For 1990-2009 cars

### Circuit Description

An engine coolant temperature (ECT) sensor monitors the temperature of the coolant. This input is used by the powertrain control module (PCM) for engine control and as an enabling criteria for some diagnostics.

The air flow coming into the engine is accumulated and used to determine if the engine has been driven within conditions that would allow the engine coolant to heat up normally to the thermostat regulating temperature. If the coolant temperature does not increase normally or does not reach regulating temperature of the thermostat, diagnostics that use engine coolant temperature as enabling criteria may not run when expected.

This diagnostic trouble code (DTC) will set when there has been excessive time to reach a minimum coolant temperature required for Closed Loop fuel control.

### Conditions for Running the DTC

• | This DTC will only run once per ignition cycle within enabling conditions.

• | DTCs P0112, P0113, P0116, P0117, P0118, P1111, P1112, P1114, or P1115 are not set.

• | The minimum intake air temperature is more than -7°C (+19°F).

• | The start-up engine coolant temperature is between -40 to + 40°C (-40 to +104°F).

### Conditions for Setting the DTC

• | The engine run time is over 5 minutes, in order to achieve a Closed Loop temperature of -10°C (14°F).

• | The calibrated amount of air flow has been exceeded.

• | The maximum idle time has been less than 4 minutes.

### Action Taken When the DTC Sets

• | The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.

• | The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

### Conditions for Clearing the MIL/DTC

• | The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.

• | A current DTC, Last Test Failed, clears when the diagnostic runs and passes.

• | A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.

• | Clear the MIL and the DTC with a scan tool.

### Diagnostic Aids

DTC P0125 is designed to detect a skewed ECT sensor.

### Test Description

The numbers below refer to the step numbers on the diagnostic table.

1. This step tests for excessive resistance in the ECT circuit.

2. This step tests for a skewed sensor through the range of temperatures affecting this DTC.

Step | Action | Values | Yes | No
--- | --- | --- | --- | ---
Schematic Reference: Engine Controls Schematics
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | Go to Diagnostic System Check - Engine Controls
2 | Is the cooling system low on coolant? | -- | Go to Loss of Coolant in Engine Cooling | Go to Step 3
3 |

1. Turn OFF the ignition.
2. Disconnect the ECT sensor. Refer to Engine Coolant Temperature Sensor Replacement .
3. Connect a 3-amp fused jumper wire between the signal circuit and the low reference circuit of the ECT sensor.
4. Turn ON the ignition, with the engine OFF.
5. Observe the ECT sensor temperature with a scan tool.

Does the scan tool indicate that the ECT sensor temperature is more than the specified value?

138°C (280°F)

Go to Step 7

Go to Step 4

4 |

1. Turn OFF the ignition.
2. Disconnect the ECT sensor.
3. Connect a 3-amp fused jumper wire between the signal circuit of the ECT sensor and a known good ground.
4. Turn ON the ignition, with the engine OFF.
5. Observe the ECT sensor temperature with a scan tool.

Does the scan tool indicate that the ECT sensor temperature is more than the specified value?

138°C (280°F)

Go to Step 5

Go to Step 6

5 |

1. Test the ECT sensor low reference circuit for a high resistance or an open.
2. Repair the circuit as necessary. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 10

--

6 |

1. Test the ECT sensor signal circuit for a high resistance or an open.
2. Repair the circuit as necessary. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 10

--

7 |

1. Remove the ECT sensor.
2. Suspend the ECT sensor and a thermometer in a pan of water.
3. Place the pan on a burner or hot plate.
4. Test the resistance of the ECT sensor through the specified range of temperatures.

Does the resistance and temperature closely match the Temperature vs Resistance table?

10-90°C (50-194°F)

Go to Step 8

Go to Step 9

8 | Reinstall the ECT sensor. Refer to Engine Coolant Temperature Sensor Replacement . Is the action complete? | -- | Go to Thermostat Diagnosis in Engine Cooling | --
9 | Replace the ECT sensor. Refer to Engine Coolant Temperature Sensor Replacement . Did you complete the replacement? | -- | Go to Step 10 | --
10 |

1. Clear the DTCs with a scan tool.
2. Turn OFF the ignition for 30 seconds.
3. Start the engine.
4. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC run and pass?

--

Go to Step 11

Go to Diagnostic Aids

11 | Observe the stored information, Capture Info, with a scan tool. Does the scan tool display any DTCs that you have not diagnosed? | -- | Go to Diagnostic Trouble Code (DTC) List | System OK