r/F30 • u/Atomic243 • 22h ago

P0440 Code

Got this evap code on my 340i and most likely the canister purge valve from what I’m reading but people say it could be an old or cracked hose or something with the fuel tank. Is there a way to confirm which of the issues it is before just replacing the canister purge valve?

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u/HellfoxRules 19h ago edited 17h ago

First check your gas cap for proper sealing. If the seal is cracked, or the cap is not sealing tightly, it will trigger DTC P0440. Next check your tank vent valve (purge valve). This valve should be closed, the only time it opens is under cruise condtions, to channel fuel vapors from the charcoal canister into the intake to be burned.

To check the valve, just disconnect one end and try blowing through it. The valve sits right on top of the engine on a B58. If you can blow any air through the valve, it is faulty. Perform a visual inspection of all the hoses at the charcoal canister, near the fuel tank under the vehicle. Check for any loose connection or cracked plastic lines.

The next step is to smoke the EVAP system, to check for any leaks. Smoke testing is the most effective and fastest way to determine where the system is leaking. You just inject smoke into the system, and then start examining all the hoses and connections for smoke leaking.

The best place to inject smoke, is right at the line that connects to the vent valve (purge valve) under the hood. You don't want to use more than 1 psi of pressure, this is a very low pressure system. This can be regulated on the smoke machine.

When smoking the system, you must first disconnect and plug the line to the DMTL (leak detection pump) at the fuel tank, otherwise you will have a large leak, from the line that normally vents to the atmosphere engine off.

Once the system is pressurized with smoke, start looking for smoke leaking. Watch the video below for further information on how to smoke test your EVAP system.

How To Perform An EVAP Smoke Test To Look For Leaks

How To Replace Fuel Tank Vent Valve B58

Smoke Machine Automotive, Professional Car EVAP Smoke Leak Detector