Circuit Description
The engine coolant temperature (ECT) sensor is a thermistor. A thermistor is a resistor whose value varies with temperature. The ECT sensor resistance is high when the coolant temperature is cold, and the ECT sensor 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 Running the DTC
| • | The engine has been running for at least 20 minutes. |
| • | The vehicle has been driven at speeds of 50 km/h (30 mph) or more at least once since engine start. |
Conditions for Setting the DTC
Engine coolant temperature, as indicated by the ECT sensor, variation is less than the expected value.
Action Taken When the DTC Sets
| • | The PCM illuminates the malfunction indicator lamp (MIL) after two 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 MIL turns off after three consecutively passing trips without a fault present. |
| • | A History DTC clears after 40 consecutive warm-up cycles without a fault. |
| • | Perform the scan tool Clear DTC Information function. |
Diagnostic Aids
Check for the following conditions:
| • | If a DTC P0106 and a DTC P0121 are also set, the malfunction may be in the sensor ground circuit. |
| • | Check for the proper operation of the engine cooling system, including the correct coolant level. Refer to Engine Fails To Reach Normal Operating Temperature in Engine Cooling. |
| • | A faulty 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 any suspect thermostat. Refer to Thermostat Diagnosis in Engine Cooling. |
| • | Use the Temperature vs Resistance table in order to evaluate the possibility of a shifted (incorrectly calibrated) ECT sensor. A shifted sensor may result in a DTC P0116. Refer to Temperature Versus Resistance . |
| • | Check for a faulty electrical connection to the PCM. |
If a DTC P0116 is intermittent, driving the vehicle under the following conditions can verify whether the fault is present. Perform the scan tool clear DTC information function. Road test the vehicle while monitoring the DTC P0116 diagnostic on the scan tool under the Not Ran Since Code Cleared selection in the DTC Information menu. If a DTC P0116 appears in the Not Ran Since Code Cleared list, the P0116 diagnostic has not yet run. When the DTC P0116 does not appear in the Not Ran Since Code Cleared list, the P0116 diagnostic has run. If the MIL is NOT ILLUMINATED, and there is no PENDING DTC Status in DTC Information, the P0116 diagnostic has passed. DTCs MUST BE CLEARED in order to view the CURRENT STATUS of the Not Ran Since Code Cleared list. DO NOT FORGET that the Not Ran Since Code Cleared list only indicates that the test has run, not whether the test passed or failed. The DTC Information screen must be checked for CURRENT or PENDING status, in order to determine the outcome of the diagnostic test involved.
An intermittent malfunction may be caused by a fault in the ECT sensor electrical circuit. Inspect the wiring harness and components for any of the following conditions:
| • | Backed out terminals |
| • | Improper mating of terminals |
| • | Broken electrical connectors locks |
| • | Improperly formed or damaged terminals |
| • | Faulty terminal to wire connections |
| • | Physical damage to the wiring harness |
| • | A broken wire inside the insulation |
| • | Corrosion of electrical connections, splices, or terminals |
Repair any electrical circuit faults that were found. Refer to Wiring Repairs in Wiring Systems.
If a 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 in the diagnostic table.
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The OBD System Check 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.
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This step checks for a faulty engine coolant temperature (ECT) sensor or ECT sensor circuit.
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This step checks the integrity of the ECT sensor input circuit.
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This step checks the integrity of the ECT sensor ground circuit.
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This step checks the integrity of the ECT sensor input circuit.
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A cooling system that prevents the engine from warming up properly and reaching the correct engine operating temperature within a specified time can cause a DTC P0116 to set. A thermostat that stays open slightly can cause a DTC P0116 to set.
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This step determines if DTC P0116 is the result of a hard failure or an intermittent condition.
Step | Action | Value(s) | Yes | No | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | |||||||||||||||
2 | Check for DTC P0117 or DTC P0118 with a scan tool. Is DTC P0117 or DTC P0118 present? | -- | Go to DTC P0117 Engine Coolant Temperature (ECT) Sensor Circuit Low Voltage or to DTC P0118 Engine Coolant Temperature (ECT) Sensor Circuit High Voltage | |||||||||||||
Is the ECT sensor value near the actual coolant temperature? | -- | |||||||||||||||
Does the ECT equal the specified value? | -40 C (-40°F) | |||||||||||||||
Does the ECT equal the specified value? | 164°C (327°F) | |||||||||||||||
Does the ECT equal the specified value? | 164°C (327°F) | |||||||||||||||
7 | Repair the open or electrical resistance in the ECT sensor ground circuit. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | ||||||||||||||
8 |
Was a repair necessary? | -- | ||||||||||||||
9 |
Was a repair necessary? | -- | ||||||||||||||
10 |
Important: The replacement PCM must be programmed. Replace the PCM. Refer to Powertrain Control Module Replacement/Programming . Is the action complete? | -- | -- | |||||||||||||
Was a repair necessary? | -- | |||||||||||||||
Does DTC P0116 set? | -- | Go to Diagnostic Aids | ||||||||||||||
13 | Replace the ECT sensor. Refer to Engine Coolant Temperature Sensor Replacement . Is the action complete? | -- | -- | |||||||||||||
14 |
Are any DTCs displayed on scan tool? | -- | System OK |
