I have a Lexus 05 ES330, and geting this code P0456, as mentioned in earlier post, I've changed the fuel cap and the light is stilll on. Please, let me know what's the next step to fix this problem.

That's a possible fuse or relay problem unless with the key on your security light is flashing that vehicle may also have an inertia switch (fuel cut off switch ) located usually in trunk near tail lights or behind the carpet on passenger side or passenger footwell area side plastic trim behind that . If equipped. Easiest thing to do is try switching the fuel pump relay with another relay and see if it kicks on.....

The ES330 has a notoriously bad fuel cap problem. Notice that if you tighten the cap two clicks it will come off with one finger. They apparently have a different cap not just a new cap. It will cause the Check Eng light to come on but apparently may also affect the VSC because it affects engine performance. When the VSC light comes on it will also shut down Trac Control and turn on the light. Replace the fuel cap! Cheap first fix. If you need to clear codes when you get the cap at Autozone they'll scan it and clear codes.

code p0456 refers to evaporative emission system--very small leak detected===causes --mechanical fault--hose connections--EVAP pressure sensor.
Mechanical fault could be as simple as the fuel cap is not on tight.

Possible causes - Missing or loose fuel cap
- Incorrect fuel filler cap used
- Fuel filler cap remains open or fails to close
- Foreign matter caught in fuel filler cap
- Evaporative Emission (EVAP) canister or fuel tank leaks
- Evaporative Emission (EVAP) system hose leaking
- Fuel tank leaking
P0456 Chrysler Description The Evaporative emissions system is design to prevent the escape of fuel vapors from the fuel system. Leaks in the system, ca allow vapors to escape into the atmosphere. The leak detection system tests for EVAP system leaks and blockage. During the self-diagnostics, the Powertrain Control Module (PCM) first checks the Leak Detection Pump (LDP) for electrical and mechanical faults. If the first checks pass, the PCM then uses the LDP to seal the vent valve and pump air into the system to pressurize it. If a leak is present, the PCM will continue pumping the LDP to replace the air that leaks out. The PCM determines the size of the leak based on how fast/long it must pump the LDP as it tries to maintain pressure in the system.

you have evap leak first replace your gas cap if it dont work then check for broken line under your car they run from gas tank to engine conparment they all conect to the canaster when you install your gas cap mame sure it clicks over 5 times ok

P0456 DODGE - EVAP System Small Leak
As you see form the list there is not a single problem that causes this code to set.
Possible causes- Missing or loose fuel cap
- Incorrect fuel filler cap used
- Fuel filler cap remains open or fails to close
- Foreign matter caught in fuel filler cap
- EVAP canister or fuel tank leaks
- EVAP system hose leaking
- Fuel tank leaking

Read more: http://engine-codes.com/p0456_dodge.html#ixzz1xQr2MVRf

The most common misfire causes on the cars I've worked on have been:

1. Spark plugs
2. Spark plug wires
3. Ignition coil
4. Fuel injector
5. Wiring to fuel injector
6. Timing Belt
7. Vacuum leak or stuck open EGR
8. Contaminated fuel or bad fuel pump
9. Weak compression
10. Blown head gasket

Article Source: http://EzineArticles.com/1982987

• A small leak in any of the EVAP hoses or fuel tank hoses
• A small leak in the purge valve or vent valve
• The EVAP Canister may be leaking- be sure fuel cap is sealing good, if in doubt replace fuel cap.

P0456 = "Evaporative emission (EVAP) control system leak detected (very small leak)."

Sometimes the light will stay on for 100-500 miles depending on the fault code. You can disconnect the battery to reset it, but you will have to reset the radio and other memory such as seats mirrors.