Circuit Description

Engine Coolant Temperature (ECT) sensor is a thermistor (resistance changes as engine coolant temperature changes) in series with a fixed resistor within PCM. PCM supplies a 5-volt reference voltage to ECT sensor. As temperature changes, ECT sensor resistance changes, which changes voltage.

As engine coolant temperature decreases, ECT sensor resistance increases. As engine coolant temperature increases, ECT sensor resistance decreases. PCM monitors voltage input from ECT sensor and converts it into a temperature value. DTC will set when temperature value is -40°F (-40°C) for at least .5 second, or 284°F (140°C) for at least .5 second.

When DTC sets, MIL will illuminate. PCM will record operating conditions at time of diagnostic failure and store information in freeze frame buffer. PCM will default to 176°F (80°C).