2005 Taurus, 80K miles, 3.0 Liter, OHV. Check engine light came on and code P0456 “Evap Emission Control system leak very small” Anyone have ideas ? Thanks
I’m going to go out on a limb and suggest you have a small leak in your evaporative emission system 
Cars used to have a vent on the top of the gas tank to allow air (and fumes) to escape when you filled the tank. To reduce pollution, those fumes now go into a charcoal canister. When you drive, some air is sucked through that canister by the engine to combust those fumes. The system is pressurized, and your computer is detecting a small drop in pressure. It could be many things, but the most common is that your gas cap is not seated quite right. Did the light come on right after you added gas to the tank? Take off the gas cap and carefully reclose it.
Other reasons for this code could be a defective gas cap that doesn’t hold pressure any more, or a small leak in the charcoal canister or the tubing and valves that connect the tank to the engine. It may be some trouble to track down, but your car won’t pass an emissions test until it’s fixed. On the plus side, it’s not a safety issue and you can continue to drive while you work on the problem.
Start by taking off the gas cap and reclosing it carefully. If it was the cap, the light will go out by itself after 3-4 driving cycles. If that doesn’t help, try a new gas cap. After that, you’ll need to find a mechanic.