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I brought my Pathfinder to get the emissions test and it failed. Its bringing up trouble codes: P0325 KNOCK SENSOR 1 CIRCUIT (BANK 1 OR SINGLE SENSOR, P0420 CATALYST YSTEM EFFICIENY BELOW THRESHOLD (BANK 1)(5), P0440 EVAPORATIVE EMISSION CONTROL SYSTEM and P0446 EVAPORATIVE EMISSION CONTROL SYSTEM VENT CONTROL CIRCUIT. It has 162,991 miles.  What can be the problem?  

This is a wild guess but I'm thinking it might be your P0325 KNOCK SENSOR 1 CIRCUIT (BANK 1 OR SINGLE SENSOR, P0420 CATALYST YSTEM EFFICIENY BELOW THRESHOLD (BANK 1)(5), P0440 EVAPORATIVE EMISSION CONTROL SYSTEM and P0446 EVAPORATIVE EMISSION CONTROL SYSTEM VENT CONTROL CIRCUIT

again that is just a guess  

That’s a lot of crap, and inherently can be caused by a lot of crap.


Knock sensor circut bank one.  more then likely a bad knock sensor.  
catalyist system below threashold, possible bad cat,
or An oxygen sensor is not reading (functioning) properly
The engine coolant temperature sensor is not working properly
Damaged exhaust manifold / exhaust pipe
Retarded spark timing.

evap emissions control system and vent control circut.  are more then likely related to the comtrol valve.  It might be failing or excessivly dirty. the o-ring might be bad.
Im going out on a limb here, but this might also be causing you cat below threshold code (doubtful though)