2001, quad cab, 2wd ,Dakota, 3.9L. My engine code is. P0455 (M). that = ‘’Evap Leak Monitor Large Leak Detected A large leak has been detected in the evaporative system.’’ Ok im no mechanic so can anyone please diagnose this terminology for me? Whats the evaporative system and where is it located? Any help at all would be highly appreciated. Thanks…… Tony

 

Basically the computer adds about 6psi of pressure to the fuel tank to see if there are any leaks that are allowing vapors to escape from the system. So, if the computerputs 6psi to your tank and then comes back to check it again,say you leaked 4psi, it only gets a reading of 2psi then you have a large leak in the evap system.

My money is on the gas cap. Go out to the truck and tighten it down until you hear 3 clicks. If that doesn't shut the light off after a little bit of driving then I would have the cap pressure tested to see if it leaks. If it does, then replace the cap and you'll be good.

 

Check the charcoal canister located under the driver side of the cab inside the frame rail for cracked hoses. Mine threw the same code and it was a dried out and cracked U shaped hose on the canister. A piece of heater hose for a replacementand the code went away. Check all the hoses on the evap system starting in the engine compartment and following them to their terminating points, you'll find the leak.

 

Deranged hit it on the head. The gas cap usually triggers the small evap code, while the large evap code is almost always cracked hoses running to and from your gas tank.