Engine Coolant Temperature Sensor Fault
Engine Coolant Temperature Sensor Fault means the computer may be receiving a false coolant-temperature reading It can cause overheating, fan warnings, AC performance problems, or intermittent fan operation depending on the vehicle.
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Most Likely Causes
- 1
Failed fan motor, relay, fuse, or control module
The fan circuit may have a bad motor, stuck relay, blown fuse, or failed solid-state control module.
- 2
Bad coolant temperature or AC pressure input
Fan command often depends on coolant temperature and AC pressure. A bad sensor input can keep the fan off, on, or cycling incorrectly.
- 3
Loose connector, corroded terminal, or damaged wiring
Heat, vibration, road splash, and previous repairs can damage fan wiring and connector terminals.
- 4
Mechanical restriction or debris
Debris, shroud damage, or a seized fan can overload the motor or keep the fan from spinning.
How to Diagnose It
- 1
Command the fan on with a scan tool if supported
Use bi-directional control to see whether the fan responds when commanded independently of engine temperature.
Tool: Bi-directional scan tool
- 2
Check fan fuse, relay, power, and ground
Verify power and ground at the fan or control module while the fan is commanded on.
Tool: Multimeter or test light
- 3
Monitor coolant temperature and AC pressure data
Compare live data to actual engine temperature and AC operation to see whether the computer should be commanding the fan.
Tool: Scan tool
- 4
Inspect fan blades, shroud, connector, and harness
Look for debris, melted connectors, loose pins, corrosion, rubbed wires, or damaged fan blades.
Tool: Flashlight
How to Fix It
Repair confirmed electrical fault
Replace the bad fuse, relay, connector, wiring section, or control module after testing the circuit.
Replace failed fan motor or assembly
If power and ground are present but the fan does not run or runs weakly, replace the fan motor or fan assembly.
Correct sensor or cooling-system input problems
Repair coolant temperature sensor, AC pressure sensor, thermostat, low coolant, or overheating causes that are commanding fan operation incorrectly.
Mistakes to Avoid
- Do not replace the radiator fan before checking fuses, relays, power, and ground.
- Do not ignore fan problems on a vehicle that overheats at idle or in traffic.
- Do not jump fan wires without using proper fused test leads.