Second Hose from Valve Cover (Not PCV) What is it?

Attached is the engine bay of a 2005 Camry. In red is the area of the PCV valve with a hose that goes directly into the intake manifold. What is the purpose of the second hose circled in blue? What is it called and what is it’s purpose. Is this also part of the PCV system? It goes into the hose from the air box, after the mass air flow sensor, after the air box, before the throttle body valve and before the intake manifold. Here’s another picture with the beauty cover removed.

I believe this is called the breather valve? But what exactly is it’s purpose and how is it different then the PCV valve?

where is this going . . . ?!

is the hose split?

do you want to know how to replace it?

The PCV system on your vehicle works where the PCV valve opens to allow crankcases gases into the valve cover, and those gases along with those under the valve cover are pulled back into the intake to be re-burned.


@db4690 So it has this path. Yes it’s split. I’m not trying to replace it, just now what purpose it serves.

Air box -> Mass air flow sensor -> split 1 -> throttle body valve -> intake manifold

Breather valve -> split 1 -> throttle body valve -> intake manifold

PCV valve -> intake manifold

@Tester - isn’t what you described the PCV valve? What’s the purpose of the breather valve circled in blue?

It’s a bulk hose, correct?

Go to your local parts store with the part and tell them you need breather hose. They’ll match up the diameter and cut you off the length you need


I don’t want to replace it, I’m just wondering what purpose does it serve? Why is there a need for a PCV valve and a breather valve on the valve cover?

I’m not sure what you mean by bulk hose

This makes no sense at all . If you are not going to fix it why even care what it does. Bulk hose , long rolls of different size hoses on a reel that are cut to the length the customer needs.

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@VOLVO_V70 I’m trying to increase my knowledge. I understand the purpose and the point of the PCV valve. But what’s the purpose of the breather valve? There are two valves connected to the valve cover, they do different things? PCV valve allows oil gas mixture out to reduce pressure. The breather valve let’s clean air in for what purpose? Why do we need clean air going into the crank case outside of the clean air going into the combustion Chambers via the intake manifold for the intake valves.


That is a “Breather” hose or “Make-up air” hose, no valve in that hose.
Fresh air is let into the engine so that a vacuum does not develop inside the crankcase and to provide “Positive Crankcase Ventilation”. The breather hose also provides a path for the blow by gasses to escape the crankcase when there isn’t enough manifold vacuum for the gasses to be drawn though the PCV valve.

Thanks so do more blowby gases go through the PCV valve or the Breather side?

there isn’t enough manifold vacuum for the gasses to be drawn though the PCV valve.

When does this occur?

When there is high manifold vacuum, at idle for example all of the blow-by gas goes though the PCV valve plus some fresh air.

When the throttle is wide open there is no vacuum for the PCV system and the blow-by gas increases, the blow-by gas escapes though the breather hose.

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Wow this is interesting. I can see that the math could get complicated fast.

I never “floor it” or am in the wide open state, I presume gases go through the breather side in some low vacum states other than fully open? Like half open for example? If greater than half open gases go through breather?

Yea I’m not sure there’s a answer but I see that the math can get complicated quick.

At half throttle there can be as little as 5 to 10 inches of vacuum, not enough to draw all of the blow-by gas from the crankcase.

The PCV system just ain’t that complicated unless you let the nomenclature overwhelm observation and logic.

Yes the breather line works both ways it provides"filtered" make-up air when the PVC valve is open and provides venting of blow-by gasses during periods of low vacuum IE full throttle. It vents the gasses into the intake past the mass airflow sensor so they don’t foul the sensor. However that means if there is a leak in that hose it will likely cause the engine to run lean and set a code or at least jack up the long term injector trim. Exactly when the air is flowing either direction depends on how much blow by the engine has at different temperatures and various stages of wear over it life.

I probably should have added the condition of the air filter can make a big difference in the breather flow:)

So i should have an oil catch can on the breather side as well, sense blowby gases can get exhausted on that side to?

Why not, it’s your car so you can do what ever you want.

  1. Make sure you use fasteners that won’t rust.
  2. Make sure to use “Locking Wires” aka “Safety wire” on all nuts and bolts
  3. Make sure you add a large magnet to the outside of your oil pan.
  4. You should buy an identical car so you have spare parts.
  5. Make sure your oil filter and drain plug are properly torqued

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A person asks a question, in search of knowledge in general, and they get attacked by the Dogma Police.

If you don’t have something helpful to say, please STFU.


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