charcoal EVAP canister question

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Hi all: This is a two part question for the board... I get a slight odor of gas after driving my 95 Maxima and parking it in the garage. I've had it to the dealer that I use from time to time and they did (I think) a pretty thorough inspection. They were not able to find any obvious leaks and their only suspicion is the charcoal canister needs to be replaced. This is an expensive part for this car and although I could attempt installation myself, I may elect to have them do it in which case that is more $$. I always thought evap systems were "closed". If there are no leaks in the lines, where is the odor coming from? Is there some over pressurization vent or something that opens up? Also, the gap fine is fine and holding pressure. Now to the second question...some folks on a Nissan board I frequent suggested checking for engine codes with a scanner. They said that just because the CEL is not on does not guarantee there is not a code to be retrieved. Is this correct? From what I understand Nissan has their own scanner (I think it is called Consult). Should I take it to another dealer to see if they can retrieve any codes that might point to something other than the canister? What about an OBDII scanner? I don't have one nor have ever used one but see they are really cheap at PepBoys and the like. Does anyone know if an OBDII scanner would retrieve the same codes as what Nissan might determine? If so, can I get away with one of these $14 USD ones I see for sale or should I invest in something a bit better and what should I look for as a first time buyer/user of one of these.
 
Double-check the hoses going to the canister; a cracked/split hose is usually the culprit- not the canister.
 
IIRC, in general 95 model year is not OBD-II compliant. I am not sure if Nissan started their compliant in 95. You can probably ask the Nissan forum about that. If it is NOT OBD-II compliant, then there is NO OBD-II reader/scanner can read the code. I know GM uses ALDL connector on the 95 model year which has a different pin and different standard, it is their version of OBD-I (one instead of two).
 
IIRC, in general 95 model year is not OBD-II compliant. I am not sure if Nissan started their compliant in 95. You can probably ask the Nissan forum about that. If it is NOT OBD-II compliant, then there is NO OBD-II reader/scanner can read the code. I know GM uses ALDL connector on the 95 model year which has a different pin and different standard, it is their version of OBD-I (one instead of two). At that time, each manufacturer have different standard and only their reader/scanner can read the code. Plus the code is manufacturer specific since there is no standard.
 
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First things first, you stated that you 1995 Nissan Maxima..., OBD2 was not required by federal law until 1996. So the first thing you need to verify is which diagnostic system your vehicle has. OBD2, among other things, standardized the DLC connector to the trapezoidal connector you commonly see on any current scanner, prior to that each auto manufacturer had their own connector and interface. So first you before you buy ANYTHING verify which diagnostic system you car has. Secondly, assuming your car has OBD1, you will not be able to use an OBD2 scanner, and since OBD1 is less robust you might not even get a code for an EVAP issue. I suggest you get a good service manual and start troubleshooting from there. Just because you have a certain code does't mean you should start replacing parts willy nilley. Find the root cause of the issue first. When does the gasoline smell start, right after you fill the tank completely, 3/4 or when the fuel gauge is nearly at empty? It could quite possibly be the purge solenoid is not working, or a cracked line. Replacing the charcoal canister in that situation will do absolutely zero except make your wallet lighter. Replacing parts based on DTC's is the worst thing you can do. DTC point you to the issue, further diagnostics are still needed. Here is an example: lets say you go get gas some early morning on the way to work, you pay for your gas, and are happily on you merry way to work that 9-5, all of a sudden in traffic your amber check engine light goes on, so you go to autozone where they do free scans and the the scanner shows an EVAP code. You read that it is a something to do with the EVAP canister so you go and spend xxx amount of cash and replace the canister, the check engine light is still on and goes back on after being cleared, your like [censored], so you do more diagnostics, and check you fuel cap, which was not properly closed and bang it dawns on you the gross leak was from an improperly closed fuel cap which would have been a free "repair". Now this is an exaggerated example but I have seen it happen. Moral of the story is first find out which on board diagnostic system you have, find out exactly which components are affected or involved in the DTC, check ALL components to verify that they are in working order and finally replace the faulty component based on a complete diagnosis. Google and YouTube are you friends and are free. Use them. Hope this helps
 
Hi: Folks on the Nissan board state the car is actually OBDII compliant. I have seen folks at the emission station occasionally hook up to a connector under the dash on the passenger side which I believe is the OBDII connector.
 
There is a connector in my 95 Suburban also under the dash but it was not OBD-II compliant. You can try going to the part store and see if it is really compliant. Unfortunately, we cannot determine that for you.
 
Originally Posted By: JMJNet
IIRC, in general 95 model year is not OBD-II compliant.
Yeah 95 was a strange year of transition to OBD2. Lots of Japanese 95s have an OBD style connector but don't run the OBD protocol and thus don't work with OBD scanners. On the Max it might be a simple matter of grounding a test pin to make the CEL flash the code out- might not need a scanner at all? NissanMaxima, Check for a rusted or broken vapor line along the bottom of the vehicle, right from the tank to the canister. You'd really notice it on warm days or just after fueling up.
 
Instead of trusting what folks on the Maxima forum say (which can vary depending on the build date of your car or the submodel) verify it by looking for the compliance sticker ON THE VEHICLE itself. You can usually find the info on the door sticker that has the VIN and manufacturer info. Just google obd2 compliance sticker and go to images, you will find the location of the stickers.
 
That Maxima uses a primitive EVAP system compared to most post-2000 cars with on-board refueling vapor recovery and returnless fuel systems which are a bit more air-tight than the 1st gen systems. I'd start first by checking the lines between the vacuum switching valve for both EGR and EVAP and the vapor lines between the intake manifold, carbon canister and fuel tank. There's also a valve at the tank as well. Your car can't run a check pump to check for an EVAP leak or loose fuel cap but there's a rollover/vent valve at the tank to route vapors to the canister.
 
Get under the car and inspect the hoses to/from the canister. I've changed one out. On my Toyota, there is a tricky fuel line connection you just had to be patient with. THhe canister for your maxima is only $55 on rockauto. Canister for my Rav4 goes for $350 but I found one on ebay for $250.
 
If needed, consider rebuilding your canister. I could never pay hundreds of $$$s for 4 bucks worth of charcoal pellets and 3 bucks worth of plastic.
 
Check for gas leaks underneath or any oil leaks if dropping on exhaust etc.. check the hoses (as mentionned) and check for exhaust leaks. If its none of the above, I wouldnt worry about it. My 07 smells like gas when started too.. I wouldnt bother spending the money on an EVAP canister even if it was the culprit. Just not worth it. Park the car outside if worried about Carbon Monoxide. I wouldnt worry too much though about a "slight odour of gas".
 
Does your car go "whoosh" when you open the gas cap to buy gas? It should, as it's supposed to keep a slight vacuum so the fumes stay in. I would go to an emissions guy and get the car smoke tested. You could have a hole in the top of the gas tank for example. Even if the car were (partly) OBD-II compliant as an experiment on Nissan's part, the EVAP testing system might not have been included as it was expensive.
 
I use to get an occasional smell of gas after driving but with no obvious leaks and no other symptoms. It turned out to be a leak at the fuel filler hose between the filler neck and the tank. It only leaked when in motion and would dry quickly when stopped. Why do you think that the evap canister is the issue?
 
Originally Posted By: NissanMaxima
Hi all: This is a two part question for the board... I get a slight odor of gas after driving my 95 Maxima and parking it in the garage. I've had it to the dealer that I use from time to time and they did (I think) a pretty thorough inspection. They were not able to find any obvious leaks and their only suspicion is the charcoal canister needs to be replaced. This is an expensive part for this car and although I could attempt installation myself, I may elect to have them do it in which case that is more $$. I always thought evap systems were "closed". If there are no leaks in the lines, where is the odor coming from? Is there some over pressurization vent or something that opens up? Also, the gap fine is fine and holding pressure. Now to the second question...some folks on a Nissan board I frequent suggested checking for engine codes with a scanner. They said that just because the CEL is not on does not guarantee there is not a code to be retrieved. Is this correct? From what I understand Nissan has their own scanner (I think it is called Consult). Should I take it to another dealer to see if they can retrieve any codes that might point to something other than the canister? What about an OBDII scanner? I don't have one nor have ever used one but see they are really cheap at PepBoys and the like. Does anyone know if an OBDII scanner would retrieve the same codes as what Nissan might determine? If so, can I get away with one of these $14 USD ones I see for sale or should I invest in something a bit better and what should I look for as a first time buyer/user of one of these.
If a code is stored on the ECU/PCM it will just be evap system code, it won't help you at all. OBD2 systems are closed fuel vapor systems, except for the one way check valve type gas cap that allows air into the tank as fuel is used to displace the space the fuel once occupied. Thats why a lose fuel cap will trip a CEL. The fuel tank and evap system is under pressure. That's just a statement, nothing for you to ponder! Please just move on to this next paragraph.... I have had a few vehicles with damaged evap systems from collisions, I owned a collision repair shop. I tried a few times to repair them, or find the problem. I spent far too many hours with "NO" results! I found a mobile diagnostic specialist and he had a smoke machine that he would pressurize the evap system with, and it would show plan as day exactly where the leak was. Your literally wasting your time trying to find it on your own, unless your extremely lucky. Good luck! Find a guy with a smoke machine!
 
The valve in the gas cap does not act in normal operation, it is to prevent damage to the tank from excessive pressure or vacuum if there is a problem with the EVAP system. Ordinarily, as the gasoline is consumed, air enters the tank through the canister and vapor line to the pressure control valve near the tank. As someone else noted, you should almost always have a pressure or vacuum in the tank when taking the cap off.
 
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Hi all Lots of great information I'm thankful for and will need to digest and explore. I've learned a lot in the past 24 hours so here is what I've determined plus answers to some questions: 1. I found a picture of an OBDII connector at http://www.obdii.com/connector.html that matches what I have. However, I read elsewhere that this is still not a guarantee it is truly OBDII or fully OBDII compliant and to check the sticker under the hood. I did so and no statement on the sticker about OBDII compliant. 2. I actually have the factory service manual which I bought shortly after I bought the car new. I looked through it and under the Engine Control chapter it talks about the ability to use a "generic scan tool" or "OBDII scan tool" that complies with SAE J1978. I looked up that SAE number and it appears that was the standard when OBDII first evolved. 3. I searched threads on the Maxima forum and folks are convinced the 95 is OBDII compliant apparently evidenced by their ability to read codes with OBDII scanners. 4. All evidence points to the fact that is OBDII complaint but perhaps not fully compliant? 5. Removing gas cap does indeed result in "whoosh" of pressure when fueling up and I had the gas cap check too. It is fine. 6. My cursory examination of the lines, gas tank, etc. shows no cracked lines, etc. Nissan had it up on the lift but I'll crawl around some more and examine further. 7. Rust issues like hole in gas tank not likely as the car is super clean and rust-free So, from the comments, it appears a scanner might not even be helpful. I think I should check if there is a specific code for the EVAP canister. Perhaps this is buried in my 500 odd page FSM! The suggestions about smoke testing are interesting. What type of shops offer that? Emission repair places? So, are there any actual vents on this car or cars in general that would result in the gas odor or must it be coming from a leak? I don't spot any on the diagrams in the FSM. Finally, someone asked why I think it is the EVAP canister. This is the conclusion of the Master tech at the Nissan dealer who seems quite knowledgeable. I don't know what other tests they did though other than visual examination hence my initial inquiry here about maybe buying an inexpensive OBDII scanner. I may indeed end up living with it. It isn't awful - just an annoyance, but I would like it fixed if possible and reasonable.
 
You can go to AutoZone and ask them to scan it. One time I had bad Fuel Injector orings and could smell gas.
 
"The suggestions about smoke testing are interesting. What type of shops offer that? Emission repair places?" That would be the best place to check.
 
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