What is causing my check engine light to illuminate? (DTCs P0171, P0174, P0325, P1447)?

What's probably causing all of the codes is the P0325 Knock Sensor. The knock sensor needs to be replaced. Replacing the knock sensor will probably clear the other 3 codes.

First you have to see which one actually failed. Most likely the knock sensor needs to be replaced. But it has nothing to do with the other 3. I would replace it & clear the codes & just drive it. Not sure why you mentioned oil leaks, it has nothing to do with those codes as well. You can completely drain the engine oil & drive it & it still will not set those codes.

But unless you know what your doing on the Evap system, I suggest you run it to your local Nissan dealership. That P1447 may cause the oxygen sensors to set as well. You need to see why the O2 sensors are seeing a lean condition. Did you add E85 fuel to your car???? Older cars cannot run off anything that is higher than E10 or 10% Ethanol. If your running 65% or 85% Ethanol, it will set those codes since it doesnt have enough fuel in to. It causes the car to run lean. We run into that badly in Oklahoma with the Cadillacs. If they are not E85, they will set the Check Engine Light on in a heardtbeat if it sees anything higher than E15

Dont get me wrong, the car will run. That isnt the issue. The problem is the O2 Sensors will go crazy cause of the lack of actual fuel & too much alcohol in it causes it to run lean & it will run lean & turn the Check Engine Light on once it sees + or - 10% short or long fuel trim

It doesn't work like that, you have to work through each code to find the cause.

This ALWAYS starts by performing the recommended tests on each sensor that is reporting the problem, this tells you if you have a real problem or a bad sensor.

Because you checked the fluids, especially the oil, and you think you should check it again, tells me you don't understand the trouble codes. They have nothing to do with the oil. The OIL light is concerned with the oil.

I know the 1447 is the purge valve the 171 and 174 is the o2 sensor and then the knock sensor. new 02 new knock sensor and maybe you can get away cleaning and unsticking out the purge valve in rear attach to a black carbon collector box, you can test with a 9voltbattery.

Uh huh.