Hey omegabenz, where in the world did you hear that!!! Knock sensors and oxides of nitrogen(NOx) have absolutely NOTHING to do with one another. I'd suggest checking your information for accuracy before posting. NOx is an exhaust emission that is controlled by cooling the combustion temperature, usually by the introduction of exhaust gas(EGR). Knock sensors are simply piezo-type vibration sensors mounted to the engine block. Knock sensors can't get "plugged up". Pinging/knocking results from uncontrolled burn of the fuel/air charge. The engine noise that results is the sound of the pistons slapping the cylinder wall. This causes a vibration that's picked up by the knock sensors. The engine/ignition control unit retards the timing until the knocking stops. There are also several other reasons for pinging/knocking. Lean fuel mixture, excessive load, high engine temp and fuel quality can all cause this. Either way, it needs to be taken care of. Phelan, make sure that your transmission is in the correct gear when climbing those "slow, steep hills". If necessary, manually shift to a lower gear, though the transmission should do that automatically. Good luck