Circuit Description

ECT sensor is a thermistor (a variable resistor) in series with a fixed resistor in PCM. PCM applies 5 volts to sensor. PCM monitors voltage across ECT sensor and converts it into a temperature reading. When engine is cold, ECT sensor resistance is high. When engine is warm, ECT sensor resistance is low. Therefore, when engine is cold, PCM receives a high voltage input. When engine is warm, PCM receives a low voltage input. DTC P0116 will set when:

Engine coolant temperature is less than 19.4°F (-7°C).
Engine coolant temperature is 95°F (35°C) or less after engine has run for more than 20 minutes.

NOTE: If DTCs P0105, P0110 and P0116 are set together, sensor ground circuit may be at fault.