P0456 This obd code popped up for my smog I've been reading threads about a charcoal canister

Usually this P0456 code is caused by an incorrect or faulty gas cap. Filling the fuel tank with the engine running could conceivable cause this code as well or if the cap wasn't properly tightened. Any of the following could also be the cause:

Read more at: http://www.obd-codes.com/p0456
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From a website:
http://repairpal.com/check-engine-light-with-code-p0456-684

The Check Engine Light may illuminate with five EVAP system related fault codes stored. Our technicians tell us this is generally caused by a faulty EVAP system pump module, which is an integral part of the charcoal canister. A revised canister is available to correct this concern.

this is a code for a small leak in the evaporative emission system. to properly diagnose you will need a smoke machine. but it is usually the vent solenoid on the charcoal canister

What code ? P0442 or P0456 or p0455
DTC EVAP P0442 P0455 P0456
EVAP Leaks P0442 and P0455

Wells EVAP Training with Sgt Tech P0440 P0441 P0442 etc

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

Your best bet is a repair shop with an EVAP
Smoke Machine,to quickly check for leaks.

You won't see or feel anything without smoke
in the system.

P0440 - Evaporative Emission Control System Malfunction

This indicates that a part of the EVAP control system is no longer fuctioning correctly. The EVAP system consists of many parts, including (but not limited to) the gas cap, fuel lines, carbon canister, purge valve, and other hoses. The (EVAP) emission control system prevents the escape of fuel vapors from a vehicle's fuel system. Fuel vapors are routed by hoses to a charcoal canister for storage. Later, when the engine is running a purge control valve opens allowing intake vacuum to siphon the fuel vapors into the engine.

Symptoms: You likely won't notice any drivability problems.

Causes: A code P0440 could mean one or more of the following has happened:
* The gas cap is not installed or working properly
* The purge solenoid has failed
* The canister is plugged and not working properly

Possible Solutions: With a P0440 OBD-II trouble code, diagnosis can be tricky at times. Here are some things to try:
* Remove and reinstall the gas cap, clear the code, and drive for a day and see if the codes come back.
* Inspect the EVAP system for cuts/holes in tubes/hoses
* Inspect for damaged or disconnected hoses around the Evap purge solenoid
* Check and/or replace the sensor
* Check and/or replace the purge valve
* Have a professional use a smoke machine to detect leaks

Other EVAP DTCs: P0440 - P0441 - P0442 - P0443 - P0446 - P0453 - P0455 - P0456

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Here you go
Read all about it
Looks like a fuel vapor leak and a missfire
http://www.obd-codes.com/p0456
http://www.obd-codes.com/p0441
http://www.obd-codes.com/p0303

P0456: Evaporative Emission System Leak Detected (small leak)

Using a Multimeter, check the Evaporative Emission (EVAP) Canister Purge Regulator Valve N80 terminals 1 and 2 for resistance. You should get 22.0 to 30.0 Ohms. If not, replace the canister. If you do, you have other problems.

P0442, P0455 AND P0456 are all evaporative leak monitor test failures (small, medium and large leaks). These codes appear anytime the integrity of the air space above the fuel or the lines to/from the vapor canister or purge valve. If there is no damage to the canister, check the lines that run under the van from the fuel tank and canister to the purge valve (under the hood). Also, check to make sure that the hoses are not split or disconnected where they connect to the purge valve. The P1684 is abit more confusing. This is not a valid DTC for your vehicle. It's possible the scanner the shop you went to is an OTC scanner that is reporting a false code. It's also possible they wrote it down incorrectly. The closest thing that makes any sense is a P1486 which would indicate a pinched hose in the same monitor system as the other 3 codes. Best of luck!