[AggieZig]

Hi Everyone, posting this in the general forum with hopes it will catch someone's attention who might be able to shed some light.

I'm looking for some help diagnosing a P0456 - Evap leak detected (very small leak) code. This is on a 2010 E91 with the N52 motor.

Initially, I thought I might as well just throw a gas cap at it since it could be a cheap fix. Unfortunately, the code returned.

Today, I tried to smoke test the evap system to see if I could find any obvious leaks. I disconnected the tank vent valve line (under the throttle body) and fed the smoke from there.

- Confirmed the gas cap is not leaking
- No visible leaks from the DMTL, charcoal cannister, or any fittings
- No visible leaks from tank caps where senders/fuel pumps bolt up

However, I did notice a ton of smoking coming out from the dust filter / intake that feeds the DMTL unit. I'm not sure if this should be normally venting or if it should only let air into the DMTL unit.

View post on imgur.com

Is this normal venting? Or is the DMTL unit letting smoke through that it should not be?

I am also noticing a pretty strong gasoline vapor smell while the DMTL pump is running. Could that be indicative of anything?

[mainbearing]

That DMTL pipe looks like plastic, so you cannot just clamp it (it will break). I would think you need to block it and see where the smoke comes out from.

If the pump is running and you smell gas, that is probably where the leak is. Maybe you can place the pump in place of the DMTL and try that. Hopefully smoke will come out where the gas smell did.

[spazzz]

I took off the wheel and removed the filter cartridge.
I had a piece of fuel line hose laying around that fit in the filter housing pipe perfectly.
This is where BMW used to or still does?? recommend. They used to sell a service kit for this.
It will never pressurize the system unless you short the DMTL pump to close otherwise.

[AggieZig]

Originally Posted by mainbearing

That DMTL pipe looks like plastic, so you cannot just clamp it (it will break). I would think you need to block it and see where the smoke comes out from.

If the pump is running and you smell gas, that is probably where the leak is. Maybe you can place the pump in place of the DMTL and try that. Hopefully smoke will come out where the gas smell did.

I'm just wondering why the smoke is venting through the DTML intake pipe instead of through the charcoal canister? If that path is normally open when the DTML isn't running, then wouldn't fuel vapors be able to escape through the same path instead of being forced through the CC?

It looks like the DMTL is designed with a "change over valve" inside and I'm wondering if mine is malfunctioning or stuck open. I do have a replacement DMTL on order, but not totally convinced that will solve the issue.

Agree with you on the gas smell while pump is running. The idea being that if the pump is pressurizing the tank, and I smell gas, it's leaking from somewhere.

[AggieZig]

Originally Posted by spazzz

I took off the wheel and removed the filter cartridge.
I had a piece of fuel line hose laying around that fit in the filter housing pipe perfectly.
This is where BMW used to or still does?? recommend. They used to sell a service kit for this.
It will never pressurize the system unless you short the DMTL pump to close otherwise.

That makes sense. I will try this later today and see if I can spot a leak anywhere.

[335i54n]

you need to electronically close the evap sys to smoke it. i would inpect the senders for cracks, test the purge valve and lastly replace the dtml

[AggieZig]

Originally Posted by 335i54n

you need to electronically close the evap sys to smoke it. i would inpect the senders for cracks, test the purge valve and lastly replace the dtml

Thanks for the tip. How do you close the evap system - is it a matter of jumping pins somewhere or a function in ISTA?

[AggieZig]

Thanks for all the help. I ran the smoke test again with the line connected up to the input for the DMTL motor and was able to pressurize the system. I found the leak, both fuel pump and sending unit caps had cracks that were hidden under the dirt.

[53N30W]

Originally Posted by AggieZig

Thanks for all the help. I ran the smoke test again with the line connected up to the input for the DMTL motor and was able to pressurize the system. I found the leak, both fuel pump and sending unit caps had cracks that were hidden under the dirt.

This is great information as I have been fighting a war with the same thing for a longtime. So many great tidbits on this site, even if you are not having a problem now. Cheers