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 ECT decreases, ECT sensor resistance increases. As ECT increases, ECT sensor resistance decreases. PCM monitors voltage input from ECT sensor and converts it into a temperature value. DTC will set when:

• ECT is less than 20°F (-6.7°C) at start up, and ECT sensor value is 95°F (35°C) or less after engine has been running for greater than 20 minutes.
• ECT is 20-50°F (-6.7 to 10°C) at start up, and ECT sensor value is 95°F (35°C) or less after engine has been running for 5 minutes or greater.
• ECT is greater than 50°F (10°C) at start up, and ECT sensor value is 95°F (35°C) or less after engine has been running for 2 minutes or greater.

When DTC sets, MIL will illuminate after 2 consecutive ignition cycles in which diagnostic runs with active fault. PCM will record operating conditions at time of diagnostic failure and store information in freeze frame buffer.