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, and the manifold absolute pressure 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 1350 seconds |
| • | The maximum idle time is less than 1013 seconds |
The conditions below are present for all three regions.
| • | No active MAP DTC's |
| • | No active IAT DTC's |
| • | No active ECT DTC's |
| • | No active TP DTC's |
| • | No active O2S DTC's |
| • | No active Fuel Trim DTC's |
| • | No active Injector Control DTC's |
| • | No active Misfire DTC's |
| • | No active CKP DTC's |
| • | No actice IAC DTC's |
| • | The minimum calculated airflow is less than 10 gps 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 tool Freeze Frame/Failure Records. |
Conditions for Clearing the MIL or 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 in order 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 any of the following conditions:
| • | A poor connection |
| • | Rubbed through wire insulation |
| • | A broken wire inside the insulation |
Thoroughly check any circuitry that is suspected of causing the intermittent complaint. Refer to Intermittents and Poor Connections Diagnosis in Wiring Systems.
If a repair is necessary, refer to Wiring Repairs or Connector Repairs in Wiring Systems.
Test Description
The numbers below refer to the step numbers on the Diagnostic Table.
-
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.
-
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.
-
Measure the engine coolant temperature with a thermometer in order to determine what the actual value the ECT sensor should be. Take into consideration if the engine has been operating and if the engine coolant has been warmed.
-
This step simulates a DTC P0118. The PCM and wiring are OK if the PCM senses a change.
-
Program the replacement PCM and perform the crankshaft position system variation learn procedure. Refer to the latest Techline information for PCM programming.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | |||
Are the temperature readings close? | -- | |||
Does the ECT sensor accurately reflect the actual engine coolant temperature? | -- | |||
4 | Is the ECT sensor value close to the IAT sensor reading on the scan tool? | -- | ||
Is the ECT sensor value less than the specified value? | -30°C (-22°F) | |||
6 |
Is the value more than the specified value? | 130°C (266°F) | ||
7 |
Was a repair necessary? | -- | ||
8 |
Is the ECT sensor value more than the specified value? | 130°C (266°F) | ||
9 |
Does the temperature rise more than the specified temperature? | 5°C (9°F) | ||
10 |
Does the DMM read a voltage more than the specified value? | 0.5 volt | Go to Diagnostic Aids | |
11 |
Was a repair necessary? | -- | ||
12 |
Was a repair necessary? | -- | ||
13 | Repair the ECT sensor ground circuit for a short to voltage. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |
|
Important:: The replacement PCM must be programmed. Refer to Powertrain Control Module Replacement/Programming . Replace the PCM. Is the action complete? | -- | -- | ||
15 |
Is the action complete? | -- | -- | |
16 |
Does the scan tool indicate that this diagnostic ran and passed? | -- | ||
17 | Check to see if any additional DTCs are set. Does the scan tool display any DTCs that you have not diagnosed? | -- | Go to the applicable DTC table | System OK |
