Charcoal canisters

Any reason you're checking this?

The usual set-up is three pipes. Two on one end, and one at the other. The two at one end, one will come from the tank (ie the vapour line), and one will go to some form of control valve, then onto the engine inlet manifold. The other pipe is vented to atmosphere (usually runs back to around the filler neck area).

The way it works, is as the tank warms up, the petrol vapour vents from the tank, through the charcoal where the petrol vapour is filtered out by the charcoal, before finally venting from the other end of the charcoal canister. When the engine is then started, the control valve is opened under certain conditions, which causes ait to be drawn back in through the canister vent, where it draws the fuel vapour out of the charcoal, before being drawn into the engine and combusted.

The usual problem is for the vent pipe to become blocked (it's very rare for the actual carbon canister to block), which causes the tank to be sucked in under manifold vacuum.

I don't know why yours has four pipes, or why one goes via the EGR valve.