For 1990-2009 cars

### Circuit Description

The DTC P0116 Engine Coolant Temperature (ECT) Sensor Performance diagnostic monitors the sensor activity. The ECT sensor is a thermistor. A thermistor is a resistor whose value varies with temperature. The ECT sensors resistance is high when the coolant temperature is cold, and the ECT sensors resistance is low when the coolant temperature is warm. The ECT sensor is wired in series with a fixed resistor in the powertrain control module (PCM). The PCM applies 5 volts to the ECT sensor. The PCM monitors the voltage across the ECT sensor and converts the voltage into a temperature reading. The PCM will receive a high voltage input when the coolant temperature is cold. The PCM will receive a low voltage input when the coolant temperature is warm. A DTC P0116 may set if the ECT sensor voltage does not indicate that the engine coolant temperature has increased sufficiently during engine operation.

### Conditions for Setting the DTC

• | The ECT or the intake air temperature (IAT) is less than -6.7°C (20°F) at engine start up, and the ECT sensor is 35°C (95°F) or less after running for 20 minutes.

| OR

• | The ECT or the IAT is between -6.7 to +10°C (20-50°F) at engine start up, and the ECT sensor is 35°C (95°F) or less after running for 5 minutes.

| OR

• | The ECT or the IAT is more than 10°C (50°F) at engine start up, and the ECT sensor is 35°C (95°F) or less after running for 2 minutes.

### Action Taken When the DTC Sets

• | The PCM illuminates the malfunction indicator lamp (MIL) after 2 consecutive ignition cycles in which the diagnostic runs with the fault active.

• | The PCM records the operating conditions at the time the diagnostic fails. This information is stored in the Freeze Frame buffer.

### Conditions for Clearing the MIL/DTC

• | The malfunction indicator lamp (MIL) turns OFF after 3 consecutively passing trips without a fault present.

• | A History DTC clears after 40 consecutive warm-up cycles without a fault.

• | Use the scan tool Clear DTC Information function.

### Diagnostic Aids

Check for the following conditions:

• | If DTCs P0105, P0110, P0115, and P0120 are also set, the malfunction may be in a sensor ground circuit.

• | If DTCs P0115 and P0116 are both set the ECT sensor circuit may be open or shorted. Perform the DTC P0115 diagnostic table first.

• | Check for the proper operation of the engines cooling system, including the correct coolant level.

• | A faulty thermostat that stays open slightly can cause DTC P0116 to set in cold weather when the vehicle is started and let sit while warming up. Replace any suspect thermostat.

• | Use the Temperature vs Resistance table in order to evaluate the possibility of a shifted ECT sensor. A shifted sensor could result in DTC P0116. Refer to Temperature Versus Resistance .

• | Check for a faulty electrical connection to the PCM.

An intermittent malfunction may be caused by a fault in the ECT sensor electrical circuit. Inspect the wiring harness and components for an intermittent condition. Refer to Intermittent Conditions .

Repair any electrical circuit faults that were found. Refer to Wiring Repairs in Wiring Systems.

If DTC P0116 cannot be duplicated, the information included in the Freeze Frame data can be useful in determining the vehicle operating conditions when the DTC was first set.

### Test Description

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

1. The Diagnostic System Check-Engine Controls prompts the technician to complete some basic checks and store the Freeze Frame data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.

2. This step checks for a faulty ECT sensor or ECT sensor circuit.

3. This step checks the integrity of the ECT sensor input circuit.

4. This step checks the integrity of the ECT sensor ground circuit.

5. This step checks the integrity of the ECT sensor input circuit.

6. A cooling system that prevents the engine from warming up properly and reaching the correct engine operating temperature within a set run time can cause a DTC P0116 to set. A thermostat that stays open slightly can cause a DTC P0116 to set in cold weather when the vehicle is started and let sit while warming up. Replace the thermostat if suspect .

7. This step determines if DTC P0116 is the result of a hard failure or an intermittent condition.

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 | Check for DTC P0115 with a scan tool. Is DTC P0115 set? | -- | Go to DTC P0115 | Go to Step 3
3 |

1. Measure the actual coolant temperature.
2. Turn ON the ignition, with the engine OFF.
3. Observe the ECT sensor parameter on the scan tool.

Is the ECT sensor value displayed near the actual coolant temperature?

--

Go to Step 11

Go to Step 4

4 |

1. Disconnect the ECT sensor electrical connector.
2. Observe the ECT sensor parameter on the scan tool.

Does the engine coolant temperature equal the specified value?

-40 C (-40°F)

Go to Step 5

Go to Step 8

5 |

1. Disconnect the ECT sensor electrical connector.
2. Jump the ECT sensor input circuit and the ground circuit together at the ECT sensor harness connector.
3. Observe the ECT sensor parameter on the scan tool.

Does the engine coolant temperature equal the specified value?

140°C (284°F)

Go to Step 13

Go to Step 6

6 |

1. Jump the ECT sensor input circuit to chassis ground.
2. Observe the ECT sensor parameter on the scan tool.

Does the engine coolant temperature equal the specified value?

140°C (284°F)

Go to Step 7

Go to Step 8

7 | Repair the open or high resistance in the ECT sensor ground circuit. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | Go to Step 14 | Go to Step 9
8 |

1. Turn OFF the ignition.
2. Disconnect the PCM electrical connector C2.
3. Check the ECT sensor input circuit for a short or a high electrical resistance.
4. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a repair necessary?

--

Go to Step 14

Go to Step 9

9 |

1. Check for a faulty connection at the PCM and the ECT electrical connectors.
2. Repair as necessary.

Was a repair necessary?

--

Go to Step 14

Go to Step 10

10 | Replace the PCM. Refer to Powertrain Control Module Replacement . Is the action complete? | -- | Go to Step 14 | --
11 |

1. Inspect the engine cooling system for any of the following conditions:

• | A faulty thermostat

• | A low coolant level

• | An incorrect coolant

• | Any faulty cooling system operation

2. Repair as necessary.

Was a repair necessary?

--

Go to Step 14

Go to Step 12

12 |

1. Perform the scan tool Clear DTC Information function.
2. Place the vehicle into Check Mode, using the scan tool.
3. Operate the vehicle within the Freeze Frame conditions as specified.

Does DTC P0116 set?

--

Go to Step 13

Go to Diagnostic Aids

13 | Replace the ECT sensor. Refer to Engine Coolant Temperature Sensor Replacement . Is the action complete? | -- | Go to Step 14 | --
14 |

1. Perform the scan tool Clear DTC Information function and road test the vehicle within the Freeze Frame conditions that set the DTC.
2. Review the scan tool data and check for DTCs. The repair is complete if no DTCs are stored.

Are any DTCs displayed on scan tool?

--

Go to Step 15

Go to Step 2

15 | 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