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 ECT sensor does not reach 113°F (40°C) after a calculated total air flow has been reached.

DTC will set if ECT sensor does not reach 113°F (40°C) after a calculated air flow has been reached and following conditions are met:

• Start-up ECT was between -40°F (-40°C) and 95°F (35°C).
• IAT is greater than 19°F (-7°C).
• Calculated average air flow is greater than 10 gm/s.
• Engine run time is between 30-1200 seconds.
• Distance traveled is greater than .5 miles (distance is only updated when vehicle speed is greater than 25 MPH and calculated air flow is greater than 10 gm/s.).
• DTCs P0105, P0107, P0108, P0112, P0113, P0117, P0118, P0122, P0123, P0130, P0171, P0172, P0201, P0202, P0203, P0204, P0300, P0336, P0440, P0446, P0480, P0481, P0502, P0503, P0602, P1441 and P1621 are not set.

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 failure and store information in freeze frame buffer.