P0118

Diagnostic Chart:

Schematic:

The Engine Coolant Temperature (ECT) sensor is a thermistor that varies resistance according to changes in engine coolant temperature. The PCM 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 PCM). As the sensor temperature increases, its resistance decreases (lower signal voltage at PCM). The PCM uses the signal voltage to determine engine coolant temperature. DTC P0118 sets when the ECT sensor signal voltage at the PCM is above the calibrated voltage value (below the calibrated temperature value).

DTC PARAMETERS
DTC P0118 will set if ECT sensor temperature is below -39°C (-38°F) when:
^ Condition exists for longer than 6 seconds
^ Engine run time is greater than 1 minute.

DTC P0118 diagnostic runs continuously once the above conditions have been met.

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 an open or short to voltage in the wiring could lie.

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 82°C (180°F) as the thermostat opens and stabilizes the temperature of the engine coolant.

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

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

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

NOTE: A short to B+ on signal circuit 410 may damage the ECT sensor. Check for correct resistance vs. temperature after repair has been made.

IMPORTANT: The PCM uses a different 5 volt pull-up resistor network when ECT reaches 49°C (121°F). Make sure reading is normal below and above this temperature.