Circuit Description
When the vehicle is first started, the engine operates in an Open Loop operation, ignoring the oxygen sensor (O2S 1) 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 O2S 1 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 when the unit 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
| • | Engine run time is between 30 seconds and 30 minutes. |
| • | Calculated average flow is more than 20 g/sec. |
| • | Vehicle traveled more than 0.5 miles. |
| • | Vehicle speed is more than 40 km/h (25 mph). |
| • | IAT is more than -7°C (19°F). |
| • | Start up ECT is less than 35°C (95°F). |
| • | None of the following DTCs set: |
| 105, 107, 108, 112, 113, 117, 118, 122, 123, 130 ,131, 132, 169, 171, 172, 178, 179, 201, 202, 203, 204, 300, 325, 336, 420, 440, 442, 446, 452, 453, 502, 503, 1441. |
Conditions for Setting the DTC
If actual accumulated air flow is more than a predicted air flow before engine coolant reaches 40°C (104°F).
Action Taken When the DTC Sets
| • | The malfunction indicator lamp (MIL) will illuminate after 2 consecutive ignition cycles in which the diagnostic runs with the malfunction present. |
| • | The PCM will record the operating conditions at the time that the diagnostic fails. This information will store in the Freeze Frame and Failure Records buffers. |
| • | A history DTC stores. |
Conditions for Clearing the MIL/DTC
| • | The MIL will turn OFF after 3 consecutive ignition cycles in which the diagnostic runs without a fault. |
| • | A history DTC will clear after 40 consecutive warm up cycles without a fault. |
| • | A scan tool can clear the DTCs. |
Diagnostic Aids
A skewed ECT sensor or a stuck open thermostat will cause DTC P0125 to set.
If the vehicle is in a cold climate and the DTC will not reset in the garage, you may have a partially stuck open thermostat. For thermostat diagnosis refer to Thermostat Diagnosis in Engine Cooling.
An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside the insulation.
| • | Check for a poor connection or a damaged PCM harness. Inspect the ECT sensor signal circuit and the ground circuit terminals 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. If the connections and the harness check 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 below in order to evaluate the possibility of a skewed sensor. Refer to Temperature Versus Resistance . |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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The Powertrain OBD System Check prompts you to complete some of the basic checks and to store the Freeze Frame and Failure Records data on the scan tool if applicable. This creates an electronic copy of the data captured when the malfunction occurred. The scan tool stores this data for later reference.
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Allow the engine to fully cool. The ECT sensor and the IAT sensor will read close to the ambient temperature in order to check for a possible skewed ECT sensor.
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This step simulates a DTC P0118. The PCM and wiring are OK if the PCM senses a change.
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This step simulates a DTC P0117. The PCM and wiring are OK if the PCM senses a change.
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Reprogram the replacement PCM and perform the Crankshaft Position System Variation Learn Procedure. Refer to the latest Techline information for PCM programming.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | |||
Are the temperature readings close? | -- | |||
3 |
Does the ECT sensor accurately reflect the actual engine coolant temperature? | -- | ||
4 | Check the cooling system level. Is the coolant level low? | -- | Go to Loss of Coolant in Engine Cooling | |
5 |
Does the scan tool indicate that this diagnostic Ran and Passed? | -- | Go to Diagnostic Aids | |
6 |
Caution: To avoid being burned, do not remove the radiator cap or surge tank cap while the engine is hot. The cooling system will release scalding fluid and steam under pressure if radiator cap or surge tank cap is removed while the engine and radiator are still hot. Is the actual coolant temperature near the scan tool ECT temperature? | -- | Go to Thermostat Diagnosis in Engine Cooling | |
Is the ECT sensor value less than the specified value? | -30°C (-22°F) | |||
Is the ECT sensor value more than the specified value? | 130°C (266°F) | |||
9 |
Is the action complete? | -- | -- | |
10 |
Was a repair necessary? | -- | ||
11 |
Was a repair necessary? | -- | ||
|
Important: The replacement PCM must be programmed. Replace the PCM. Refer to Powertrain Control Module Replacement/Programming . Is the action complete? | -- | -- | ||
13 |
Does the scan tool indicate that this diagnostic Ran and Passed? | -- | ||
14 | Check to see if any additional DTCs are set. Does the scan tool display any DTCs that you have not diagnosed? | -- | Go to applicable DTC table | System OK |
