QuestionI have a manual 6-speed transmission Tiburon. I just returned from a 5 week vacation and I had let my car sit in storage with a virtually empty gas tank to avoid bad gas when I returned. I came home and got my car out yesterday and drove it to the gas station, put in a full tank, and have driven it a pretty good amount in the past 24 hours and then my check engine light came on. Auto Zone gave me the print out with a domestic code of P0449. Can you please tell me how this relates to my car and what it could mean as far as damage and cost? Thank you!
AnswerP0449 indicates that vacuum is accumulating in your fuel tank despite the cansister close valve being closed.
Your car is equipped with a fuel vapor management system and is required by law to monitor it for leakage. Here's how it works:
1. There is a charcoal canister which stores fuel vapors-- charcoal absorbs fuel vapor.
2. The engine control module (ECM) operates a purge control valve to use engine vacuum to suck fuel vapors from the charcoal canister under the desired conditions.
3. The canister has a vent to air so that fresh air can be sucked into the system as fuel is used or the fuel cools.
4. There is an ECM-controlled canister close valve between the canister and the vent to atmosphere.
5. There is a filter between the close valve and the vent to atmosphere to prevent dirt entering the system.
6. There is a pressure sensor which measures vacuum (or pressure) inside the fuel tank.
7. The vehicle tests the system by closing the close valve and cycling the purge valve to apply a vacuum to the fuel tank. The ECM then shuts the purge valve as well and monitors the fuel tank pressure sensor for vacuum loss. If too much vacuum is lost, the system notes a leak.
As mentioned above, P0449 sets if there is a vacuum accumulating in the tank even though the close valve is not closed (i.e. the system isn't yet being tested). This indicates that either the fuel tank pressure sensor is defective (returning too low a voltage for the actual conditions) or that there is a partial or complete blockage preventing the proper amount of fresh air from being sucked into the system. This could be due to the following:
-- plugged canister filter
-- stuck closed close valve
-- kinked or twisted hose/pipe
-- liquid fuel in charcoal canister
-- spider web or similar blockage in vent to atmosphere.
I'll not that if no one has been working on the car between when it was parked and now, that the kinked hose/pipe is particularly unlikely. On the other hand, spiders and other critters like to build nests in things that are stationary for a long time.
How much this will cost will depend on the actual problem and how much time it takes to diagnose. I will say that this can be a particularly difficult problem to diagnose, so you should take the car to a shop with an excellent reputation in driveability/check engine lamp diagnosis. They may have a higher labor rate, but you have a much greater chance that they'll get the diagnosis right the first time rather than take some sort of guess. If you think your local dealer fits this description, take it there. The factory scan tool has the capability of performing diagnostic functions relevant to this repair that other scan tools do not have.
