72 Engine Cooling System - Temperature Low

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The coolant temperature sensor (CTS) is a thermistor located in a coolant passage on the engine. When coolant temperature is cold the sensor has a high resistance, as temperature increases the resistance of the sensor decrease. The PCM provides a five volt signal to the coolant sensor, which is also connect to PCM ground. The PCM reads the voltage drop on the signal line to determine coolant temperature.

Information Flag Parameters

Information Flag 72 will set if:

  • The coolant temperature is below 0°C (32°F) after the engine has been running for more than five minutes.


  • Information Flag 72 indicates lower than normal coolant temperatures and does not indicate a faulty CTS subsystem.

Possible causes of low coolant temperature

  • Thermostat stuck open
  • Cooling fan always on

NOTICE: Information flags should be used for diagnostic purposes only. They do not necessarily indicate component malfunction/failure.