EVAP System Vent Problems – Gas Won’t Go Into Tank

2:30 pm Check Engine Light, DIY, EVAP, How To Auto Repair

The black specs in the picture are charcoal pellets that came from the charcoal canister.

© DenLorsTools.com Summary: DenLors auto repair blog covering a common EVAP (Evaporative Emission Control) system problem. EVAP charcoal canisters can contaminate the system causing flow and vent issues. Sometimes problems with venting can make it almost impossible to fill up at the gas pump. A very frustrating ordeal at the pump is to have the pump shut-off while putting gas in BEFORE the tank is full. Some vehicles even have the fuel splash back out due to improper vent tube operation. This car repair article points out several things to look for when charcoal from an EVAP canister has broken loose and has entered the EVAP lines causing a blockage.

EVAP system faults are a leading cause of CEL’s (Check Engine Lights) to come on, i.e. Low Purge Flow (Code P0497). Out of all of the EVAP system faults, LEAKS are the most common cause of problems. For repair tips and advice on EVAP system leaks see our previous car repair article on Common EVAP Codes  which covers pinpointing EVAP system leaks. This automotive repair article today covers another problem with EVAP systems, which are  flow and vent issues caused by the EVAP canisters coming apart. When filling up at the gas pump, many people can’t resist squeezing an extra .50 or .75 cents after the pump initially shuts off. Little do they know that overfilling the fuel tank could cost them a lot of time and trouble in the long run. When putting too much gas in the tank, fuel can end up where it shouldn’t be… in the charcoal canister. Inside the charcoal canister, there are tiny pellets of charcoal. The normal function of the EVAP charcoal canister is to temporarily store gasoline FUMES (not liquid gasoline) that evaporate within the fuel supply system (mainly from the fuel tank). When car owners overfill the fuel tank, the EVAP charcoal canister can be saturated with raw fuel instead of just fumes as it was designed. The liquid fuel can float the pellets of  charcoal out of the canister and into the EVAP hoses. If pellets enter solenoids or orifices, they can be plugged and restrict the proper flow of vapors within the system. The fuel tank needs to breathe. Anything causing a restriction will prevent it from breathing properly reducing efficiency and sometimes causing early shutoff at the gas pump during fill-up.

Hyundai Elantra charcoal canister is located at the left rear of car.

Easy Check of an EVAP Canister
One easy way to look for a problem with the charcoal canister is to remove the EVAP hoses that attach to it. Sometimes the pellets will fall out of the hoses revealing the problem. Any solenoids in close proximity of the released pellets will more than likely be affected. Hoses will need to be blown out with compressed air. By blowing air through the hoses, venting can be checked. Make sure not to blow too much pressure into the tank since a leak from the fuel pump seal or from some other component could be created. If the tank is not venting properly it may actually swell when blowing air in through the hoses. It may be normal for the tank to expand a little and quickly contract when the air exits the tank. Feel and squeeze rubber hoses to check for orifices. The Hyundai Elantra in the picture had a plastic orifice which acted as a filter, capturing some of the pellets and preventing them from traveling further into the EVAP system. The canister and the purge solenoid was replaced and the orifice was cleaned and re-installed. The venting was restored to normal. The customer was advised NOT to overfill the tank in the future to prevent the same problem from re-occurring.

No Charcoal Pellets Found in Hoses

If experiencing “early pump shut-off” and there are no charcoal pellets found in the hoses there could be a problem in the fill neck itself or from a built in valve in the tank. Sometimes the problem can be pinpointed to a  check ball sticking or a vent valve not opening properly. It’s always a good idea to check the service repair manual for specific vehicle information. Frequently there’s a known issue which is called out in a TSB (Technical Service Bulletin). Other times if a TSB is not put out by the manufacturer, a dealer tech may be able to help identify common problems with certain makes and models. If the tips laid out in this auto repair article did not help lead to the problem with your car, check out our other articles.

Related Car Repair Blogs and Auto Tools

OTC3108 OTC OTC3108 Pocket Scan Code Reader

EVAP Smoke Machine Tech Article – How to check for leaks

Common EVAP Codes – Car Tools, Tips & Advice

OBD II Scan Tools and Code Readers – DenLors Tools

18 Responses
  1. dennisb - Auto Tool Sales :

    Date: December 26, 2010 @ 9:06 am

    Our most popular OTC Smoke Machine (Detector for checking EVAP and vacuum leaks) is the Leak Tamer 6521. See the link below for the product listing on our the main part of our car tool website. There’s a video on the product listing showing it being used.
    otc 6521 leak tamer plus evap smoke machine
    OTC 6521 Leak Tamer Plus Evap

  2. Tyrone :

    Date: January 15, 2011 @ 12:38 am

    nice one

  3. peejoe :

    Date: August 26, 2013 @ 2:23 pm

    I have a 2008 Dakota 4×4 v8. Seems like it only takes 10- 15 dollors of gas at a time and the pump clicks off. This will happen over and over till I stop putting gas in. I also have a P0452 code now and then.

  4. dennisb - Auto Tool Sales :

    Date: August 26, 2013 @ 2:55 pm

    Could be something restricted. The P0452 means “Fuel Tank Pressure Sensor Circuit Voltage Low”. May or may not be related to the filling issue. I would explore a little like mentioned in the article. Good Luck.

  5. peejoe :

    Date: September 18, 2013 @ 11:44 am

    I also have a 2008 Dakota 4.7 4X4 and I can only get 5 bucks of gas in and the pump shuts off … and I also get a p0452 the odd time …. but the fuel fill problem is consistant and a pain in the u know what …

  6. dennisb - Auto Tool Sales :

    Date: September 18, 2013 @ 12:23 pm

    Wow sounds like it gotten worse since the last time you commented. Be sure to let us know what you find out. Good Luck.

  7. Joe37 :

    Date: March 19, 2014 @ 11:01 am

    Will it pass smog with this problem?

  8. dennisb - Auto Tool Sales :

    Date: March 19, 2014 @ 11:09 am

    If there’s no check engine light on, meaning no codes are stored, I don’t see why it would fail. Good Luck.

  9. Aar Bee :

    Date: May 26, 2014 @ 11:36 pm

    Thanks a lot for this post. This was exactly the problem with my car.

  10. dennisb - Auto Tool Sales :

    Date: May 27, 2014 @ 7:41 am

    Glad the article helped. Keep us in mind for future purchases of automotive tools.

  11. tlcraig215 :

    Date: June 29, 2014 @ 11:27 am

    This seems to be the problem with my 04 Elantra. After “topping off” my tank the engine would stall at normal operating temperature. I unplugged the EVAP sensor near the intake and the problem went away. I then cleaned out the charcoal canister which was mostly filled with liquid gas and let it evaporate for a couple hours. After reinstalling everything the car still stalls. My question is will leaving the EVAP solenoid unplugged, located near the intake, cause any other damage (I.e.wearing out the O2 sensor) until I can replace the canister and sensor?

  12. dennisb - Auto Tool Sales :

    Date: June 29, 2014 @ 12:11 pm

    The purpose of the EVAP system is to recirculate the fumes rather than letting them vent into the atmosphere. I wouldn’t expect any drivability issues or ill effect on any sensors including the Oxygen sensors. However you’ll have a CEL (Check Engine Light) on and the car won’t pass any type of inspection. Fuel economy would suffer some also.

  13. Jay :

    Date: July 23, 2014 @ 4:01 pm

    My 2000 mustang gt it’s throwing code and the gas pump clicks, what could it be?

  14. dennisb - Auto Tool Sales :

    Date: July 24, 2014 @ 7:11 am

    Jay, could be clogged vapor hoses leading back to the vapor canister or faulty valves. It will take some testing to determine the issue. Good Luck.

  15. day :

    Date: March 9, 2015 @ 12:57 pm

    I have a 1988 camaro and i can put about $.30 in before gas starts coming back out of my filler neck! What is my problem need a quick fix, I ran out of gas 2 times yesterday trying to get home!

  16. dennisb - Auto Tool Sales :

    Date: March 9, 2015 @ 3:30 pm

    Hve to do some checking. Sometimes, you can turn the filler nozzle upside down to get it to take gas on some models. Good Luck.

  17. Lizzie :

    Date: March 26, 2015 @ 6:43 pm

    I was in a minor rearend accident with my Hyundai Sonata. Before the accident when I filled up my tank the display would read 320 miles til empty/ 23 mpg. Now after fill up the display reads 280 miles til empty/ 18.9 mpg. What could be causing this? The bodyshop said I had no gas tank damage.

  18. dennisb - Auto Tool Sales :

    Date: March 27, 2015 @ 7:25 am

    Lizzie, the computer calculates your MPG (Miles Per Gallon) constantly with the latest data. This information, MPG x Gallons in the tank, is used to calculate the estimate of DTE (Distance to Empty). This is just an estimate, but usually a pretty good one. FYI, don’t trust this completely because there is some margin for error, if the fuel gauge is slightly off. The Carmax I worked at had a customer who had their vehicle which wouldn’t start, towed in with a dash reading saying 20 miles to empty. Turns out, the car was actually out of fuel. On your vehicle, for some reason the estimated MPG’s went down after your accident. If nothing else has changed, like; 1. The type of driving, like more city driving. Or different driving habits which formed after the accident. 2. A running issue, like a misfire, which could have made the engine light come on. 3. A low tire from a leak which would increase rolling resistance etc.

    If none of the above could be the cause, I would suspect a misalignment of the rear wheels caused from the accident. This could cause increased rolling resistance causing the MPG to go down. It would also cause excessive tire wear over time. Just a slightly bent suspension part can throw the alignment out of whack. It may be necessary to have the car hooked up to the alignment machine because sometimes even for a professional, it’s hard to notice a problem with the naked eye. Good Luck.

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