Up until the late 1980s, most cars had a fairly straightforward throttle control. You stepped on the accelerator pedal, the throttle opened, and air flowed into the engine, where it mixed with gasoline and burned. This burning gas powered the car's wheels, getting you down the road. If you wanted to go faster, all you had to do was step down harder -- the throttle would open wider, giving the car more power.What is the electronic throttle control
Here is what the vapor canister on a Nitro looks like.P0456
A small leak has been detected in the Evaporative Emission System.
What P0456 really means:
The Evaporative Emission System is designed to prevent gasoline vapors from escaping into the atmosphere, and is built around a series of valves, rubber hoses, and a charcoal canister meant to collect vapors as they build up. These vapors are then systematically sent to the engine to be burned off. The computer regularly checks for leaks within this system, either by pumping in air, or by pulling a vacuum, and measuring the time it takes to reach a certain level. When a leak is detected the computer will command the check engine light on and set a P0440, which designates a problem in the system, and another code, such as P0455 0r P0456, to describe the size of leak or other problems in the system..
What causes a P0456 code?
It is good to remember that these leaks are small, in many cases small pinholes about .020”, and you should not worry about gasoline gushing out of the car. With the P0456, these small leaks are commonly seen on older cars, as rubber hoses and gaskets dry out. Most of this emission system sits underneath the car, so it’s exposed to a lot of the grime and wetness of the road during rough weather. Like it or not, these problems are unavoidable, therefore the best approach is to find a good mechanic
What is the severity of a P0456 code?
Minor. These size leaks should not make the car run poorly however, it will need to be resolved before an official emissions test.
What repairs are needed to resolve a P0456 code?
A diagnostic check will be required to identify where the leakage is occurring. Because there is no noticeable change in how the car runs, many people will wait until just before an official emission or smog check. This may not be the best course of action, as this code usually will take some time to diagnose. Plan on dropping the car off for a whole day, and maybe more than one if parts are not readily available.