Hello All,

I've been dealing with P0456 now and every time I think it's gone the light just comes back on. Initially I thot it was the gas cap, so I replaced it and the light is still on. It seems to be related to the gas tank level, altho I am not sure.

To diagnose, I checked the purge valve in the engine bay and with no power, it holds suction. I additionally checked the hose that goes from the valve to the rear of the truck and it also holds vacuum.

The line that comes from the fuel tank, when I disconnect it and blow or vacuum air thru it, it allows me to and doesn't hold pressure or vac at all. I'm not sure if that's how it's supposed to be?

Any insight would be greatly appreciated

Thanks,
Pete

 

what model year as it may use either a leak detection pump or esim; completely different evap designs so they must be diagnosed differently.

 

2008 Ram 1500 5.7L

 

it uses an esim
it takes approx. 1 week times for the monitor to run to completion...hence why the light reappears so infrequently.
proper diagnosis requires a scan tool and evap leak detector/smoke machine.
-when the truck starts and the purge is commanded open...the system draws vacuum and this vacuum closes the esim switch. you would need a scan tool to view the switch closing. if you shut off the engine and open the gas cap...the switch should now open. this confirms the switch is working.
-with a evap tester...you pressurize the evap system and watch the flow meter. if the flow meter drops to zero...there is no leak....replace the esim. if there is a leak...you must trace the smoke with a black light.

without these tools...and having replaced the gas cap....I would replace the esim as it is the most common part to fail. Its relatively cheap. It must be orientated the correct way as it uses gravity to move a valve. I would also replace the esim filter. this filter must be free from restrictions or the fuel tank will be hard to fill and could collapse due to high vacuum in the tank. the filter also protects the esim from dirty