KrK007

My Check engine light is now on solid, and I stopped by a shade tree mechanic who has the machine to diagnose the codes and told me that I have a medium leak in my evaporative system, which he just said was part of the emissions system and that I'd need to take it to a dealer to fix.

What exactly does this mean, and is it an expensive fix?

The car is running fine.

qldit

Good Morning KrK007, the evap system is generally a fuel tank vapour storage system that allows reuse of vapours one way or another without and venting to atmosphere.
These systems can be quite complex and contain various components that may fail of give odd effects.

It may be worth checking your fuel tank cap sealing ("o" ring) and the valve located in it for operation or replace the tank cap, this can give that kind of error.

Disconnecting the battery for a short period may extinguish the light, but the code will remain stored.

Further to this carefully examine the piping from the tank to the carbon collector and all those connections for integrity.

A service manual for that vehicle should be avaiable from your motor supermarket at relatively cheap cost that will ellucidate on the system operation and componentry.

Others will have different ideas.

Cheers, qldit.

KrK007

The problem may have been the gasoline tank cap. Ironically, someone stole mine and discarded their old cap while my car was parked at work. This meant I bought a new cap for the Neon. Since using this new cap, the Check engine light has not re-lit....

... case of misfortune being good fortune, it seems.

qldit

Good Evening KrK007, yes it would appear that may have most likely been your problem, modern cars can be very fickle, not like the old days.

In view of the problem appearing to have been addressed I suggest we can consider case closed.

Well done there, congrats on light out, thankyou for the feedback.

That code will remain in the computer indefinitely and may be read at some future time so ensure you remember this circumstance.
This does not present a problem, but at some time if those codes are read with a reader you might clear that one from the computer memory, to avoid chasing non existent faults.
Removing battery power for a period simply unlatches the warning lamp indication, it doesn't clear memory.

Cheers, qldit.

KrK007

Well, here it is months later and the problem has returned.

I'm getting Evap system leak - Small (P 0456) now.

Had the code read, cleared, 2 weeks later the Check engine light came back on, same code.

It feels to me like the car seems to be suffering from a power loss too... but that could just be the air-conditioning. Wow it's strong and cold but man it chops 5-7 mpg off my mileage when I use it.... even so though it feels like just recently the car's power and acceleration have dropped off.

Midnight Tech

Set back to "unsolved" status.....

KrK007

Ah, I forgot about this thread. :D It turns out it was the gas cap all along. The light stayed out after the code was cleared and the cap was kept tight. :D

Midnight Tech

Gonna mark this one solved and close it!