2011-2016 Cruze 1.4L PCV System Explained
I made a video to help better explain how this whole PCV system works to supplement this article.
The purpose of this post is to explain the function of the PCV system in the 1.4L Turbo engine so those of you who are having issues or trying to help people have some idea of what is going on and where to look for potential trouble spots. We will start by assuming you know what a PCV system is designed to do. If not, stop here and go to google. Return when you understand the basics of what A PCV system does. Basic mechanical knowledge is required. I will attempt to explain this by walking you through the path of the PCV system. Below is an outline of the whole system and the direction the PCV gas flows, and each step will include any pictures I could find that show the actual component described. The terms "non-return valve" and "check valve" are used interchangeably. A check valve allows a gas or liquid to move in one direction but not another.
1 We start with the crankcase that has built up pressure, under a normal operating vehicle. We exit the crank case through the cylinder head at the two long ports at the bottom of the following image.
2. Those two ports feed into the valve cover, at the two long ports on the right side of the image below.
3. From there, we travel through a baffled oil separator system. THIS IS WHY WE DO NOT NEED A CATCH CAN. This pathway inside the valve cover is tasked with separating oil vapor from the PCV gas traveling through it. From there, we exit into the small port on the left (refer to arrow at the left of image above), to go back into the cylinder head. Notice the corresponding port on the cylinder head (arrow at the top of the image)?
4. Next, we find ourselves in the intake manifold, which is pictured below. Inside this port, there is a check valve (which GM refers to as a non-return valve), pictured in the next two images. Note, this is not a ball (as it has been previously referred to). It is a non-return/ check valve, that more closely resembles a specifically shaped nipple.
5. A corrugated hose comes out of the intake manifold, which has an open path from the PCV system and does not have to go through the non-return valve.
6. We arrive at the top of the below image, where there is ANOTHER CHECK VALVE.
7. Lastly, we exit to the turbo housing at the turbo's inlet (see oil streak above).
In case you missed it:
The crankcase is under vacuum whenever the engine intake is under vacuum; the check valve valve in the intake manifold opens and pulls all crankcase gases while keeping the check valve at the turbo inlet closed. When the engine produces boost in the intake (during acceleration or uphill driving), that check valve closes due to the air pressure inside the intake manifold, because we don't want to pressurize the PCV system. When this happens, the extra crankcase pressure is relieved through the check valve at the turbo inlet. PCV gas at the intake manifold check valve flows into the intake manifold but not back into the PCV system, and air at the turbo inlet housing flows into the turbo inlet, but not back into the PCV system. Both check valves allow PCV gas back into the intake; one before the turbo and one after the turbo. I want to make sure this is clear.When things go wrong:What happens if the check valve in the intake manifold fails (Step 4)?
- Excess vacuum is produced on the PCV system internals when intake is under vacuum, which may pull more PCV gas than the oil separator is capable of filtering. Excessive intake vacuum may be applied on the crank case, which may also cause premature failure of the regulator diaphragm.
- Boost is leaked from the intake manifold into the PCV system. You may not notice this happening until more symptoms show up. The boost leak seems to overwhelm the flow capacity of the check valve at the turbo inlet, and causes positive crankcase pressure. This positive crankcase pressure then causes the turbo to leak oil internally, the CPASV seals to leak, the oil pan gasket to leak, and oil to trip from the throttle body at the connection to the intake tube.
- Excess positive crankcase pressure caused by the boost leak will cause the burst disk in the valve cover to rupture. Since the check valve itself may not show any other symptoms of failure, you may find yourself constantly replacing intake manifolds until you address the root cause.
- In the event that the turbo inlet check valve is stuck in addition to the intake manifold check valve disappearing, oil consumption will increase. See below under "if you are burning oil."
Notes: The intake manifold check valve can either disappear completely due to fatigue (it's rubber after all) and be ingested by the engine through the intake, or it can be stuck open. To inspect this check valve, pull the corrugated hose off of the intake manifold, and shine a light in there. If you see nothing, dip a cotton swab in rubbing alcohol and clean the side facing the vehicle's firewall as far down as you can since it may just be dirty. If there is still nothing there, your check valve is gone. IMPORTANT: failure of the check valve does not automatically result in elevated oil consumption.
What happens when the check valve at the turbo inlet fails (Step 6)?
- In the event that the check valve at the turbo inlet is stuck closed, the burst disk can fail.
- Excess pressure will build in the crank case, which will prevent the turbo bearing housing from draining oil, and will seep oil past the turbo seals to be burned in the exhaust or through the intake. (Walker Morgan noted this one). In the event that this occurs, oil consumption will increase.
Notes: If you are burning oil, remove the corrugated line and blow into it. If it does not blow freely, your check valve is stuck closed. Wipe the oil from your mouth, and replace it. A second possibility is an intake manifold gasket failure around the PCV ports in the first picture above.
What happens when the PCV regulator diaphragm (Step 8) fails?
- Excess vacuum or boost produced on the PCV system by the intake manifold check valve (whether or not it is good) being open will cause unmetered air to flow through the vent on the cap and may trigger a check engine light. Refer to "related service codes" at the end of this article. You will hear a hissing sound in the engine bay.
- If the either of the above check valves have failed, you may find oil vapor sprayed in the proximity of the cap vent.
Notes: The PCV regulator diaphragm may fail from fatigue, or it may fail in the event that either of the PCV check valves fail and cause excess vacuum or excess PCV pressure. A failed PCV regulator diaphragm may or may not be a symptom of another root cause.
What happens when the corrugated hose fails?
- The corrugated hose may crack and develop a vacuum leak. If this happens, unmetered air will enter the the intake under vacuum when the intake manifold check valve is open. If severe, this may trigger a check engine light. Refer to "related service codes" at the end of this article.
What to do if these components have failed:
- Refer to GM Bulletin PIP5198C. Link good as of 8/28/17: https://gm.oemdtc.com/2398/pip5197c-...olet/2?fref=gc
- Replace the defective components
No tutorial currently exists for replacement of the intake manifold, the corrugated hose, or the turbo inlet check valve. Any volunteers?
- I've presented a retrofit solution for the intake manifold check valve failure in the following thread that will cost 1/2 to 1/3 that of a new intake manifold while lasting much longer:
Related Service Codes:
P0106 P0171 P0299 P0507 P1101 P2096