P0118

Diagnostic Chart:

Schematic:

The engine coolant temperature (ECT) sensor is a thermistor that varies resistance according to changes in engine coolant temperature. The ECM supplies a five-volt reference through a pull-up resistor(s) to the sensor, which is connected to ground. When the sensor is cold it has high resistance (high signal voltage at ECM). As the sensor temperature increases, its resistance decreases (lower signal voltage at ECM). The ECM uses the signal voltage to determine engine coolant temperature. DTC P0118 sets when the ECT sensor signal voltage at the ECM is below the calibrated voltage value (over the calibrated temperature value).

DTC PARAMETERS
DTC P0118 will set if ECT temperature is below -39°C (-38°F) when:
^ Condition exists for longer than 2 seconds
^ Ignition is On

DTC P0118 diagnostic runs continuously with ignition On.

P0118 is a type B DTC.

DIAGNOSTIC AIDS
To locate an intermittent problem, use Scan tool to monitor ECT temperature with ignition On, engine Off. Wiggling wires while watching for a change in ECT temperature may locate the area where a short to ground in the wiring may exist.

An intermittent open in ECT sensor can set this DTC. Run engine after it has cooled down and monitor ECT on Scan tool. The temperature should rise smoothly to 88°C (190°F) as the thermostat opens and stabilizes the temperature of the engine coolant.

The Coolant Temperature gauge will display COLD if DTC P0118 is active.

The ECM will command the cooling fans On if DTC P0118 is active.

The CMP/ECT/IAT/MAF sensors share the same sensor return circuit 2761.

Refer to ECT General Description for a Temperature vs. Resistance chart.

IMPORTANT: A direct short to voltage on circuit 2761 may cause internal damage to the ECM ground trace, or open the sensor element in the ECT and/or IAT sensors.