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 and a ground for the ECT low reference circuit. When the engine coolant temperature is low, the sensor resistance is high. When the engine coolant temperature is high, the sensor resistance is low. The PCM uses this High Side Coolant Rationality test to determine if the ECT input is skewed high. The internal clock of the PCM will record the amount of time the ignition is OFF. At restart the PCM will compare the temperature difference between the ECT and the intake air temperature (IAT). If the PCM detects that the temperature difference between the ECT and the IAT is not within the calibrated range after the ignition OFF time, DTC P0116 sets.

### Conditions for Running the DTC

• | DTCs P0112, P0113, P0117, P0118, P0502, P0503, P0601, P0603, P0604, P2610 are not set.

• | The ignition is ON.

• | The IAT Sensor parameter is more than 15°C (59°F).

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

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

### Conditions for Setting the DTC

• | The PCM detects a temperature difference between the ECT sensor and the IAT sensor of more than 100°C (180°F) at start up.

| OR

• | The PCM detects a temperature difference at power-up, the ECT is 15°C (27°F) more than the IAT, and the time spent cranking the engine without starting is more than 10 seconds when the fuel level is more than 10 percent.

| OR

• | The PCM detects a temperature difference between the ECT sensor and the IAT sensor of more than 15°C (27°F). The vehicle must then be driven for 5 minutes over 40 km/h (25 mph). If the IAT sensor temperature decreases more than 5°C (9°F), an engine block heater was detected and the test is aborted. If the IAT sensor temperature does not decrease, an engine block heater was not detected and DTC P0116 will set.

### 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.

### Test Description

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

1. A snapshot is the quickest method to capture the data before it changes.

2. An IAT sensor that is skewed low can cause this DTC to set.

3. This step will determine if high resistance has caused this DTC to set.

4. A high resistance short from the signal circuit to the low reference circuit can cause this DTC to set.

Step | Action | Values | Yes | No
--- | --- | --- | --- | ---
Schematic Reference: Engine Controls Schematics Connector End View Reference: Engine Controls Connector End Views or Powertrain Control Module Connector End Views
1 | Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | Go to Diagnostic System Check - Vehicle
2 | Inspect the cooling system coolant level. Is the cooling system coolant low? | -- | Go to Cooling System Draining and Filling | Go to Step 3
3 | Observe and record the ambient air temperature of the vehicle environment using an accurate thermometer. Did you complete the action? | -- | Go to Step 4 | --
4 | Important: The vehicle needs to have been OFF for at least 8 hours for the engine coolant temperature (ECT) and the intake air temperature (IAT) to be at ambient temperature. The vehicle should not have changed environments during this time. Has the engine been OFF for the specified amount of time? | 8 hrs | Go to Step 7 | Go to Step 5
5 |

1. Remove the mass air flow (MAF)/IAT sensor. Refer to Mass Airflow Sensor/Intake Air Temperature Sensor Replacement .
2. Remove the ECT sensor. Refer to Engine Coolant Temperature Sensor Replacement .
3. Place the sensors on a work surface away from any heat source.
4. Allow the sensors to reach the ambient air temperature for 30-60 minutes.

Are the sensors at the ambient temperature?

--

Go to Step 6

--

6 |

1. Connect the MAF/IAT sensor to the electrical connector, but DO NOT install it.
2. Insulate the sensor from any engine heat source.
3. Connect the ECT sensor to the electrical connector, but DO NOT install it.
4. Insulate the sensor from any engine heat source.

Are the sensors connected?

--

Go to Step 7

--

7 | Important: The IAT sensor will start to warm-up as soon as the ignition is turned ON.

1. Turn ON the ignition.
2. Take a snapshot of the Engine Data List with a scan tool. Refer to Scan Tool Snapshot Procedure .
3. Review the snapshot data that was taken with the scan tool.
4. Observe the ECT Sensor parameter with a scan tool.
5. Observe the IAT Sensor parameter with a scan tool.

Is the difference between the ECT Sensor parameter and the IAT Sensor parameter more than the specified value?

15°C (27°F)

Go to Step 8

Go to Testing for Intermittent Conditions and Poor Connections

8 | Observe the recorded IAT Sensor parameter. Is the difference between the IAT Sensor parameter and the ambient air temperature less than the specified value? | 8°C (14°F) | Go to Step 9 | Go to Step 10
9 | Observe the recorded ECT Sensor parameter. Is the difference between the ECT Sensor parameter and the ambient air temperature less than the specified value? | 8°C (14°F) | Go to Testing for Intermittent Conditions and Poor Connections | Go to Step 12
10 |

1. Disconnect the MAF/IAT sensor.
2. Test for an intermittent and for a poor connection at the IAT sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

Did you find and correct the condition?

--

Go to Step 25

Go to Step 11

11 |

1. At the sensor, measure the resistance between the IAT signal and the IAT low reference terminals with a DMM and record the value.
2. Observe the recorded ambient air temperature.
3. Compare the resistance measurement of the IAT sensor to the ambient air temperature using the Temperature vs. Resistance table. Refer to Temperature Versus Resistance .

Is the resistance measurement of the IAT sensor within the specified range?

--

Go to Step 14

Go to Step 22

12 |

1. Disconnect the ECT sensor.
2. Inspect for the following conditions:

• | An ECT sensor leaking engine coolant internally through the sensor

• | Corrosion on the ECT sensor terminals

• | Corrosion on the ECT harness connector terminals

Did you find and correct the condition?

--

Go to Step 25

Go to Step 13

13 |

Important: Do not hold the ECT sensor by the probe.

1. At the sensor, measure the resistance between the ECT signal and the ECT low reference terminals with a DMM and record the value. Refer to Circuit Testing .
2. Observe the recorded ambient air temperature.
3. Compare the resistance measurement of the ECT sensor to the ambient air temperature using the Temperature vs. Resistance table. Refer to Temperature Versus Resistance .

Is the resistance measurement of the ECT sensor within the specified range?

--

Go to Step 15

Go to Step 23

14 | Important: All electrical components and accessories must be turned OFF. Performing this step will disable the diagnostic for 8 hours. Measure the resistance of the IAT signal circuit with a DMM. Is the resistance less than the specified value? | 5 ohms | Go to Step 16 | Go to Step 17
15 | Measure the voltage from the ECT signal circuit to a good ground with a DMM. Is the voltage within the specified range? | 4.9-5.2 V | Go to Testing for Intermittent Conditions and Poor Connections | Go to Step 19
16 | Measure the resistance of the low reference circuit of the IAT sensor with a DMM. Is the resistance less than the specified value? | 5 ohms | Go to Step 20 | Go to Step 18
17 | Test the IAT signal circuit for a high resistance. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 25 | Go to Step 20
18 | Test the IAT low reference circuit for a high resistance. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 25 | Go to Step 20
19 | Test the ECT signal circuit for a high resistance short to ground. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 25 | Go to Step 21
20 | Test for an intermittent and for a poor connection at the powertrain control module (PCM). Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | -- | Go to Step 25 | Go to Step 24
21 | Test for shorted terminals and poor connections at the PCM. Refer to the following:

• | Testing for Intermittent Conditions and Poor Connections

• | Connector Repairs

Did you find and correct the condition?

--

Go to Step 25

Go to Step 24

22 | Replace the MAF/IAT sensor. Refer to Mass Airflow Sensor/Intake Air Temperature Sensor Replacement . Did you complete the replacement? | -- | Go to Step 25 | --
23 | Replace the ECT sensor. Refer to Engine Coolant Temperature Sensor Replacement . Did you complete the replacement? | -- | Go to Step 25 | --
24 | Replace the PCM. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | -- | Go to Step 25 | --
25 | Reassemble the vehicle as necessary. Did you complete the action? | -- | Go to Step 26 | --
26 | Important: This DTC will not run without the ignition being OFF for at least 8 hours.

1. Clear the DTCs with a scan tool.
2. Turn OFF the ignition for 8 hours.
3. Start the engine.
4. Operate the vehicle within the Conditions for Running in 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 27

27 | 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