01 SC2 Coolant Light Comes on 15 sec after start
 

Have a 2001 SC2, she just passed 195k. Coolant light comes on about 15 seconds after engine start, and stays on, no blinking. I replaced the coolant overflow tank with a new one, as the old one looked like OEM, the connector at the bottom looks clean. Didn't help. Then replaced the temp sensor on the driver side of the engine. Didn't help, but that sensor was VERY old. Then replaced the sensor on the air intake. Didn't help. Any other sensors anywhere that could be having that light come on? I checked all fuses, all working.

Any thoughts?

Thanks in advance.
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I'm thinking the signal from the sensor at the bottom of the reservoir is not making it to the ECM which also means the ECM is transferring who knows what to the BCM which controls the idiot light.

You should be able to confirm this by connecting a scanner to the OBD2 port and reading real-time data for that sensor variable, which I believe is either open or closed. I have no idea what the name of the parameter is. It's possible it may be a manufacturer's code since it does not set the service engine soon light.

In addition to the above, I would trace the wiring from the reservoir pigtail all the way to the ECM. You may be able to find a wiring diagram to tell you which color wires they are and where they go into the ECM terminal wise.

I don't know if it would be on a fused circuit since it is presumably just a closure contact. Circuit is continuous or not.

What mix of water and coolant are you using?

Hello?