For 1990-2009 cars

The engine coolant temperature (ECT) sensor is a thermistor that varies resistance according to changes in engine coolant temperature. The powertrain control module (PCM) supplies a 5-volt reference through a pull-up resistor 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 -35°C (-31°F) when:

• | The condition exists for longer than 3 seconds.

• | The engine run time is greater than 4 minutes and 10 seconds.

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

DTC P0118 is a type A DTC.

### Diagnostic Aids

To locate an intermittent problem, use a scan tool to monitor ECT temperature with ignition ON, engine OFF. Wiggling the 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 the ECT sensor can set this DTC. Run engine after it has cooled down and monitor the ECT. The temperature should rise smoothly to 88°C (190°F) as the thermostat opens and stabilizes the temperature of the engine coolant.

The PCM will turn the cooling fan ON if an ECT DTC is active.

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

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

Refer to Engine Controls Component Descriptions for a Temperature versus Resistance chart.