2002 GMC Sierra 4.3L P0446 P0443

I have a 2000 GMC 3/4 ton that had the same code come up. At first I thought it was a faulty vent valve solenoid (per GM bulletin), but when I took it out and electrically tested it, it worked fine. The problem with GMC trucks is that the "filter" in the vent valve is very coarse and lets all kind of dust pass right through it and right into into the charcoal filter canister. I finally took out the canister and because of the tight fits, that job was no fun. After removing the canister, I discovered it was full of an amazing amount of dust and I couldn't blow through it. Rather than buy a new canister, I worked quite a long time shaking and blowing all the dust out until I could blow through it freely. Getting the canister back in was even worse than taking it out, but now the thing works perfectly and I no longer get the P0446 even on a nearly empty tank and it didn't cost me a dime. By overfilling the tank you may have plugged up the canister with fuel or you may be full of dust like mine (depending how dusty it is where you drive). Take the canister out and see if you can blow through it. If it is plugged, and you can't clean it out, you may have to buy a new unit (~$100). You may have noticed that after resetting the code you can drive for months without getting a check engine light if you keep the tank filled up more than 3/4 at all times. That's because the vent valve test doesn't run until your tank is lower than 3/4 full. Hope this helps. BTW, keep the code reader (assuming that's what you really have) because it is so nice to know what's wrong when that cussed light goes on. I'd never be without my reader. Wish I would have spent the extra money and bought a real scanner so that I could perform tests and read more detailed data.

Thanks "Old Geezer", I live in an apartment complex so working on my truck is not allowed. I have seen on the web several different bulletins that are supposed to fix the problem. They both seem to address the filtering problems of the vent. It's a real fine line talking to the service advisor about things you have seen on the web because they are the "trained experts". The part about not setting the code if you keep your tank filled 3/4 or more was very interesting, that's exactly what I do. I call it my 1/4 used rule, by the time I use up 1/4 tank gas has hopefully gone down and I fill it back up. That explains why it takes so long for the code to set again, now to explain this to the dealer "trained experts" without getting into WW III because you heard it on the web, "hey that guy is not a dealer mechanic, what does he know"! It looks like I have to get taken to the bank for a new canister, troubleshooting and new vent and filter, PLUS LABOR! Hey I am on a restricted set income and this repair job sounds like it could cost me upwards of $500! Ouch! God gives and the dealer takes.

Hi Sierra 2002. Don't let the "professional" mechanics snow you. You are the customer, you have the money they want and if you don't like their attitude, you can go somewhere else. IMO, you should let them know up front that that's exactly what you are going to do. Good advice from people that have "been there and done that" is valid, even if that advice is off the net and your mechanic will just have get used to that. If you have to, print out the advice and show it to them then have them tell you why it is such bad advice after all. If they won't discuss it, don't argue with them, just go somewhere else where the guys aren't so closed minded and let them know why you are going. Remember, you are the "boss" and they are the "hired hands" no matter how important they think they are. That's my advice if you have to go to these guys (which I don't for the most part). Regarding your work space: The job is actually pretty easy once the truck is on jack stands and you can crawl under it. It doesn't require any special tools either. If you have a indoor garage attached to your apartment, you can shut the door and nobody will be the wiser. If you don't, is there a parking lot you can use on a Sunday? If you started in the morning, you could have the parts out, cleaned (or replaced) and everything put back together by the afternoon. I will warn you, you will have to take out the drive line, but that is very easy and only requires the removal of four bolts at the differential end. Let me know if you need any detailed advice.

Old Geezer I am going to need further help. Taking out the drive shaft? PM me or I'll PM you with my email address.

It's super easy. Just take out the four bolts at the far end of the shaft, push the shaft forward until it clears the U-joint retainer cups, carefully slide it out of the transmission while supporting its forward end and lay it on the ground. That's it. When you go to put it back in, try to put it in as it came out. You may have to rotate the U-joint retaining cups at the differential very slightly to line up the four bolts. Be sure you tighten them properly without overtorquing them. The hard part is taking the three hoses off the charcoal canister and then getting the damned thing out. It is a very tight fit down there. You will have to pry a lot, so be sure to jack up the truck so you have room to work. By the way, get one of those LED head lamps because they work wonders for seeing what you are doing down there - much better than any trouble light. Getting the canister back in is no fun either and you may have to shave off the extra plastic around its edges like I did.

Dealer service departments run the gamut from outstanding to incompetent rip off mills. They can change from the former to the latter really fast, too. If nothing else I would get a second opinion. Have you though about seeking out a private shop? There are many out there that specialize in GM that dealerships actually send cars to that they can't figure out. I used to work for one.

I ran across a helpful post on http://www.chevroletforum.com/_77352/tm.htm It had the bulletins, procedure, and pictures for the latest "FIX". #02-06-04-037D date Apr 16 2008. This was the most recent info I could find on P0446! Oh I forgot, you can't click on the link I typed. You have to go to chevroletforum >> Chevy trucks,Vans&SUV's>>Sliverado>> Check engine light is on To get to it, if you just click on the link I thought would take you there it says "Page has been moved or unavailable", or something like the. I just rechecked it for accuracy.

Well, that link didn't work for me, but no problem. Anyway, if you don't want to crawl under the truck and get yourself dirty or if you are unlike me and are not really handy or confident working on cars, I would strongly suggest you ask around and try to find an honest independent mechanic (almost an oxymoron these days). I would strictly avoid the dealer, but that's just me. The problem you have is simple and straight forward and there are actually few things that could be wrong to give you this code. It is not rocket science or anything specific to GMC products so any good mechanic (or even an amateur mechanic like me) can do the job. Talk to a prospective mechanic first and see if he tries to snow you with all kinds of technical terms and suggests work he is "just sure" you will need to have done. At the very most you will will require a new charcoal filter (<$100 because a mechanic will not try to salvage it) or a vent valve (~$50). Throw in about 3 hours labor and that's all it should cost you. Keep in mind that if you do the job yourself you may be able to salvage the filter and the valve and (like me) it will cost you nothing except time and dirty hands/clothes.

Old Geezer I hate it when puters don't behave. Again go to www.chevroletforum.com/ once there scroll down to the section titled Chevy Trucks, Van & SUV's. There you should find a vehicle "Silverado", click on it and the "Check engine light is on" should be the 10th topic down. Last post 9/19/2008 6:27:30 AM by ChrisRod. I worked on this a lot navagate to it you will see what I have been trying for you to see.

OK, I read through the topic you linked to and I'd like to tell you that replacing ONLY the vent valve is NOT sufficient . Dust goes right through those valves and ends up in the canister and if you don't clean out or replace the canister the problem will come back again. I know because the first time I only cleaned out the vent valve and the problem returned. After the code appeared once again, it dawned on me that the canister would certainly have dust in it too and I was right -- only I had no idea what a huge amount of dust I'd find. I shook over a full cup of dust out of the canister and had to whack and whack it while blowing through it to get it unplugged. I believe that the internet price of a new canister was ~$80 and for $80 I can do a lot of blowing and whacking. In the end the canister passed gas perfectly and the unit has been working perfectly and passing the tests for about a year and a half now. If yours is plugged with old gasoline, you may be able to put carburetor cleaner through it and get it working again or you may have to buy a new one. Here's what I'd suggest you do (if you want to do it yourself): Crawl under the truck (left side near the gas tank) and with the canister still in the truck, take off the large hose going to the vent valve and also one of the small hoses. Put a rubber hose on the fitting where the small hose went and try to blow through it. You should be able to easily blow or suck through it. If you suck on it, be very careful because you might have raw gas in there. If your breath does not flow easily or not at all, you have probably have a plugged canister. Next blow on the large hose you removed previously. With the power off, your breath should pass easily both ways. If you can't get it to pass air, your vent valve is plugged and you can either try to take it apart and clean it out (like I did) or buy a new one. By the way, it is unlikely you have a electrical problem with that vent valve because if it was failing to close (it's normally open and only closes when under test), you would get other failures beside 446. By shopping on-line for all the parts (I like Rock Auto), you can buy new everything for a fraction of what the dealer will charge you for just one part and you can save all those labor charges too. As I said, it is not a hard job to do and it doesn't require any special tools, but you will need a place to work, you will have to jack the truck up, you will have to crawl and work under it and it will take you 2-3 hours depending on how much time you spend fooling with the canister. One other thing, if you have a check engine light showing, you will have to reset it and your tank will have to be less than 3/4 full for the test to run. Well, I think I've about beaten this horse to death. Let me know if you plan to do the work yourself and if so, how it turns out for you.

Old Geezer I crawled under my 2002 GMC Sierra plain jane 4.3L Vortec to get an idea of what my weekend was going to look like. My canister if I am not mistaken looks to be mounted at a right angle to the frame. It looks like the hardest part is going to unhook the tubing, the canister should just drop down after the bracket bolt is taken out. However the vent valve solenoid is mounted in a very tight spot where it's going to be really fun to unhook the line and unplug it. I am deeply greatful to you for your indepth responces and patience with me. I look forward to what this weekend brings. I have printed out the entire post on this subject and will be thinking of you when I am having all my fun this weekend, I just hope I don't choke on charcoal and gas sludge! I will report back with what I find, once again THANK YOU!

OK, good for you for doing it your self. Your description of where it is and its orientation is exactly right. I sure hope you are right about removing it because mine was a whole lot more difficult. Here's what I suggest you do. DO NOT remove the vent valve . The place it is located is a bitch to get to. You can test if it is plugged from where it is by blowing on the large tube you remove from the canister. I would be very surprised if your vent valve was plugged. If it is plugged, you may be able to clear it by blowing long and hard on that tube and forcing the dust out, but again, I think it is unlikely that it is plugged. If it is not plugged, it is highly likely your canister is plugged and you will have to remove it. In fact, even if your vent valve is plugged, your canister probably is too and it will have to be cleaned or replaced anyway. When I went to clean out my canister, I had to whack it dozens of time with a rubber mallet to loosen up all the caked dust in the thing. I held it so the large hole was down while I whacked it and you wouldn't believe the amount of dust that came out of it. If your canister is plugged with old gasoline gunk, you may have to spray a whole can of carb cleaner through it, catch the solvent and pour it through again and again until you open up the filter. That or just buy a new canister. Now, I have the 6 liter engine and the 3/4 ton chassis and perhaps my canister is in a tighter place. I had to slide the thing toward the center of the vehicle to get it out of its housing. To make it the last couple of inches, I had to take off the drive line. I sincerely hope yours is easier and you are able to remove it (and replace it) without all the prying, along with the loud and long cussing I had to do to get mine out (and back in again). With any luck, they improved the design between 2000 and 2002. Actually, as said before, taking off (and putting back) the drive line is the easiest part of the job. By the way, getting the hoses off is no fun. Get some things to pry with before you start. The hoses have some kind of cheesy plastic locking devices that you are supposed to hold in, but holding them in really doesn't work and you will probably end up just prying them off. Get your pry tool under a hose end and carefully pry while avoiding bending it too much and breaking something. After you are done, I think it would be instructive for you to describe what you did, what you found, what you had to replace and how well it worked after you got done, so let us know.

Old Geezer, I was at my local Harbor Freight store and picked up a 6Pc. "Fuel Line & A/C Quick Disconnect Tool" item number 97576. Maybe you can check out the item I am talking about at the stores website. They look like they might make unhooking the lines pretty easy. I'll try to post an image if I have the rights to do so.

Hello Sierra. How did the job turn out? Were you able to put your finger on the problem and fix it or did you have to take it to a shop?

Old Geezer: It has been rather cold and rainy here but sometime this week I will take it to my godmothers garage and start on it. I DO have the Actron CP9180 Scanner, thought it would be a good tool to have in my arsenal. I'll post back what I find. I don't believe you can control the vent/valve with the scanner. This is whats referd to as bi-directional communication. If you know better feel free to PM on how to best use this scanner against this problem.

Old Geezer: Sorry for not posting. My daughter has just moved back in with me and my whole world has been turned upside down. It maybe a long time before I can actually work on it but I WILL post my results. The Fall brings cold temps and working on it is risky, don't want to crack a plastic line. The other day when I was at the dealer talking about this problem some women brought in a U shaped piece of plastic line. It look like it was from an Evap. System from the way it looked, $110 !

I have to admit that I'm a little disappointed because I am really curious to see if what I've suggested is really what is wrong with your Evap. system, but I understand. You are probably right to avoid working on it in the cold. Not much fun crawling around on the cold ground. The problem doesn't really effect the drive-ability of the truck and it won't affect the gas mileage, but worrying about that MIL coming on all the time can drive a guy nuts. Of course, if you reset it and keep the tank full, it won't come on. You can even pass most State's pollution checks if you only have that test pending - I know you can here in Calif. and we have pretty strict laws. Anyway, doing it yourself can be fun and it's fun and profitable to save the money, but doing it without a heated and well lit garage can also be very uncomfortable and time consuming. You might consider just taking it to a shop. It shouldn't cost you a whole lot more than $300 or so to get it fixed. Personally it would drive me crazy, but if you don't mind the hassle of the MIL coming on and then resetting it every so often, you can live with this problem until you sell the truck or you take it in for some serious mechanical work years from now. Anyway, good luck with whatever you decide to do.