Is a knock sensor necessary?

How much is a knock sensor?

You are paying an extra $0.20 per gallon for fuel now and can't utilize the extra octane most of the time.

If the light stays on, you should replace the sensor even if the car runs good because when something else fails you will not know until you notice other symptoms like mpg dropping off or misfire, etc.

Maxima's have always had very high strung engines when it comes to maintanence and the type of fuel you use. Let's break this down for you. A knock sensor is one of the many sensors in your car that tell your ecu how the engine is running. It's a phonic sensor that picks up irregular sounds that can be harmful to your engine. Low octane gas in your car will cause your car to knock and can even cause catostrophic engine damage, which I've seen more than once. My first assumption would be that the gas you're putting into your car would cause your engine to detonate(alarm the knock sensor), however, that would bring up several different trouble codes(check engine light). So if your ecu has stored knock sensor codes, I'd go ahead and check them out. Your mechanic may let the car idle and tap on them slightly to see if the engine idle is affected or not. Your car should stumble because tapping a knock sensor is simulating a badnoise(knock or detonation or ping) which will make your ecu go rich or retard timing(make it safe for that period).

yea it controls timing