How to Test the Coolant Temperature Sensor/Switch

[Brandybuck]

My temperature gauge reads 230 degrees Fahrenheit. I have discovered that my car is not overheating, however; the mechanic measured the temperature at the thermostat housing with a "point 'n read" digital thermometer to be about 180-190 degrees F. I replaced the CTS a couple weeks ago. The gauge seems to move correctly, beginning below 160 F and moving to 230 F after 10-15 minutes.

Any ideas as to what the problem is? Could the new CTS be malfunctioning just like the old one? Or is the problem the gauge itself? Is there a third device somewhere between the CTS and the dashboard gauge?

I would really like a device that I can plug into the CTS and read a temperature on the device. For example, to isolate the problem, I could unplug the wire from the CTS, and plug in a wire connected to a device I would hold in my hand. If that temperature reads 230 F, then I know for sure that the problem is the CTS. Do I make myself clear? Does such a device exist?

All advice and suggestions would be appreciated.

[Tech II]

Did your mechanic attach a scan tool to see what the CTS was reading in the PCM? Check coolant fan operation? Any codes set?

[ricebike]

I would really like a device that I can plug into the CTS and read a temperature on the device. For example, to isolate the problem, I could unplug the wire from the CTS, and plug in a wire connected to a device I would hold in my hand. If that temperature reads 230 F, then I know for sure that the problem is the CTS. Do I make myself clear? Does such a device exist?

the more expensive OBDII scanners have that function

http://www.youtube.com/watch?v=EyZQw3DGP48 as one of many examples

but, the cheaper scanners will pick up the trouble codes as well if the sensor is bad or the circuit is open from a wire being cut...

http://www.obd-codes.com/p0118

[Brandybuck]

Thanks, guys. I asked a mechanic at the dealership at which I work to use his scan tool on it. He read a 201 F temperature when the gauge said 230 F. I suppose that resolves the issue. The problem must not be with the coolant temperature sensor but with the gauge cluster.

[rkvons]

Originally Posted by Brandybuck

Thanks, guys. I asked a mechanic at the dealership at which I work to use his scan tool on it. He read a 201 F temperature when the gauge said 230 F. I suppose that resolves the issue. The problem must not be with the coolant temperature sensor but with the gauge cluster.

If your car was not overheating before, but started after you changed the temperature sensor, why would you think it is the temperature gauge that has gone bad?

[ricebike]

Originally Posted by rkvons

If your car was not overheating before, but started after you changed the temperature sensor, why would you think it is the temperature gauge that has gone bad?

the OP was having a high reading before and after the sensor change...

but mechanic confirmed that the temps were actually within specs, so his gauge/cluster is the real problem of reading too hot...

[Brandybuck]

Yup, that's the storyline.