For 1990-2009 cars

### Circuit Description

The engine coolant temperature (ECT) sensor is a variable resistor that measures the temperature of the engine coolant. The powertrain control module (PCM) supplies 5 volts to the signal circuit. When coolant temperatures are low, resistance is high. When coolant temperatures are high the resistance is low. The PCM uses this input for engine controls and enabling criteria for diagnostics. The PCM will record the amount of time the engine is OFF. At restart the PCM will compare the temperature difference between the ECT and intake air temperature (IAT). If the temperature difference is not within the calculated amount, after the predetermined soak time, this DTC will set.

Before failing this test, the PCM will check for the presence of a block heater.

### Conditions for Running the DTC

• | The ignition is ON.

• | DTCs P0112, P0113, P0117, P0118, P0125, P0128, P0601, P0602, P1621, or P1683 are not set.

• | The vehicle has a minimum soak time of 8 hours.

### Conditions for Setting the DTC

• | If the PCM detects a temperature difference of more than 15°C (27°F) between the ECT and the IAT, the vehicle must be driven for 5 minutes over 24 km/h (15 mph). If the IAT decreases more than 7°C (12.6°F) then a block heater is indicated and the test is aborted. If the IAT temperature does not decrease, a block heater was not detected and this DTC will set.

| OR

• | The temperature difference between the ECT and the IAT at start up is greater than 140°C (252°F) .

| AND

• | The time spent cranking the engine, without starting, is greater than 10 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 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 P0116 is designed to detect an ECT sensor that is skewed high.

• | An IAT sensor that is skewed low could cause this DTC to set.

• | When checking the ECT sensor, the Temperature vs Resistance table should be used in order to determine if a skewed sensor is the problem.

• | If the engine has been allowed to sit overnight, the ECT and IAT temperature should be within the calculated amount.

### Test Description

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

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

2. This step tests for excessive resistance in the IAT sensor circuit.

3. 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. With a scan tool, observe the ECT sensor temperature.

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

138°C (280°F)

Go to Step 4

Go to Step 5

4 |

1. Turn OFF the ignition.
2. Disconnect the IAT sensor.
3. Connect a 3-amp fused jumper wire between the signal circuit and the low reference circuit of the IAT sensor.
4. Turn ON the ignition, with the engine OFF.
5. With a scan tool, observe the IAT sensor temperature.

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

138°C (280°F)

Go to Step 8

Go to Diagnostic Aids

5 |

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. With a scan tool, observe the ECT sensor temperature.

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

138°C (280°F)

Go to Step 6

Go to Step 7

6 |

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 11

--

7 |

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 11

--

8 |

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. Refer to Temperature Versus Resistance .

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

10-90°C (50-194°F)

Go to Step 9

Go to Step 10

9 | Reinstall the ECT sensor. Refer to Engine Coolant Temperature Sensor Replacement . Is the action complete? | -- | Go to Diagnostic Aids | --
10 | Replace the ECT sensor. Refer to Engine Coolant Temperature Sensor Replacement . Did you complete the replacement? | -- | Go to Step 11 | --
11 |

1. Use the scan tool in order to clear the DTCs.
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 12

Go to Step 2

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