Hyundai Repair: engine light on, hyundai sonata 2002, engine vacuum

Question
As I saw a question dated 9/5/2006 about the same kind of car and problems I am wondering if I give you more details you can help me.
The car is Hyundai Sonata 2002, 4 cyls. Present mileage 150000Km (94000 miles).
I had the engine light on first time at 125000KM. Code P0446 Evap sys - vent control. No problem found and it was cleared at the dealer service shop. Next I had similar problems with the fuel gage. Did not go to F. I went to dealer, run few tests and they said could not find the problems, likely something wrong in the wiring.
After that the gage returns to normal.
Yesterday at 150000Km the engine light came on again and with the same cod. The shop result; clear code and ran test with scanner, no leaks or faults can be found.
Seams that these problems are similar and could be design or manufacturer issues. Can you help me with some ideas, what I can do?


Answer
P0446 means that your evap system is retaining vacuum when it isn't intended to.  Running an evap self-test with the scanner won't cause this code to set, ever, so passing the self-test at the dealer doesn't particularly mean anything.  I've seen a multitude of problems cause the P0446 code:

- malfunctioning fuel tank pressure sensor fooling ECM into thinking there's vacuum in the fuel tank when there is none.
- stuck open purge control solenoid valve applying engine vacuum to tank whenever the engine is running.
- liquid fuel in vapor lines isolating fuel tank pressure sensor from actual fuel tank conditions
- clogged canister (usually caused by fuel in canister-- this is often intermittent)
- canister close valve stuck shut (also typically intermittent)
- canister filter clogged

If the shop can duplicate the vacuum condition in the tank, they should be able to isolate the problem.  In fact, there's a technical service bulletin about diagnosing it (although it leaves out the faulty tank pressure sensor possibility).  You can view the TSB at www.hmaservice.com.  You'll need to register for a free account, and the site requires Internet Explorer.  Since you're not in the U.S., some things may not apply, but if you're setting a P0446 code, this TSB should.  Look for TSB 04-30-001.

For the fuel gauge, if you're having trouble actually getting the fuel in the tank, then you should expect that you actually have a problem with the system venting, probably from one of the last three problems listed above.  If, on the other hand, if the tank fills but the gauge doesn't read full, then you probably have an issue with the fuel level sender in the tank.