This post describes one of the diagnosis steps for the P0446 code on a 1999 Nissan Altima. Specifically the testing and replacement of the canister vent / purge solenoid valve. This applies to all second generation Nissan Altimas which are 1998, 1999, 2000, 2001.
For more information on what this valve is or the function of the evaporative emissions system see my post about the P0446 Evaporative System Canister Vent Control Valve Circuit.
The canister vent / purge solenoid valve is located just behind the passenger side rear tire, next to the gas tank. You can locate it by looking for the charcoal canister which is a large, black square box on the drivers side of the gas tank. The solenoid valve is attached to the front end of the canister.
In order to test the solenoid valve it needs to be removed and tested with an external 12V source.
1. Remove the 2 10mm bolts that mount the solenoid valve to the canister housing.
2. Separate the solenoid valve from the canister by pulling the valve straight out, towards the front of the car. It is held snugly by an o-ring.
3. Disconnect the vent hose from the solenoid valve. There are no claps/clips, just slide/twist it off.
4. Disconnect the electric connector from the solenoid valve by pushing the green release inward. I found it easier to do this last so that I could manipulate the valve as needed and use a screwdriver to push on the green release.
1. Attach an alligator clip to each of the two leads of the solenoid valve you just removed. Warning: Be sure the metal portion of the alligator clips are not touching each other! This will create a short when you connect it to the battery and fry/spark/melt your wires and/or damage your solenoid!
2. Attach one alligator clip to the positive terminal of your car battery and the other to the negative terminal of the battery. It doesn't matter which goes to which.
3. You should hear and feel the solenoid energize and close the valve. If this doesn't happen, check and make sure the clips are applied correctly. If it still doesn't happen it's likely that your solenoid valve is malfunctioning. If it does happen, clean one of the hose connections and try blowing through the valve. If you can feel or hear any air going through then the valve is not closing completely and needs to be replaced as well. See the video below of a valve that doesn't work. See the video in the replacement section for an example of a working valve.
I found the exact-fit OEM replacement made by Dorman through Advance Auto Parts. Part number 911-501. You can then do some internet bargain shopping to find it cheaper. I was able to find it on Amazon for half of the price: Dorman 911-501 OE Solutions Vapor Canister Purge Valve.
Hopefully this write-up was helpful. Please feel free to comment about successes, or suggestions for improvements!