The evap canister is a trap for gasoline vapor and it constantly keeps the system under a vacuum (managed from the intake manifold and the valve marked MOT) to keep the tank and associated parts under a vacuum.

The system self checks itself by closing off a valve on the charcoal canister and engine vacuum is applied to the system - if the pressure sensor does not register negative pressure in given time it will set the error code for it.

In usual cases overfilling (topping off) fuel or pouring some additive without a funnel in the filler throat causes the evap canister to flood with gasoline or the additive you were trying to pour in.

This is very bad and can cause permanent damage to the canister or the valve on top of it.

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2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)