what is the tcc
Im going to assume the code you have given is PO740 on the obd2 scan tool? PO740 is a TCC circuit malfunction
it is in the transmission
Coolant Recovery Reservoir. There is no sensor in the coolant recovery tank on a 1998 Buick Regal.
take it to a transmission shop. The problem is in the tcc valve body.
Inside the transmission, on the valve body.
Trouble code P1860 means: TCC PWM Solenoid Circuit
yes
Is it located inside of the side transmission pan
Inside the transmission. It can be accessed with removal of the transmission pan.
In the valve body, under the oil pan
Not sure what a TCC (Torque Converter Clutch) sensor is. There is however a TCC relay and a TCC solenoid. The TCC relay is found in the relay/fuse center and the TCC solenoid is located inside the transmission.