Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Coolant Temperature Sensor (CTS)
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.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.