Coolant Temperature Sensor (CTS)

The CTS is a thermistor (temperature sensitive resistor) located in an engine coolant passage. The ECM supplies and monitors a 5-volt signal to CTS. This monitored 5-volt signal is then reduced by resistance of the CTS. When coolant temperatures are low, CTS resistance is high, and a high monitored voltage signal is seen by the ECM. When coolant temperatures are high, CTS resistance is low, and a low monitored voltage is seen by the ECM. When fully warmed, CTS should reflect a temperature of at least 185°F (85°C).

Coolant temperature input is used in the control of fuel delivery, ignition timing, idle speed, cooling fan operation, emission control devices and converter clutch application. A CTS which is out of calibration will not set a trouble code but will cause fuel delivery and driveability problems. A coolant sensor circuit problem (open or short to ground) will swing monitored voltage high or low and should set a related trouble code.