Circuit Description
When the vehicle is first started, the engine operates in an Open Loop operation, ignoring the oxygen sensor signal and calculating the air/fuel ratio based on inputs from the engine coolant temperature (ECT), the throttle position (TP) and the manifold absolute pressure (MAP) sensors only. The powertrain control module (PCM) will begin by using the oxygen sensor signal for controlling the fuel delivery (Closed Loop) when the following conditions are met:
| • | The engine has run a minimum amount of time based on ECT at engine start up. |
| • | The oxygen sensor (O2S 1) has a varying voltage output showing that it is hot enough to operate properly. |
| • | The ECT has increased a minimum amount based on the ECT at engine start up. |
Conditions for Running the DTC
Region 1 - Ambient Temperature Above 10°C (50°F)
| • | The start up engine coolant temperature is above 10°C (50°F). |
| • | The IAT is more than 10°C (50°F). |
| • | The ECT is more than 10°C (50°F). |
| • | The engine run time is more than 120 seconds. |
| • | The maximum idle time is less than 90 seconds. |
OR
Region 2 - Ambient Temperature Above -7°C (20°F)
| • | The start up engine coolant temperature is between -7°C (20°F) and 10°C (50°F). |
| • | The IAT is more than -7°C (20°F). |
| • | The ECT is more than -7°C (20°F). |
| • | The engine run time is more than 300 seconds. |
| • | The maximum idle time is less than 225 seconds. |
OR
Region 3 - The Start Up Engine Coolant Temperature Below -7°C (20°F)
| • | The IAT is more than -7°C (20°F). |
| • | The ECT is less than -7°C (20°F). |
| • | The engine run time is more than 1,350 seconds. |
| • | The maximum idle time is less than 1,013 seconds. |
The conditions below are present for all three regions.
| • | No active MAP DTCs |
| • | No active IAT DTCs |
| • | No active ECT DTCs |
| • | No active TP DTCs |
| • | No active oxygen sensor DTCs |
| • | No active fuel trim DTCs |
| • | No active injector control DTCs |
| • | No active misfire DTCs |
| • | No active CKP DTCs |
| • | No active IAC DTCs |
| • | No active system voltage DTCs |
| • | The minimum calculated airflow is less than 10 grams per second to be considered at idle for all three temperature regions. |
| • | The IAT is more than -7°C (20°F). |
| • | The start up engine coolant temperature below 151°C (304°F) |
Conditions for Setting the DTC
The conditions below are present for all three regions:
| • | The ECT is less than 40°C (113°F). |
| • | The vehicle is in an Open Loop operation. |
Action Taken When the DTC Sets
| • | The control module illuminates the malfunction indicator lamp (MIL) if a failure is detected during 2 consecutive key cycles. |
| • | The control module sets the DTC and records the operating conditions at the time the diagnostic failed. The failure information is stored in the scan tools Freeze Frame and Failure Records. |
Conditions for Clearing the MIL/DTC
| • | The control module turns OFF the MIL after 3 consecutive drive trips when the test has Run and Passed |
| • | A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles. A warm up cycle occurs when the coolant temperature has risen 22°C (40°F) from the startup coolant temperature and the engine coolant reaches a temperature that is more than 70°C (158°F) during the same ignition cycle. |
| • | Use a scan tool to clear the DTCs. |
Diagnostic Aids
A skewed ECT sensor or a stuck open thermostat will cause DTC P0125 to set.
An intermittent may be caused by a poor connection, rubbed through wire insulation or a broken wire inside the insulation.
| • | Inspect for a poor connection or a damaged PCM harness. Inspect the ECT sensor signal circuit and the ground circuit for the following conditions: |
| - | Improper mating |
| - | Broken locks |
| - | Improperly formed connectors |
| - | Damaged terminals |
| - | A poor terminal to wire connection |
| - | Damaged harness |
| • | Perform an intermittent test. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems. If the connections and the harness test OK, monitor a digital voltmeter connected between ECT sensor signal circuit and ground circuit terminals while moving the related connectors and the wiring harness. If a fault is induced, the resistance reading will change. This may help in order to isolate the location of the malfunction. |
| • | Use the Temperature vs. Resistance table in order to evaluate the possibility of a skewed sensor. Refer to Temperature Versus Resistance . |
Test Description
The numbers below refers to the step numbers on the diagnostic table:
-
Allow the engine to fully cool. The ECT sensor and the IAT sensor will read close to each other and to the ambient temperature. This will test for a possible skewed ECT sensor.
-
This step simulates a DTC P0118. The PCM and wiring are OK if the PCM senses a change.
-
The replacement PCM must be programmed and the Crankshaft Position System Variation Learn procedure must be performed.
Step | Action | Values | Yes | No | ||||
|---|---|---|---|---|---|---|---|---|
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | ||||||
2 | Are any other ECT DTCs set? | -- | ||||||
Are the parameters within the specified value of each other? | 3°C (5°F) | |||||||
4 |
Are the parameters within the specified value of each other | 3°C (5°F) | ||||||
Does the ECT sensor parameter read less than the specified value? | -30°C (-22°F) | |||||||
6 |
Does the ECT sensor parameter read more than the specified value? | 130°C (266°F) | ||||||
7 |
Does the ECT parameter rise more than the specified value? | 5°C (9°F) | Go to Diagnostic Aids | Go to Thermostat Diagnosis in Engine Cooling | ||||
8 |
Did you find and correct the condition? | -- | ||||||
9 |
Did you find and correct the condition? | -- | ||||||
10 |
Did you find and correct the condition? | -- | ||||||
11 | Replace the ECT sensor. Refer to Engine Coolant Temperature Sensor Replacement . Did you complete the replacement? | -- | -- | |||||
|
Important:: The replacement PCM must be programmed. Replace the PCM. Refer to Powertrain Control Module Replacement/Programming . Did you complete the replacement? | -- | -- | ||||||
13 |
Does the DTC reset? | -- | System OK |
