Circuit Description
When the vehicle is first started, it operates in Open Loop, ignoring the oxygen sensor (O2S) signal and calculating the fuel/air ratio based on inputs from the engine coolant temperature (ECT), throttle position (TP), and manifold absolute pressure (MAP) sensors only. The engine control module (ECM) will begin using the O2S signal for controlling 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 O2S has a varying voltage output showing that it is hot enough to operate properly. |
| • | The ECT has increased a minimum amount based on ECT at engine start up. |
Conditions for Setting the DTC
| • | The engine is running. |
| • | DTCs P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0122, P0123, P0201, P0202, P0203, P0204, P0351, P0352, and P0502 are not set. |
| • | Start-up coolant temperature is less than or equal to 32°C (89.6°F). |
| • | If the ambient temperature is less than or equal to 10°C (50°F), the accumulated airflow is greater than 1.2 kg (2.7 lb) and the accumulated idle time is less than 90 seconds. |
| • | If ambient temperature is between -7°C to +10°C (+20°F to +50°F), the accumulated airflow is greater than 3.2 kg (7.1 lb) and the accumulated idle time is less than 225 seconds. |
| • | If ambient temperature is between -38°C to -7°C (-36.4°F to +20°F), the accumulated airflow is greater than 5 kg (11 lb) and the accumulated idle time is less than 675 seconds. |
| • | If ambient temperature is greater than 10°C (50°F), the time for coolant to reach a stabilized Closed Loop value, 21°C (69.8°F), is greater than 2 minutes. |
| • | If ambient temperature is between than -7°C to +10°C (+20°F to +50°F), the time for coolant to reach a stabilized Closed Loop value, 16°C (60.8°F), is greater than 5 minutes. |
| • | If ambient temperature is between than -38°C to -7°C (-36.4°F to +20°F), the time for coolant to reach a stabilized Closed Loop value, 20°C (68°F), is greater than 15 minutes. |
Action Taken When the DTC Sets
| • | The malfunction indicator lamp (MIL) will illuminate. |
| • | The ECM will record operating conditions at the time the diagnostic fails. This information will be stored in the Freeze Frame and Failure Records buffers. |
| • | A history DTC is stored. |
| • | Both coolant fans turn ON. |
Conditions for Clearing the MIL/DTC
| • | The MIL will turn OFF after 4 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. |
| • | The DTCs can be cleared by using the scan tool. |
| • | Disconnect the ECM battery feed for more than 10 seconds. |
Diagnostic Aids
When DTC P0125 is set, a skewed ECT sensor or a stuck open thermostat is indicated.
An intermittent may be caused by a poor connection, rubbed-through wire insulation, or a wire broken inside the insulation.
Inspect for a poor connection or damaged ECM harness. Inspect the ECT sensor signal circuit and ground circuit terminals for the following conditions:
| • | Improper mating |
| • | Broken locks |
| • | Improperly formed |
| • | Damaged terminals |
| • | A poor terminal-to-wire connection |
| • | A damaged harness |
Perform an intermittent test. If the connections and the harness are OK, monitor a digital voltmeter connected between the 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 to isolate the location of the malfunction.
Use the Temperature vs. Resistance table to evaluate the possibility of a skewed sensor. Refer to Temperature Versus Resistance .
Step | Action | Values | Yes | No |
|---|---|---|---|---|
1 | Perform the Diagnostic System Check-Engine Controls. Was the check performed? | -- | Go to Step 2 | |
2 |
Are the temperature readings close? | -- | Go to Step 4 | Go to Step 3 |
3 |
Does the ECT sensor accurately reflect the actual engine coolant temperature? | -- | Go to Step 4 | Go to Step 11 |
4 |
Is the ECT sensor value less than the specified value? | -30°C (-22°F) | Go to Step 5 | Go to Step 8 |
5 | Jumper the ECT sensor signal circuit terminal 1 and the sensor ground circuit terminal 2 at the connector. Is the ECT sensor value greater than the specified value? | 130°C (266°F) | Go to Step 6 | Go to Step 7 |
6 | Inspect for proper cooling system operation and repair as needed. Is the repair complete? | -- | Go to Step 12 | Go to Diagnostic Aids |
7 | Inspect the ECT sensor connector terminals 2 and 1 and the engine control module (ECM) electrical connector terminals M28 and M64 for poor connectors or malfunctioning terminals and repair as needed. Is the repair complete? | -- | Go to Step 12 | Go to Step 8 |
8 | Inspect the ECT sensor signal circuit for an open or short to ground and repair as needed. Is the repair complete? | -- | Go to Step 12 | Go to Step 9 |
9 | Inspect the ECT ground circuit for an open and repair as needed. Is the repair complete? | -- | Go to Step 12 | Go to Step 10 |
10 |
Is the replacement complete? | -- | Go to Step 12 | -- |
11 | Replace the ECT sensor. Is the replacement complete? | -- | Go to Step 12 | -- |
12 |
Does the scan tool indicate that this diagnostic has run and passed? | -- | Go to Step 13 | Go to Step 2 |
13 | Check if any additional DTCs are set. Are any DTCs displayed that have not been diagnosed? | -- | System OK |
