GM Service Manual Online
For 1990-2009 cars only
ECT Sensor: The scan tool displays -40 to +151°C (-40 to +304°F). The engine coolant temperature (ECT) sensor is mounted in the coolant stream. The engine control module (ECM) applies 5 volts to the ECT sensor circuit. The sensor is a thermistor which changes internal resistance as temperature changes. When the sensor is cold (internal resistance high), the ECM monitors a high signal voltage and interprets it as a cold engine. As the sensor warms (internal resistance decreases), the voltage signal decreases and the ECM interprets the lower voltage as a warm engine.

FC Relay 1 Command: The scan tool displays ON or OFF. This parameter indicates the state of the driver circuit for this device.

FC Relay 2 and 3 Command: The scan tool displays ON or OFF. This parameter indicates the state of the driver circuit for this device.

FC Relay 1 Circuit Status: The scan tool displays OK or Fault. This parameter indicates the status for the state of the driver circuit for this device.

FC Relay 2 and 3 Circuit Status: The scan tool displays OK or Fault. This parameter indicates the status for the state of the driver circuit for these devices.

Ignition 1 Signal: The scan tool displays Voltage. This parameter indicates the status of voltage at the ECM.