I have have read all the existing posts at least twice. Not meaning to be flippant.

The light is really slow to come on - an eight count.
I have topped up the overflow tank.
I have replaced the overflow tank sensor.
I have remove and flushed out the overflow tank and yes the floating magnetic ball rattles.
I have replaced the temperature sensor.
The fan runs when the car is warmed up.
The fan runs when the A/C is turned on.
I am assuming the coolant module is in tune with the ECU??????

Any help or suggestion would be greatly appreciated. .

 

It sounds like you've checked everything. The only things I've found that cause this fault are: Faulty Overflow Tank sensor, Faulty Overflow Tank float, Faulty Fan Controller and Blown Fan Controller Fuse. If you've replaced the Overflow Tank Sensor and the Fan runs, then that rules out the Sensor and the Fan fuse. Even though the ball in your overflow tank rattles, it may not float, ie, it could be stuffed (this is a fairly common failure). The fan can also operate while the fan controller is starting to fail, but it usually stops working or ends up blowing the fuse. I'd try a new overflow tank first, then if that doesn't work, replace the fan controller.

 

ARe you really saying that everything is fine except the light comes on just after starting the car? That is:
1) WIth no A/C on and a cold engine, the fan does not run.
2) The fan runs when the engine is getting warm OR when the A/C is on.

If you mean the Fan Control Module, it and the ECU carry on a conversation on the PWM wire running between the two.

In any event, it sounds to me like you have a bad coolant level sensor. But I can't say for sure.

I also offer the attached...

 

I had installed a new coolant level sensor before seeking help.
After turning on the A/C the fan comes on.
When the engine warms up the fan comes on.

TY still looking for input.

 

Ok, so all is well cept the damn light comes on. MOST of the time, that is the coolant level sensor. It can be a flaky fan controller as well.
In fact, the ECU controls that light, if it sees any of this, it will turn the light on:

Indication of low coolant level, either cause it's low or the sensor is bad or the connector to the sensor is bad or the wrong sensor was used.
High engine temperature (the gauge will show it too).
A communications error between ECU and FCM.
Indication from the FCM that fan motor current is out of specs (If the fan is not told to run, then this won't be a thing.)
A flaky FCM.
A flaky ECU. (Not likely, never seen it before.)

SOME of these indications will cause the ECU to inhibit A/C engagement. The fact that you have no such failure is interesting. I do not know if the STAR tool would tell you what the ECU is seeing that makes it want to turn the light on.

 

The coolant light always comes on. Just that it is very, very slow to come on.

 

Check the Fan control module connector for not being fully seated. Had this problem and drove me nuts until I saw the connector was not fully engaged and latched after replacing the water pump.

 

I now the fan control module is in the engine bay, driver's fender. Is there such a thing as a coolant module?