Circuit Description
The DTC P0118 Engine Coolant Temperature (ECT) Sensor Circuit High Voltage diagnostic detects an out of range sensor signal. The ECT sensor is a thermistor. A thermistor is a resistor whose value varies with the temperature. The electrical resistance of the ECT sensor is high when the coolant temperature is cold, and the 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 voltage measured by the PCM will be high when the coolant temperature is cold, and low when the coolant temperature is warm.
Temperature | ECT Resistance | ECT Signal Voltage |
|---|---|---|
Cold | High | High |
Warm | Low | Low |
Conditions for Running the DTC
| • | The ignition is ON or the engine is running. |
| • | DTC P0118 runs continuously once the above condition has been met. |
Conditions for Setting the DTC
The temperature input is less than -40°C (-40°F) for at least 0.5 seconds.
Action Taken When the DTC Sets
| • | The PCM illuminates the malfunction indicator lamp (MIL). |
| • | The PCM records the operating conditions at the time the diagnostic fails. This information is stored in the Freeze Frame buffer. |
| • | The PCM enters the Fail Safe Function in which the coolant temperature will default to 80°C (176°F). |
Conditions for Clearing the MIL/DTC
| • | The 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 a faulty electrical connection to the PCM. |
| • | Check for the proper operation of the engine cooling system and verify the correct coolant level. |
| • | Use the Temperature vs Resistance table in order to evaluate the possibility of a shifted ECT sensor. A shifted sensor could result in a DTC P0118. Refer to Temperature Versus Resistance . |
| • | 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 a DTC P0118 cannot be duplicated, the information included in the Freeze Frame data can be useful in determining vehicle operating conditions when the DTC was first set. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
The Diagnostic System Check - Vehicle 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.
-
This step checks for a high voltage on the input circuit. If the scan tool reads -40°C (-40°F), the input circuit is open.
-
This step determines if DTC P0118 is the result of a hard failure or an intermittent condition.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics Connector End View Reference: Powertrain Control Module Connector End Views or Engine Controls Connector End Views | ||||
Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | ||
Select the ECT sensor parameter on the scan tool. Is the ECT sensor value more than or equal to the specified value? | -40°C (-40°F) | Go to Step 4 | Go to Step 3 | |
Does the DTC run and pass? | -- | Go to Diagnostic Aids | Go to Step 4 | |
4 |
Is the ECT sensor value more than or equal to the specified value? | 140°C (284°F) | Go to Step 6 | Go to Step 5 |
5 | Jump the ECT input circuit at the ECT sensor harness connector to chassis ground. Is the ECT sensor value more than or equal to the specified value? | 140°C (284°F) | Go to Step 7 | Go to Step 8 |
6 |
Did you find and correct a condition? | -- | Go to Step 12 | Go to Step 10 |
7 |
Did you find and correct a condition? | -- | Go to Step 12 | Go to Step 9 |
8 |
Did you find and correct a condition? | -- | Go to Step 12 | Go to Step 9 |
9 |
Did you find and correct a condition? | -- | Go to Step 12 | Go to Step 11 |
10 | Replace the ECT sensor. Refer to Engine Coolant Temperature Sensor Replacement . Did you complete the replacement? | -- | Go to Step 12 | -- |
11 | Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- | Go to Step 12 | -- |
12 |
Does the DTC run and pass? | -- | Go to Step 13 | Go to Step 2 |
13 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK | |
