Iv been fighting this code for years now. I have replaced all the piping going in and out of the Canister. Replaced the Valve, and replaced the boost sensor.
The code still goes off, seems to go off after driving on the freeway. If I limit myself to short trips no faster than 45 mph the code doesn't go off.

Now for my final try I ordered a new canister, iv removed and tested the existing one and didn't find any problem but its the last part in the system I haven't replaced. Ill get it in two days and am praying its the problem.

I would like to hear from others that had this code and fixed it. What did you do to do to fix it? Id like to see if there are other more rare causes I may have missed, since Iv tested and replaced all the regular ones (Except for the canister).

EDIT:
Thanks everyone who responded.
I have also replaced the gas cap, forgot to mention it.
I have also tested the harness for the purge control valve as per instructions in the dealer manual, and it seems fine as well.

Getting the canister tomorrow, will update with results of replacing canister.

 

is this the code for the Evap control purge valve, solenoid, cansister valve or the canister itself? Cant remember...

The true was to test the EVAP system to the pressure test it and see if it leaks. Then use DTC to test components of the system.

I remember i had the code and replaced the solenoid valve. Blew into every hose and it went away. Check the harness to the valve too as it could need resoldering

 

Don't over look the gas cap.

 

This code is for the solenoid valve plunger that goes into the canister. I will say that the wires could be a short or there is a break in the harness. I would check the ecu out theirs an electrical issue.

 

i had the same code..it ended up being the canister check it...take it off the car and shake it...if theres black **** coming out of it, replace it, its leaking charcoal. if not check gas cap for leaks

 

0903=Canister vent control valve.
valve is stuck,
electrical circuit is bad,
canister leaking charcoal plugging the lines
or jamming up the other valves.

I blew everything out, reconnected all electrical connectors and installed a 3/8" fuel filter in the vacuum line below the master cylinder to keep charcoal at bay until I replace the canister. No code yet in a tank and a half of driving.

 

When I had this problem, changing the valve on the cannister did not fix the problem. What I found was that one of the nipples on one of the small valves on a bracket just forward of the cannister was broken. Could not see it because the short piece of hose held it almost in place. I ended up buying a cannister plus the bracket with the small valves at a JY. Replaced it two years ago - it's been fine ever since. Good luck.

 

Any idea what the small valves are called?

EDIT:
I guess it is the "vacuum cut valve"

 

Although my P0446 was accompanied by P0440 (small evap leak) I fixed both codes by replacing the O-ring which fits between the canister vent valve & the vapor canister, worth a shot... goodluck!

 

There is also a "vacuum cut valve bypass valve" on that same bracket; and the "EVAP purge cut valve" and/or "EVAP pressure sensor" might also be there. Sorry, but it's been a long time since I actually messed with this. All I really remember is that there were a bunch of things connected by little chunks of vacuum hose. Good luck.

 

Any charcoal in any of the lines regarding this code and the EVAP family of codes pretty much points directly to a messed up Cannister, right?

 

Pretty much. If you remove the canister and it starts pouring charcoal bits, time for a replacement. You'll also have to blow out all the lines, and it's not a bad idea to take apart the EVAP valves underhood to clean them out also.

 

^^^exactly what the problem was with mine. blew lines out and replaced canister. have to get all lines/valves clean or else it might not clear/fix the problem. there was a ton of charcoal up at the motor so make sure you get it all out.

 

UPDATE:
I have replaced the canister and while removed blew out the line from the engine to it based on these instructions http://www.aa1car.com/library/evap_n...ntb00-085a.pdf Has a very nice diagram of all the components.

My old one didn't seem to leak any charcoal, so i tried to blow air with the compressor into it and cover the holes with my figures to see if it leaks. It didn't leak and inflated a lil bit and then it started throwing charcoal chunks out. I don't know if that's because i broke it by inflating it or it was already bad

I have been driving a couple of days, no code yet, usually id get the light to go off within a drive or two, for now it didn't even appear as a pending code, but the engine hasn't finished all the tests yet so I'm holding my breath.

Here is a good piece of info I found out while diagnosing this. If you have an OBD meter and the cutoff valve harness is not connected properly the Code goes off instantly (check engine light doesn't turn on but the code is there). Figured this out when i forgot to reconnect the harness. So for anyone having this kind of issue try resetting the ECU with an OBD meter and if the code comes back immediately you have a harness connection issue.

 

This is the hose I put the filter in.

 

Cool, if you know its the canister why not just replace it, its just like $42 on amazon. I dont know why I didnt try replacing it earlier. Also keep in mind 4th gen has two types of canister depending if yours is pre 4/97 or after.

 

Ill replace it when I have a little extra cash. It's not a big priority right now.