P0118

DTC P0118

Circuit Description
The engine coolant temperature (ECT) sensor is a variable resistor. The ECT sensor has a signal circuit and a low reference circuit. The ECT sensor measures the temperature of the engine coolant. The engine control module (ECM) supplies 5 volts to the ECT signal circuit and a ground for the ECT low reference circuit. When the ECT sensor is cold, the sensor resistance is high. When the engine coolant temperature increases, the sensor resistance decreases. With high sensor resistance, the ECM detects a high voltage on the ECT signal circuit. With lower sensor resistance, the ECM detects a lower voltage on the ECT signal circuit. If the ECM detects an excessively high ECT signal voltage, indicating a low temperature, this DTC will set.

Condition for Running the DTC
- The battery voltage is between 10-16 volts.
- The ignition switch is ON.

Condition for Setting the DTC
- The ECM detects that the ECT signal voltage more than 4.95 volts.

Action Taken When the DTC Sets
- The ECM illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails.
- The ECM records the operating conditions at the time the diagnostic fails. The ECM stores this information in the Failure Records.
- The ECM uses an ECT substitution of 77 °F (25 °C) when the DTC is set.
- The ECM uses an ECT substitution of -20 °F (-29 °C) for engine starting.
- The ECM uses an ECT substitution of 32 °F (0 °C) for engine running.
- The ECM limits fuel injection quantity within 70%.
- The ECM closes the EGR valve and holds to close position.

Condition for Clearing the DTC
- A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
- Clear the MIL and the DTC with a scan tool.

Diagnostic Aids
- After starting the engine, the ECT should rise steadily to about 176 °F (80 °C) then stabilize when the thermostat opens.
- Use the Temperature vs. Resistance table to test the ECT sensor at various temperature levels to evaluate the possibility of a skewed sensor. A skewed sensor could result in poor driveability concerns. Refer to Temperature vs. Resistance.

If an intermittent condition is suspected, the following may cause an intermittent:
- ECT sensor may have an intermittent open as it heats up.
- Poor connections.
- Misrouted harness.
- Rubbed through wire insulation.
- Broken wire inside the insulation.

Check for the following conditions:
- Poor connection at ECM: Inspect harness connectors for backed-out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection.
- Damaged harness: Inspect the wiring harness for damage. If the harness appears to be OK, observe the "ECT Sensor" display on the scan tool with the engine running while moving connectors and wiring harness related to the sensor. A change in the display will indicate the location of the fault.

Test Description
The number below refers to the step number on the diagnostic table.
5. This step tests for the proper operation of the circuit in the low voltage range. If the fuse in the jumper opens when you perform this test, the signal circuit is shorted to voltage.

DTC P0118

Schematic Reference: Engine Controls Schematics

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