Circuit Description

Intake Air Temperature (IAT) sensor is a thermistor (resistance changes as ambient temperature changes) in series with a fixed resistor within PCM. PCM supplies a 5-volt reference voltage to IAT sensor. As temperature changes, IAT sensor resistance changes, which changes voltage.

As intake air temperature decreases, IAT sensor resistance increases. As intake air temperature increases, IAT sensor resistance decreases. PCM monitors voltage input from IAT 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 failure and information in freeze frame buffer. PCM will enter Fail-Safe Function and assume intake air temperature is 68°F (20°C).