Circuit Description
The Engine Coolant Temperature (ECT) sensor is a thermistor mounted in the engine coolant stream. The PCM applies a voltage (about 5.0V) 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 2.0V.
Conditions for Setting the DTC
| • | Engine is running for more than 3 seconds |
| • | The ECT sensor signal indicates an engine coolant temperature less than -38°C (-36°F). |
| • | Above conditions present for longer than 24 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 and Failure Records data. |
Conditions for Clearing the MIL/DTC
| • | The PCM will turn OFF the MIL during the third consecutive trip in which the diagnostic has been 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 the scan tool. |
Diagnostic Aids
Check for the following conditions:
| • | Poor connection at PCM. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection. Refer to Intermittents and Poor Connections Diagnosis Repairing Connector Terminals and Connector Repairs . |
| • | 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 . |
If DTC P0118 cannot be duplicated, the information included in the Fail 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. The Temperature vs Resistance 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. 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.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
1 | Was the Powertrain OBD System Check performed? | -- | ||
Is the Eng. Cool. Temp. below the specified value? | -30°C (-22°F) | |||
Does scan tool indicate DTC P0118 failed? | -- | Go to Diagnostic Aids | ||
4 |
Important: If the 3 amp fuse blows, locate and repair a short to voltage in the ECT sensor wire. Is the Eng. Cool. Temp. at the specified value? | 130°C (266°F) | ||
5 |
Is Eng. Cool. Temp. above the specified value? | 130°C (266°F) | ||
6 | Check for poor connections at the ECT sensor and replace terminals if necessary. Refer to Testing for Continuity , Intermittents and Poor Connections Diagnosis , Repairing Connector Terminals and Connector Repairs . Did any terminals require replacement? | -- | ||
7 |
Was the ECT sensor ground circuit open? | -- | ||
8 |
Was the ECT signal circuit open? | -- | ||
9 | Check for a poor sensor ground or ECT signal circuit terminal connection at the PCM and replace terminals if necessary. Refer to Wiring Repairs . Did any of the terminals need to be replaced? | -- | ||
10 | Replace the ECT sensor. Refer to Engine Coolant Temperature (ECT) Sensor Replacement . Is the action complete? | -- | -- | |
|
Important: Replacement PCM must be programmed. Replace the PCM. Refer to Powertrain Control Module Replacement/Programming . Is the action complete? | -- | -- | ||
12 |
Does scan tool indicate DTC P0118 failed? | -- | System OK |
