Another consequence of P1865 engine overheating may be a blown head gasket. Heat makes aluminum swell almost three times faster than cast iron. Thermal stress can distort the head and make it swell in areas that are hottest like those between exhaust valves in adjoining cylinders, and areas that have restricted coolant flow like the narrow area that separates the cylinders. The typical aluminum head swells most in the middle, which can crush the head gasket if the head gets too hot. This will usually cause the head gasket to leak compression between adjacent cylinders, or leak coolant into the cylinders.
I will actually answer your question. The specifics on this particular code are at the link.....http://p1865.enginediagnosticcode.com/2001- jeep-grand-cherokee
Search Jeep Grand Cherokee Questions
Jeep Grand Cherokee Experts