What is coolant temp sensor - 2004 Cadillac Deville

cylinder head temp sensor measures the temp of the cylinder head metal itself and the coolant sensor measures the temp of the coolant only. the coolant sensor is mounted in the coolant and the head sensor is mounted only in the metal of the head and not into anything else. check with a dealer.

Bad coolant temp sensor is my main opinion

There are 4 or more. Which do you want to replace? The coolant temp sensor for the dash? The coolant temp sensor for the ECU? The temp sensor for the outside temp reading? The temp sensor for the fans to turn on? Temp sensor for the AC?

On the 4 cylinder motor (2.3L,2.5L), the coolant temp sensor can be located
on the left side rear of the engine, below the cylinder head.

A picture of a typical Coolant Temp Sensor (aka ECT) is below:


Be sure to partially drain coolant below the level of the sensor to avoid spillage when removing the old part. Best of luck on your repair!
Greg

Hello and welcome to FixYa!

If that's the case, I strongly suggest that you replace the coolant temp sensor. Looks like it's faulty and grounding the circuit. The car's computer can detect it that's why it won't start but once you disconnect it, it will for the coolant sensor is bypassed.

Hope this helps and thank you for using FixYa! Have a good one!

coolant temp guage sensor

This is an independant sensor for the temp gauge in the dash.

Sometimes there are two Temp sensors. Did you see if you had two?

the coolant temp sensor is by far the most common fault.the only other thing it could be is the sensor in the coolant header tank.if you disconect the 2 pin sensor from where you top the coolant up and bridge out the 2 pins in the connector with a bit of wire.if this cures the fault you know its the coolant level sensor.if it persists and its straight from a cold start then the coolant temp sensor is the most likley cause.hope this helps.