Circuit Description
The engine coolant temperature (ECT) sensor is a thermistor that controls signal voltage to the powertrain control module (PCM). When the engine is cold, the sensor resistance is high, therefore the PCM will see high signal voltage. As the engine warms, sensor resistance becomes less and voltage drops. The voltage measured across the thermistor is interpreted as a temperature.
Conditions for Running the DTC
| • | The PCM performs this diagnostic trouble code (DTC) diagnostic continuously. |
| • | The engine operation time is more than 8 minutes. |
Conditions for Setting the DTC
| • | The engine coolant temperature is less than or equal to -40°C (-40°F). |
| • | All of the diagnostic set conditions are met for 2 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
Check harness routing for a potential short to voltage. After the engine is started, the ECT temperature should rise steady to about 85°C (185°F). A skewed sensor could result in poor driveability complaints. Refer to Temperature Versus Resistance .
An intermittent may be caused by any of the following conditions:
| • | A poor connection |
| • | Rubbed through wire insulation |
| • | A broken wire inside the insulation |
Thoroughly check any circuitry that is suspected of causing the intermittent complaint. Refer to Testing for Electrical Intermittents in Wiring Systems.
If a repair is necessary, then refer to Wiring Repairs or Connector Repairs in Wiring Systems.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
This step determines if DTC P0118 is a hard failure or an intermittent condition.
-
This step will determine if there is a wiring problem or a malfunctioning PCM.
-
This step determines if there is a short to voltage on the signal circuit. A short to voltage increases current flow through the sensor which overwhelms the sensor. This does not allow the sensor to pull down the circuit to the correct voltage and thus display the correct temperature.
-
After repairing the short to voltage, check the sensor for proper operation.
Step
| Action | Values | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics | ||||
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | |
Does the ECT display a temperature colder than the specified value? | -30°C (-22°F) | Go to Step 3 | Go to Step 5 | |
Does the scan tool display an ECT temperature more than the specified value? | 151°C (303°F) | Go to Step 6 | Go to Step 4 | |
4 | Jumper the ECT sensor signal circuit to a known good ground. Does the scan tool display an ECT temperature more than the specified value? | 151°C (303°F) | Go to Step 7 | Go to Step 8 |
5 | The DTC is intermittent. If no other DTCs are stored, refer to Diagnostic Aids. Are there any other DTCs stored? | -- | Go to Diagnostic Aids | |
6 |
Did you find and correct the condition? | -- | Go to Step 14 | Go to Step 9 |
7 |
Did you find and correct the condition? | -- | Go to Step 14 | Go to Step 11 |
8 |
Did you find and correct the condition? | -- | Go to Step 14 | Go to Step 11 |
With a DMM set to the mA scale, measure the current at the ECT harness connector terminals. Does the current measure less than the specified value? | 48 mA | Go to Step 12 | Go to Step 10 | |
Repair the short to voltage on the ECT signal circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 14 | -- | |
11 | Inspect the PCM connectors for proper connections and replace the terminals, if necessary. Refer to Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 14 | Go to Step 13 |
12 | Replace the ECT sensor. Refer to Engine Coolant Temperature Sensor Replacement . Did you complete the replacement? | -- | Go to Step 14 | -- |
13 | Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- | Go to Step 14 | -- |
14 |
Does the DTC run and pass? | -- | 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? | -- | System OK | |
