Recurring DTC P0440 and P0325

[TacitBlue]

Ever since I got my 1998 SE last summer, I've been having recurring DTC's. I got an Autel Maxiscan 310 scanner and these were the first two codes I got, P0325 and P1447. I brought it to the dealer and they only got P1447 from their scanner and replaced the Vent Control Valve. About 1 week and 100 miles later the MIL came back on and I got the same two codes again from my Maxiscan 310. Back to the dealer they said the charcoal canister particles had clogged the lines, replaced Purge valve, canister, and blew out the lines. All was well for a couple of weeks and couple hundred miles when the light came back on and I got codes P0325, P0440, and P1448. Brought it to my local repair shop and they replaced a little white circular valve assembly called the vacuum valve. That lasted about a week and the codes P0325 and P0440 came back, I reset it myself, but those same two codes keep coming back after about 1 week. The P0325 is for an engine knock sensor, but since the dealers scanner never got that code (and I imagine their scanner is much more sophisticated than mine) I just ignored that code and figure it's always accompanying some other code like now the P0440. I'm guessing there may be a leak somewhere and the smoke test is my next option, any ideas on this? My main concern is the P0325 code. Is there something wrong with the knock sensor or not? Every now and then I do hear ticking noise at around 2000-2500 rpm, sounds more like a sticking valve lifter though, not an engine knock, are sticky valve lifters an issue, I have only 107,000 miles. Thanks.

[Towncivilian]

Tried replacing your gas cap with an OEM one yet?

[5523Pathfinder]

You should have a evap control valve up on the left strut tower. There is a large rubber hose that attaches and goes back to the evap system. Pull that hosee off and see if any charcoal beads come out. If they do, you need to clean the system by disconnecting as hoses to get the stuff out. The beads are from the charcoal canister in the back. They can get sucked up all the way to the engine and get lodged in the evap system valves and solenoids along the way. Im pretty sure its been posted about before.

[TacitBlue]

I looked in the shop manual and code P0440 is "EVAP Control System, small leak - negative pressure". Would a gas cap leak be on the negative pressure or positive pressure side of the system? Which lines in the EVAP system are under negative pressure? Thanks.

[Towncivilian]

I looked in the shop manual and code P0440 is "EVAP Control System, small leak - negative pressure". Would a gas cap leak be on the negative pressure or positive pressure side of the system? Which lines in the EVAP system are under negative pressure? Thanks.

The FSM claims the gas cap as a potential cause of the code. I'm not sure which side the gas cap is on.

[Alkorahil]

On the 96-2000 pathfinders the charcoal cannister failing and destroying the purge control valve on the cannister is a common problem. You must replace both the cannister and the valve at the same time.