How to Test a Coolant Temperature Sensor Without a Multi Meter - No Tools Needed

Here is how to quickly test if an engine coolant temperature sensor ECT has gone bad without a multimeter or any tools.
Many modern vehicle computers have a safety built into the computer that will kick on the coolant fan when it cannot read the coolant temp sensor.
If the coolant temp sensor is not reporting the engine is hot, the computer will think the engine is cool and not kick on the fans.
If the sensor is unplugged, the computer will kick on the fans since it has a fault mode or safety built-in.
If the computer does not have a fault mode, often the two wires going to the sensor can be jumpered, which will report to the computer that the engine is hot, and the computer will kick on the coolant fan.

It is best to get a wiring diagram of the vehicle's coolant temp sensor before any test.
By using this information user assumes all risk of use.

[bigaparker]

You just don't know i been on this truck for days and this worked. Thing is the temp sensor is new. Must be bad from the factory.

[Eurospec]

I’m having a similar issue with my current coolant temperature fan sensor. It’s a 4 pin. It also controls the AC cut off switch. The thing is when I turn the car off after normal driving the fan does not come on. The fan only comes on while driving. Would that mean it’s a faulty sensor or could I be getting under 12 Volts?

[Mattscalf]

So my coolant temperature sensor plug broke and I had to replace it but I forgot to take a picture of which wire was on the top and bottom(or right or left depending on the sensor is placed) doesn’t matter which wire (mine being a blue with a yellow line and a brown wire) goes where. Thanks

[dang]

Just to be clear if the fans never come on but then do with the jump wire test this proves the sensor is bad? Thanks for the video

[hamidoucissokho]

I unplugged mine but the fan still didn’t go on

[SoulRadio.]

I unplugged my sensor in the car immediately started to get hot??!