 and +35°C (+20 and +95°F) at start-up. |
| • | The engine coolant temperature is between -7 and 38°C (+20 and +100°F) at engine start up. |
| • | Fuel Cut-Off is not active. |
| • | DTC P0125 runs once per drive cycle when the above conditions are met. |
Conditions for Setting the DTC
The engine coolant temperature does vary more than 2°C (3.6°F) within 20 minutes from engine start.
Action Taken When the DTC Sets
| • | The PCM illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails. |
| • | The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the conditions to the Freeze Frame and updates the Failure Records. |
Conditions for Clearing the MIL/DTC
| • | The PCM turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail. |
| • | A last test failed, or current DTC, clears when the diagnostic runs and does not fail. |
| • | A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic. |
| • | Use a scan tool in order to clear the MIL and the DTC. |
Diagnostic Aids
| • | Check for any of the following conditions: |
| - | A DTC P0125 can indicate a skewed ECT sensor. Comparing the coolant temperature displayed on a scan tool with the actual engine coolant temperature measured with a thermometer may isolate the fault. If the displayed engine coolant temperature is not close to the actual engine coolant temperature, replace the ECT sensor. Refer to Temperature Versus Resistance - Engine Coolant Temperature Sensor . |
| - | Check for the proper operation of the thermostat. Refer to Thermostat Diagnosis in Engine Cooling. |
| • | An intermittent malfunction may be caused by a fault in the ECT sensor electrical circuit. Inspect the wiring harness and the components for an intermittent condition. Refer to Intermittent Conditions . |
| • | If the DTC P0125 cannot be duplicated, the information included in the Freeze Frame data can be useful in determining vehicle operating conditions when the DTC was first set. |
Test Description
The numbers below refer to the step numbers in the diagnostic table.
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The Diagnostic System Check - Vehicle prompts the technician to complete some basic checks and store the Freeze Frame data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.
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This step determines if there is a cooling system malfunction.
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This step compares the ECT to the intake air temperature (IAT). This inspection is to be performed when the vehicle has reached the ambient room temperature. At that time both the surrounding air temperature and the engine coolant temperature are nearly equal. If the ECT sensor and circuit are OK, both sensors should indicate the same temperature.
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The fault not present indicates the condition that caused DTC P0125 to set is intermittent and not currently present. If no other DTCs are stored, refer to Diagnostic Aids for additional information on diagnosing an intermittent DTC P0125.
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After replacing the PCM, the relationship between the crankshaft position (CKP) sensor and the crankshaft must re-established. A new minimum throttle position and idle speed must also be established.
Step | Action | Value(s) | Yes | No | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics Connector End View Reference: Powertrain Control Module Connector End Views or Engine Controls Connector End Views | ||||||||||||
Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | Go to Diagnostic System Check - Vehicle in Vehicle DTC Information | |||||||||
Review the list below for any of the following customer concerns:
Did you identify a customer concern from the list above? | -- | Go to Step 8 | Go to Step 3 | |||||||||
Are the ECT and the IAT readings within 2 or 3 degrees of each other? | -- | Go to Step 4 | Go to Step 6 | |||||||||
4 |
Does the ECT increase by more than the specified value within the 10 minutes? | 20°C (68°F) | Go to Step 5 | Go to Step 8 | ||||||||
The fault is not present. Are there any DTCs stored that have not been diagnosed? | -- | Go to Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information | Go to Diagnostic Aids | |||||||||
6 |
Is the resistance of the ECT sensor within specifications? | -- | Go to Step 7 | Go to Step 9 | ||||||||
7 |
Did you find and correct the condition? | -- | Go to Step 11 | Go to Step 10 | ||||||||
8 |
Did you complete the action? | -- | Go to Step 11 | -- | ||||||||
9 | Replace the ECT sensor. Refer to Engine Coolant Temperature Sensor Replacement . Did you complete the replacement? | -- | Go to Step 11 | Go to Step 10 | ||||||||
Did you complete the replacement? | -- | Go to Step 11 | -- | |||||||||
11 |
Does the DTC run and pass? | -- | Go to Step 12 | Go to Step 2 | ||||||||
12 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | Go to Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information | System OK | ||||||||
