Circuit Description
The DTC P0118 Engine Coolant Temperature (ECT) Sensor Circuit High Voltage diagnostic monitors the ECT 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.
Condition for Running the DTC
The ignition is ON or the engine is running.
Conditions for Setting the DTC
| • | The ignition is ON. |
| • | ECT sensor signal indicates an engine coolant temperature -40°C (-40°F). |
| • | Above condition is met for at least 5 seconds. |
Action Taken When the DTC Sets
| • | The malfunction indicator lamp (MIL) will illuminate. |
| • | The PCM will record operating conditions at the time the diagnostic fails. This information will be stored in the Freeze Frame buffer. |
| • | The PCM will enter the Fail-Safe Function and assume the engine coolant temperature is 30°C (86°F). |
Conditions for Clearing the MIL/DTC
| • | The MIL will turn OFF after three consecutively passing cycles without a fault present. |
| • | A History DTC will clear after 40 consecutive warm-up cycles without a fault. |
| • | DTCs can be cleared by using a scan tool or by disconnecting the PCM battery feed. |
Diagnostic Aids
Check for any of the following conditions:
| • | A damaged wiring harness -- Inspect the wiring harness for damage. If the harness appears to be OK, observe the ECT display on the scan tool while moving connectors and wiring harnesses related to the ECT sensor. A change in the ECT display will indicate the location of the fault. |
| • | When replacing the ECT sensor the Temperature to Resistance Value scale may be used to test the sensor at various temperature levels to evaluate the possibility of a shifted (incorrectly calibrated) sensor. A shifted sensor could result in poor driveability complaints. Refer to Temperature Versus Resistance . |
| • | After the engine is started, the ECT sensor should rise steadily to about 95°C (203°F) and stabilize when thermostat opens. Verify that the engine is not overheating and has not been subjected to conditions which could create an overheating conditions (i.e., overload, trailer towing, hilly terrain, heavy stop and go traffic, etc.). |
| • | A shorted to voltage sensor signal circuit may cause DTC P0118 to set. |
If the DTC P0118 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 P0118 diagnostic on the scan tool under the Not Ran Since Code Cleared selection in the DTC Information menu. If a DTC P0118 appears in the Not Ran Since Code Cleared list, the P0118 diagnostic has not yet run. When the DTC P0118 does not appear in the Not Ran Since Code Cleared list, the P0118 diagnostic has run. If the MIL is NOT ILLUMINATED and there is no PENDING DTC Status in DTC Information, the P0118 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 ETC sensor circuit. Inspect the wiring harness and components for an intermittent condition. Refer to Intermittent Conditions .
If you cannot duplicate the DTC P0118, 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 in the diagnostic table.
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The Diagnostic System Check-Engine Controls prompts the technician to complete some basic checks and to 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 determines if a fault is present.
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Review the Freeze Frame data in order to determine when the DTC set. Always record this information.
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This step determines if the fault is caused by an open or shorted signal return circuit, an open in the ground circuit or by a malfunctioning ECT sensor.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics | ||||
Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | ||
Is the ECT display at or less than the specified value? | -40°C (-40°F) | Go to Step 4 | Go to Step 3 | |
Is a DTC P0118 set? | -- | Go to Step 4 | Go to Diagnostic Aids | |
Is the ECT display at the specified value? | 165°C (329°F) | Go to Step 6 | Go to Step 5 | |
5 |
Is the ECT display at the specified value? | 165°C (329°F) | Go to Step 7 | Go to Step 8 |
6 | Check for a poor connection at the ECT sensor and repair as necessary. Did you find a problem? | -- | Go to Step 12 | Go to Step 10 |
7 |
Was a repair necessary? | -- | Go to Step 12 | Go to Step 9 |
8 |
Was a repair necessary? | -- | Go to Step 12 | Go to Step 9 |
9 |
Was a repair necessary? | -- | Go to Step 12 | Go to Step 11 |
10 | Replace the ECT sensor. Refer to Engine Coolant Temperature Sensor Replacement . Is the action complete? | -- | Go to Step 12 | -- |
11 | Replace the PCM. Refer to Powertrain Control Module Replacement . Is the replacement complete? | -- | 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 | |
