Nissan Repair: 96 nissan max emisssons test failed, advanced auto parts, sensor circuit

Question
egr flow failed,knock sensor 1 circuit(bank 1 or single sensor(3),and o2 sensor circuit...what the hell is a knock sensor circuit and gas recirculation flow.by the way its funny how they use my computer to tell there computer whats wrong with my car and charger me $27

Answer
simple solution, get a 95.  i think obd2 is too sensitive and causes people to spend too much money at inspection time.  having said that, i really don't have much experience with obd2 motors but according to what your ECU has for stored codes i think you should start with your knock sensor, this could set off the other codes.  unfortunately there is no way to tell if the sensor is bad, its a swap and hope part.  next time go to advanced auto parts or autozone and they will scan your ECU free.  never pay that again, sorry to hear that.  good luck tho, i hope this at least guides you in the right direction.