why is this happening?

98 XJ sport. Auto 4.0L 4X4.
My Aux fan works well with the AC on. But when the temp reaches slightly above 210 on the gauge the fan stops running. And it will not come back on again till the engine is off and cools down below 210. But once it goes over 210 (sitting in traffic) the aux fan will not run.

Could this be a CTS (coolant temp sensor) issue? I unplugged it while the XJ was running and plugged it back in and the fan still didn't work. But it did set off the "check engine" light. Thats to be expected. I know the light is on because I unplugged the CTS while the thing was running. I don't care about that, I care about the fan not coming on above 210. I let it sit and get really hot (225-230 degrees) and the fan still didn't trigger on.

Any ideas?
PS I already replaced the relay today. That didn't do the trick.

If you unplug the CTS while the jeep is running and the fan does not come on, something is wrong in the fan circuit.

If you unplug the CTS while the jeep is running and the fan does not come on, something is wrong in the fan circuit. As a default the fan kicks on when no signal is recieved from the CTS.

I guess I don't understand. The fan does work, except when the engine temp gets hotter then 210.
Where should I check for circuit issues?
or any other issues for that matter.