Circuit Description
When the vehicle is first started, it operates in Open Loop, ignoring the oxygen sensor signal and calculating the air/fuel ratio based on inputs from the engine coolant temperature, throttle position and manifold absolute pressure sensors only. The PCM will begin using the oxygen sensor signal for controlling fuel delivery, Closed Loop, when the following conditions are met:
| • | The oxygen sensor (O2S 1) has varying voltage output showing that it is hot enough to operate properly. |
| • | The engine coolant temperature (ECT) sensor indicates coolant temperature above 20°C (68°F) within 18 minutes after engine start-up. |
Conditions for Setting
| • | The ECT sensor does not show a coolant temperature above 20°C (68°F). |
| • | The engine has run for at least 18 minutes. |
| • | The vehicle speed must be above 8 km/h (5 mph). |
Action Taken
Malfunction indicator lamp (MIL) illuminates after two consecutive driving cycles with the fault active.
Conditions for Clearing the MIL/DTC
| • | The MIL will turn OFF after passing three consecutive diagnostic tests. |
| • | A history DTC will clear after 40 consecutive ignition cycles have occurred without a fault. |
| • | History and current DTCs can be cleared by using a scan tool. |
Diagnostic Aids
| • | When DTC P0125 is set, a skewed ECT sensor is indicated. |
| • | An intermittent may be caused by a poor connection, rubbed through wire insulation, or a wire broken inside the insulation. |
| - | Inspect for poor connection or damaged harness. Inspect the PCM harness for backed out terminals J1-08 and J2-12 for improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection, and damaged harness. |
| - | Perform an intermittent test. If connections and harness check OK, monitor a digital voltmeter connected between the PCM terminal J1-08 and J2-12 while moving related connectors and wiring harness. If a fault is induced, the resistance reading will change. This may help to isolate the location of the malfunction. |
Test Description
The number below refers to the step number on the diagnostic table.
-
Allowing the engine to cool should make the ECT and IAT sensors read close to the ambient temperature. This step checks the initial operation of the ECT sensor.
-
The ECT sensor reading should rise while the engine is running until the engine reaches operating temperature.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics | ||||
1 | Was the On-Board Diagnostic (OBD) System Check perform? | -- | Go to Step 2 | |
Are the temperatures reading close? | -- | Go to Step 3 | Go to DTC P0117 Engine Coolant Temperature (ECT) Sensor Circuit Low Voltage | |
Is the TP sensor voltage less than the specified value? | 20°C (68°F) | Go to Diagnostic Aids | Go to Step 4 | |
4 | Inspect the cooling system coolant level. Fill if low. Was coolant added to the cooling system? | -- | Go to Step 2 | Go to Step 5 |
5 | Compare the ECT value on the scan tool to actual coolant temperature. Are the temperature readings close to within the specified value of each other? | 5°C (41°F) | Go to Step 6 | Go to Step 7 |
6 |
Is the action complete? | -- | -- | |
7 | Replace the ECT sensor and recheck the ECT value on the scan tool. Is the action complete? | -- | -- | |
