Coolant Temperature Sensor (CTS)

WARNING: This page does not describe the selected car, but rather 10 other vehicles, including the 1994 GMC Yukon, 1994 GMC Suburban, 1994 GMC Pickup, 1994 GMC Cab & Chassis, and 1994 GMC C3500 HD. However, it is still accessible from the selected car via links, so may be relevant.

The CTS is a thermistor (temperature sensitive resistor) located in an engine coolant passage. The PCM supplies and monitors a 5-volt signal to CTS. This monitored 5-volt signal is then modified by resistance of the CTS. When coolant temperatures are low, CTS resistance is high and the PCM sees a high monitored voltage signal. When coolant temperatures are high, CTS resistance is low and the PCM sees a low monitored voltage. 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, emission control devices and converter clutch application. A CTS which is out of calibration will not set a trouble code, but can cause fuel delivery and driveability problems. A coolant sensor circuit problem should set a related trouble code.