What is the purpose of the N112 valve?

**A4 Moda** · 08-22-2009 01:29 AM

according to this picture

The "after simplification" picture on the right side,

the Crankcase breather goes from

Crankcase -- > Atmohsphere

But it's also connected to the N112.

What's the direction of flow here? N112 --> then Crankcase --> then both out the dump (to exhaust or intake)?

I have no freaking clue what the N112 does in this instance.

#2: the Pancake valve (PCV) that works with the crankcase breather hose. What's it's purpose? Does it stay shut under vacuum(idle) ? And open when positive crankcase vapors are exerted on it?

Bottom line: I'm trying to remove, Suction jet pump ONLY, and I'm trying to figure out which way the check valves restrict air, so that I can leave 1 -2 in there for each independent connection.

Thanks

**old guy** · 08-22-2009 04:02 AM

The N112 is the on/off switch for the combi valve. During a cold start the ECU activates the N112 which in turn provides a vacuum signal to the combi valve. The combi valve opens up and lets air into the exhaust as supplied from the SAI pump. If you follow the line from the N112 closely you will see that it is connected to the vacuum canister. the side connection on the line to the vacuum canister is the vacuum source for charging the canister.

What you are calling a pancake valve is actually the crankcase breather pressure regulating valve. It allows regulated air flow in both directions. Under vacuum conditions it allows clean air to enter the block and exit through the PCV Crankcase breather (#13 on the diagram). Under boost conditions it allows air flow out of the block through the TIP connection.

Here is an explanation based on the AWV motor but the AMB functions essentially the same way.

**dougyfresh** · 08-22-2009 05:04 AM

Originally Posted by A4 Moda

according to this picture

Whomever drew that right side chart is incorrect. The line going from the intake manifold to the brake booster should NOT be connected to the crankcase breathing system unless you continue to use the 'suction pump'.

I have a single line going from the IM to a check valve to the brake booster.

Another line from the IM going to the DV and N75.

Then I have a crankcase breather line going from the block to a 'T' joining in with the valve cover. That line then goes to a filtered catch can. There is then a line going from the filtered catch can to my exhaust.

**old guy** · 08-22-2009 05:19 AM

Good morning Doug! If you look real close at the line going to the brake booster you will see that it goes over the breather tube line rather than intersecting with it. The drawing isn't real clear.

**A4 Moda** · 08-22-2009 01:37 PM

Thank you. That was a perfect explanation. Turns out, it was completely my fault. I misread the picture. What I was calling N112 is actually the Crank case breather vent.

I'm trying to remove the suction jet pump from the car. With it's million check valves, i have more than enough leaks to compromise my system.

My question is, if I run one single line between the brake booster and the intake manifold, Which was is the air actually flowing? How will I orient the check valve?

Originally Posted by old guy

The N112 is the on/off switch for the combi valve. During a cold start the ECU activates the N112 which in turn provides a vacuum signal to the combi valve. The combi valve opens up and lets air into the exhaust as supplied from the SAI pump. If you follow the line from the N112 closely you will see that it is connected to the vacuum canister. the side connection on the line to the vacuum canister is the vacuum source for charging the canister.

What you are calling a pancake valve is actually the crankcase breather pressure regulating valve. It allows regulated air flow in both directions. Under vacuum conditions it allows clean air to enter the block and exit through the PCV Crankcase breather (#13 on the diagram). Under boost conditions it allows air flow out of the block through the TIP connection.

Here is an explanation based on the AWV motor but the AMB functions essentially the same way.

**A4 Moda** · 08-22-2009 01:41 PM

Doug,

Under vacuum though, doesn't the engine draw air through the Pancake valve into the crankcase? And then under boost the TIP will suck the crankcase vapors through the breather tube and back through the turbo.

But with your current setup, wouldn't your car be drawing exhaust gases while it's idling?

Originally Posted by dougyfresh

Whomever drew that right side chart is incorrect. The line going from the intake manifold to the brake booster should NOT be connected to the crankcase breathing system unless you continue to use the 'suction pump'.

I have a single line going from the IM to a check valve to the brake booster.

Another line from the IM going to the DV and N75.

Then I have a crankcase breather line going from the block to a 'T' joining in with the valve cover. That line then goes to a filtered catch can. There is then a line going from the filtered catch can to my exhaust.

**old guy** · 08-22-2009 02:02 PM

Originally Posted by A4 Moda

My question is, if I run one single line between the brake booster and the intake manifold, Which was is the air actually flowing? How will I orient the check valve?

You want the flow to go toward the manifold so you can maintain a vacuum in the brake vacuum booster.

**old guy** · 08-22-2009 02:09 PM

Originally Posted by A4 Moda

Doug,

Under vacuum though, doesn't the engine draw air through the Pancake valve into the crankcase? And then under boost the TIP will suck the crankcase vapors through the breather tube and back through the turbo.

But with your current setup, wouldn't your car be drawing exhaust gases while it's idling?

It won't as long as there is no manifold vacuum line connected to the block breather lines. The manifold vacuum is what draws fresh air into the block via the pressure regulating valve.

**dougyfresh** · 08-22-2009 04:25 PM

Originally Posted by old guy

Good morning Doug! If you look real close at the line going to the brake booster you will see that it goes over the breather tube line rather than intersecting with it. The drawing isn't real clear.

Good Evening Fletcher. You are right. It appears that the diagram shows two different lines. My eyes were not open yet. I am sure the original post which contained that diagram specified its not part of the crankcase system but the image alone is kind of misleading pending the users interpretation.

I found out today that even Valeo SMFW OEM replacement clutches can get the stack height wrong

. My friend, who's car it was, was not happy but we came to a good resolution. Why can't manufacturers get anything done correctly?

Originally Posted by A4 Moda

Doug,

Under vacuum though, doesn't the engine draw air through the Pancake valve into the crankcase? And then under boost the TIP will suck the crankcase vapors through the breather tube and back through the turbo.

But with your current setup, wouldn't your car be drawing exhaust gases while it's idling?

I failed to mention that I have a check valve welded onto the downpipe so nothing can go up the lines towards the engine. Only gases can go out of the lines into the exhaust stream of the car.

**[email protected]** · 08-22-2009 04:32 PM

If I'm not mistaken, the brake booster has an internal check valve, so you do not NEED to put another one inline.

Am I correct Oldguy?

**[email protected]** · 08-23-2009 09:22 AM

^^ Can anyone confirm this?

**jpulll** · 03-07-2015 09:38 PM

Originally Posted by [email protected]

^^ Can anyone confirm this?

I wish someone confirmed this lol

**diagnosticator** · 03-08-2015 12:18 AM

Originally Posted by jpulll

I wish someone confirmed this lol

It is not clear what you want clarification for.

**Let it snow** · 03-08-2015 04:31 AM

The brake booster does not have an internal check valve. The factory hose going to the brake booster is where the check valve is located.

**old guy** · 03-08-2015 06:31 AM

Originally Posted by [email protected]

If I'm not mistaken, the brake booster has an internal check valve, so you do not NEED to put another one inline.

Am I correct Oldguy?

The brake booster does not have an internal check valve. It has a vacuum passage that connects either side of the diaphragm and an atmospheric vent. When you press the brake pedal the vacuum passage closes and the vent to atmosphere opens. This puts all the vacuum on one side of the diaphragm and assists the pedal pressure to help stop the vehicle.

If you remove the SJP you should most certainly add a check valve. Otherwise you can apply a boost signal to the diaphragm instead of a vacuum signal if you press the brake pedal any at all while the manifold is under boost. I doubt that is very healthy for the brake vacuum booster.

And yes I am aware that the question was asked 6 years ago. Sometimes I am a little slow.....

**walky_talky20** · 03-08-2015 03:59 PM

On my B5, there exists a check valve in the OEM hard line that goes in between the brake booster and the false firewall. I'm not sure if that is true for every configuration, but in my case, the check valve function of the SJP was redundant. Upon deleting it, I did not replace it with another.

Redundancy would not be a bad idea though. These are your brakes, after all! If I had to choose a valve to install, I'd probably favor a booster check valve of full metal construction from an older Toyota (like an 85-95 Toyota Hilux).