For 1990-2009 cars

### Circuit Description

The engine control module (ECM) monitors the temperature of the engine coolant for engine control and as an enabling criteria for some diagnostics. The amount of air flow into an engine is proportional to the amount of heat an engine generates. The ECM monitors the amount of air flow into the engine to calculate engine coolant temperature (ECT). The ECM uses the calculated temperature to determine if the engine has warmed up to the closed loop temperature. If the coolant temperature does not increase normally or does not reach the closed loop temperature, diagnostics that use the ECT as enabling criteria, may not run when expected. If the engine coolant temperature fails to reach the closed loop temperature, before a predetermined amount of air flow enters the engine, this DTC sets.

### DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P0125 Engine Coolant Temperature (ECT) Insufficient for Closed Loop Fuel Control

### Conditions for Running the DTC

• | DTCs P0112, P0113, P0117, P0118, P0480, P0481, P0691, P0692, P0693, and P0694 are not set.

• | The engine is running.

• | DTC P0125 runs continuously once the above conditions are met for approximately 500 seconds.

### Conditions for Setting the DTC

• | The difference between the actual ECT and the calculated ECT is over 10°C (18°F), the calculated ECT depends on the amount of air flow into the engine after start-up.

• | The above conditions exist for up to 4 seconds.

### 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 4 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

• | Use the J 35616-A/BT-8637 Connector Test Adapter Kit for any test that requires probing the ECM harness connector or a component harness connector.

• | The lower connector of the ECM is connector C1 and the upper connector of the ECM is connector C2. Refer to Front of Vehicle/Engine Compartment Component Views.

• | For an intermittent condition, refer to Intermittent Conditions.

### Test Description

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

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

2. This step isolates the condition. If the temperature changes, test for a condition in the low reference circuit. If the temperature remains the same test the signal circuit for a condition.

Step | Action | Values | Yes | No
--- | --- | --- | --- | ---
Schematic Reference: Engine Controls Schematics Connector End View Reference: Component Connector End Views
1 | Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | Go to Diagnostic System Check - Vehicle
2 | Is the engine cooling system lack of enough coolant? | -- | Go to Loss of Coolant | Go to Step 3
3 | Is the customer's concern that the engine does not reach operating temperature or that the heater output is low? | -- | Go to Thermostat Diagnosis | Go to Step 4
4 | Note: Return to this diagnostic procedure after you complete the thermostat diagnosis. Test for the correct operation of the thermostat. Refer to Thermostat Diagnosis. Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 5
5 |

1. Turn OFF the ignition.
2. Disconnect the ECT sensor.
3. Connect a 3-amp fused jumper wire between the signal circuit and the low reference circuit of the ECT sensor.
4. Turn the ignition switch to ON position, with the engine OFF.
5. Observe the ECT sensor parameter with a scan tool.

Is the temperature more than the specified value?

139°C (282°F)

Go to Step 9

Go to Step 6

6 |

1. Connect a 3-amp fused jumper between the signal circuit of the ECT sensor and the engine control module (ECM) housing.
2. Observe the ECT sensor parameter with a scan tool.

Is the temperature more than the specified value?

139°C (282°F)

Go to Step 7

Go to Step 8

7 | Test the low reference circuit of the ECT sensor for high resistance. Refer to Circuit Testing and Wiring Repairs. Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 10
8 | Test the signal circuit of the ECT sensor for high resistance. Refer to Circuit Testing and Wiring Repairs. Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 10
9 | Test for shorted terminals and poor connections at the ECT sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs. Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 11
10 | Test for shorted terminals and poor connections at the ECM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs. Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 12
11 | Replace the ECT sensor. Refer to Engine Coolant Temperature Sensor Replacement. Did you complete the replacement? | -- | Go to Step 13 | --
12 | Replace the ECM. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | -- | Go to Step 13 | --
13 |

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. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.

Did the DTC fail this ignition?

--

Go to Step 2

Go to Step 14

14 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | Go to Diagnostic Trouble Code (DTC) List - Vehicle | System OK