On the back of the motor, i have a 2000 Grand Prix GT 3.8 and in the wire harness coming off the O2 sensor in back on rear exhaust manifold, near alternator, there's a plug that nothing is going to it, seems odd to just have a plug there for no reason. If car heats up beyond normal with A/C on and water pump is replaced and thermostat and coolent level is fine, what could be issue?