Circuit Description
The DTC P0125 Engine Coolant Temperature (ECT) Excessive Time to Closed Loop Fuel Control 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 sensor, the throttle position sensor, and the mass air flow 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. The PCM expects to begin closed loop fuel control within a specified amount of time.
Conditions for Running the DTC
The HO2S 1 output is varying, indicating that the sensor is hot enough to operate properly.
Conditions for Setting the DTC
| • | Engine coolant temperature sufficient to allow closed loop operation (20°C/68°F) is not achieved within a predetermined time frame. |
| • | The diagnostic will run once per drive cycle. |
Action Taken When the DTC Sets
| • | The PCM illuminates the malfunction indicator lamp (MIL) after two consecutive ignition cycles in which the diagnostic runs with the fault active. |
| • | The PCM records the operating conditions at the time the diagnostic fails. This information is stored in the Freeze Frame buffer. |
Conditions for Clearing the MIL/DTC
| • | The MIL turns OFF after three consecutively passing trips without a fault present. |
| • | A History DTC clears after 40 consecutive warm-up cycles without a fault. |
| • | Use the scan tool Clear DTC Information function or disconnect the PCM battery feed in order to clear 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 Engine Coolant Temperature Sensor Replacement . |
| • | Check for the proper operation of the thermostat. Refer to Thermostat Diagnosis in Engine Cooling. |
If the DTC P0125 is intermittent, driving the vehicle under the following conditions can verify whether the fault is present. Perform the scan tool Clear DTC Information function. Road test the vehicle while monitoring the DTC P0125 diagnostic on the scan tool under the Not Ran Since Code Cleared selection in the DTC Information menu. If a DTC P0125 appears in the Not Ran Since Code Cleared list, the P0125 diagnostic has not yet run. When the DTC P0125 does not appear in the Not Ran Since Code Cleared list, the P0125 diagnostic has run. If the MIL is NOT ILLUMINATED and there is no PENDING DTC Status in DTC Information, the P0125 diagnostic has passed. DTCs MUST BE CLEARED in order to view the CURRENT STATUS of the Not Ran Since Code Cleared list. DO NOT FORGET that the Not Ran Since Code Cleared list only indicates that the test has run, not whether the test passed or failed. The DTC Information screen must be checked for CURRENT or PENDING status, in order to determine the outcome of the diagnostic test involved.
An intermittent malfunction may be caused by a fault in the ECT sensor electrical circuit. Inspect the wiring harness and components for an intermittent condition. Refer to Intermittent Conditions .
If you cannot duplicate the DTC P0125, 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-Engine Controls prompts the technician to complete some basic checks and to 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 compares the ECT temperature to the IAT temperature. This inspection is to be performed when the vehicle has reached 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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Fault not present indicates the condition that caused a 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 P0125.
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After performing the scan tool Clear DTC Information function, the DTC P0125 diagnostic can be monitored on the scan tool under the Not Ran Since Code Cleared selection in the DTC Information menu. If a DTC P0125 appears in the Not Ran Since Code Cleared list, the P0125 diagnostic has not yet run. When the DTC P0125 does not appear in the Not Ran Since Code Cleared list, the P0125 diagnostic has run. If the MIL is NOT ILLUMINATED and there is no PENDING DTC Status in DTC Information, the P0125 diagnostic has passed. DTCs MUST BE CLEARED in order to view the CURRENT STATUS of the Not Ran Since Code Cleared list. DO NOT FORGET that the Not Ran Since Code Cleared list only indicates that the test has run, not whether the test passed or failed. The DTC Information screen must be checked for CURRENT or PENDING status, in order to determine the outcome of the diagnostic test involved.
Step | Action | Value(s) | Yes | No | ||||||
|---|---|---|---|---|---|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics | ||||||||||
Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | ||||||||
Are the ECT and the IAT readings within 2 or 3 degrees of each other? | -- | Go to Step 3 | Go to Step 6 | |||||||
3 |
Did the ECT indicated on the scan tool increase by more than the specified value within the 10 minutes? | 20°C (68°F) | Go to Step 5 | Go to Step 4 | ||||||
4 | Are there any ECT sensor DTCs set? | -- | Go to Step 8 | |||||||
The fault is not present. Are there any DTCs stored that have not been diagnosed? | -- | Go to Diagnostic Aids | ||||||||
6 |
Was the resistance of the ECT sensor within specifications? | -- | Go to Step 7 | Go to Step 9 | ||||||
7 |
Was a repair necessary? | -- | Go to Step 11 | Go to Step 10 | ||||||
8 |
Is the action complete? | -- | Go to Step 11 | -- | ||||||
9 | Replace the ECT. Refer to Engine Coolant Temperature Sensor Replacement . Is the action complete? | -- | Go to Step 11 | -- | ||||||
10 | Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- | Go to Step 11 | -- | ||||||
Does the DTC run and pass? | -- | Go to Step 12 | Go to Step 2 | |||||||
12 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK | |||||||
