According to Haynes Manual, 2001 and later 2.3L Ford Ranger, the
Cylinder Head Temperature (CHT) sensor replaces the Engine Coolant
Temperature (ECT) sensor on earlier models. The CHT sensor is
located between the #2 and #3 spark plugs in the cylinder head and
can be accessed through the valve cover. Carefully pull back the
CHT cover to expose the electrical connector then disconnect it
from the CHT sensor. Unscrew the CHT sensor and remove it.
Installation is the reverse of removal, being careful not to
overtighten the CHT sensor when installing it.