Circuit Description
The engine coolant temperature (ECT) sensor is a thermistor mounted in the engine coolant stream. The Powertrain Control Module (PCM) applies a voltage (about 5.0 volts) through a pull up resistor to the ECT signal circuit. When the engine coolant is cold, the sensor (thermistor) resistance is high, therefore the PCM will measure a high signal voltage. As the engine coolant warms, the sensor resistance becomes less, and the ECT signal voltage measured at the PCM drops. With a fully warmed up engine, the ECT signal voltage should measure about 1.5 to 2.0 volts.
Conditions for Running the DTC
The engine is running.
Conditions for Setting the DTC
| • | The ECT sensor signal indicates an engine coolant temperature less than -39°C (-37°F). |
| • | The above conditions are present for more than 25 seconds. |
Action Taken When the DTC Sets
| • | The PCM will illuminate the malfunction indicator lamp (MIL) during the second consecutive trip in which the diagnostic test has been run and failed. |
| • | The PCM will store conditions which were present when the DTC set as Freeze Frame/Failure Records data. |
Conditions for Clearing the MIL/DTC
| • | The PCM will turn OFF the malfunction indicator lamp (MIL) during the third consecutive trip in which the diagnostic has run and passed. |
| • | The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction. |
| • | The DTC can be cleared by using a scan tool. |
Diagnostic Aids
Inspect for the following conditions:
| • | Poor connection at the PCM--Inspect harness connectors for: |
| • | Backed out terminals |
| • | Improper mating |
| • | Broken locks |
| • | Improperly formed or damaged terminals |
| • | Poor terminal to wire connection |
| • | Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems. |
| • | Damaged 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. Refer to Wiring Repairs in Wiring Systems. |
If DTC P0118 cannot be duplicated, the information included in the Failure Records data can be useful in determining vehicle mileage since the DTC was last set. If it is determined that the DTC occurs intermittently, performing the DTC P1115 Engine Coolant Temperature (ECT) Sensor Circuit Intermittent High Voltage diagnostic may isolate the cause of the fault.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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Verifies that the fault is present.
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If DTC P0118 can be repeated only by duplicating the Fail Records conditions. Refer to Temperature vs Resistance table. The table may be used to test the ECT sensor at various temperatures to evaluate the possibility of a shifted sensor that may be shorted above or below a certain temperature. If this is the case, replace the ECT sensor. Refer to ECT Sensor Replacement. If the ECT sensor appears to be OK, the fault is intermittent. Refer to Diagnostic Aids.
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This vehicle is equipped with a PCM which utilizes an electrically erasable programmable read only memory (EEPROM). When the PCM is being replaced, the new PCM must be programmed. Refer to PCM Replacement/Programming.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | ||
Does the scan tool indicate the ECT parameter is less than the specified value? | -38°C (-36°F) | |||
Does scan tool indicate DTC P0118 failed this ignition? | -- | Go to Diagnostic Aids | ||
4 | Test the signal circuit of the ECT sensor for a short to voltage. Refer to Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | ||
5 |
Does the scan tool indicate the ECT parameter is more than the specified value? | 139°C (282°F) | ||
6 |
Does the scan tool indicate the ECT parameter is more than the specified value? | 139°C (282°F) | ||
7 | Inspect for faulty connections at the ECT sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | ||
8 | Test the ground circuit of the ECT sensor for an open. Refer to Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | ||
9 | Test the signal circuit of the ECT sensor for an open. Refer to Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | ||
10 | Inspect for a faulty ground or signal circuit connections at the PCM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | ||
11 | Replace the ECT sensor. Refer to Engine Coolant Temperature Sensor Replacement . Did you complete the replacement? | -- | -- | |
|
Important: : The replacement PCM must be programmed. Replace the PCM. Refer to Powertrain Control Module Replacement/Programming . Did you complete the replacement? | -- | -- | ||
13 |
Does the DTC reset? | -- | System OK |
