PISTON RINGS/MISFIRES/FOULED SPARK PLUGS - The VCM mega thread - what is VCM, does my vehicle have it, what's so bad about it, and more

This thread explains all the key details regarding VCM. Rather than re-explaining everything about VCM to every new forum member, they can simply be directed here. Self-service FTW!

While there will be plenty of discussion in this thread, this first post contains the key information, so reading the rest of the thread (many pages) is not necessary. However, feel free to contribute to the discussion if you choose.

Although this is posted in the 2005-10 Odyssey forum, the information here will apply to all Odysseys 2005 and newer.

There are similar threads on both Piloteers and DriveAccord that you can check out if you own one of those vehicles. Coming from another forum? This one right here is the original!

What is VCM?
VCM stands for Variable Cylinder Management. It is a technology introduced in 2005 that is present in many Honda V6 engines. It shuts off some cylinders in the V6 in situations where the full power of all cylinders is not needed in order to save fuel. This is accomplished by using a solenoid controlled by oil pressure to unlock the cam followers from the rocker arms, which closes the valves and prevents them from opening throughout the piston stroke, stopping the combustion cycle in those cylinders. Fuel injection is also disabled in the disabled cylinders.

Besides the mechanical components in the engine to allow VCM operation, there are other components in the system. The most important component to know about is the active control engine mounts. When cylinders are disabled, it creates vibration from the motor, which the active mounts are designed to dampen so that you can't feel it in the cabin. Another part of the system is Active Noise Cancellation (ANC), which cancels noise from VCM by playing white noise through the vehicle's speakers.

Does my Odyssey have VCM?
Honda introduced VCM in the 2005 model year beginning with the 2005 Odyssey, and it has been used in Odysseys and several other V6 Hondas ever since. However, there are some Odysseys that don't have VCM in the 3rd generation (2005-10). Here is a list of Odysseys that are equipped with VCM:

2005-2010 - EX-L and Touring models only (unless the seats have been swapped, leather seats = VCM-equipped while cloth seats = no VCM)
- An easy way to identify if your 2005-10 Odyssey has VCM besides the seat material is the sticker on the plastic engine cover.

If you have a standard engine without VCM, your engine cover will look like this:



2005-2007 Odysseys with VCM will have an engine cover that looks like this (notice the i-VTEC instead of VTEC and the VCM font below that):



2008-2010 Odysseys with VCM will have an engine cover that looks like this (same as the last one except the VCM font is more prominent):

2011 and up - VCM is present on all trim levels

Are there different versions of VCM?
Yes. There are currently 4 different revisions of VCM:

VCM-1: The initial revision of VCM. It is capable of shutting off the rear bank of cylinders (cylinders 1-3).

VCM-2: The second and most problematic revision of VCM. It is capable of shutting off the rear bank of cylinders (cylinders 1-3) just like VCM-1, and it is also capable of shutting off one cylinder (cylinder 3) in the rear bank and one cylinder in the front bank (cylinder 4) at the same time, which means that VCM-2 affects an extra cylinder compared to VCM-1 and puts even more stress on cylinder 3.

VCM-3: The third revision. It is similar to VCM-1 in that it is only capable of shutting off cylinders 1-3.

VCM-4: The fourth and newest revision. Not much is known about this revision, but like VCM-3, it only shuts off cylinders 1-3. One key difference is unlike its predecessors that used varied camshaft profiles controlled by a solenoid, VCM-4 depressurizes hydraulic valve tappets to reach the same result of keeping the valves closed.

Different model year Odysseys are equipped with different VCM revisions:

2005-2007 Odysseys that are VCM-equipped (see the last section) have VCM-1:


2008-2010 Odysseys that are VCM-equipped (see the last section) have VCM-2:


All 2011-2017 Odysseys have VCM-2:


All 2018+ Odysseys have VCM-3:


No Odysseys are currently equipped with VCM-4.

How can I tell when VCM is active?
You may be interested in figuring out when VCM is active. On 2005-17 Odysseys, you may be able to feel/hear it as there may be vibrations. You will also see the green ECO light illuminate on the dashboard. However, while it is not common, it is possible for this light to be on even when VCM is not active. On 2018+ Odysseys, it's a little trickier, as there is no ECO light like the older models. You'll just have to listen carefully and feel for it.

On 2005-2010 Odysseys, the ECO light will be located as circled in the picture below:


On 2011-2017 Odysseys, the ECO light will be located as circled in the picture below:



Note that the ECO light will not come on and VCM will be disabled when a Check Engine Light is on for any reason.

A common misconception is the ECON mode button and the corresponding dash light on 2018+ Odysseys controlling VCM. The ECON mode has nothing to do with VCM. It affects things like shift points and throttle response to increase fuel economy.

What's so bad about VCM?
While VCM is a great idea in theory, in practice it has major issues.

During VCM operation, the valves on the disabled cylinders are closed off while the piston continues to move up and down. This creates a vacuum effect in the cylinder, allowing some oil to get sucked past the piston rings into the combustion chamber. This oil continues to collect in the combustion chamber until VCM disengages, at which point the cylinder must burn off the oil before resuming normal operation. This is one way that VCM can cause burning oil.

When VCM is used repeatedly for long periods of time, it can also cause the piston rings to get gummed up with buildup, preventing a good seal and allowing oil to get past the rings into the combustion chamber even when VCM is not operating. This is another way that VCM can cause burning oil.

Oil burning can cause oil fouling of the spark plugs, leading to misfires. The oil burning combined with the misfires will destroy your catalytic converters (not cheap to replace!) over time.

Besides these internal engine problems, VCM operation also puts stress on the active control engine mounts, causing them to wear out fast. These engine mounts are not cheap. One single mount can cost several hundred dollars in parts alone.

Simply put, VCM is gambling on your engine for a gain of 1-2 MPG at best. Gas is cheaper than an engine, especially given the very slight MPG difference.

It's worth mentioning that the general belief is that VCM-3 is more refined and tweaked compared to its predecessors and is therefore less problematic. VCM-3 has not been used in Odysseys for too long. So it's your call on whether you want to leave it alone or not. It will still eat up motor mounts faster at the very least, and like what was mentioned above, the MPG gains are minimal enough to where there's not much to lose, so there's not much reason at all to not disable it anyway.

This great video by speedkar99 shows a VCM engine taken apart so you can see how the parts of the system work together and how they cause problems. If you're interested, take a look:

I've owned several VCM vehicles and never had any issues. What's going on here?
These VCM problems are not consistent. Many factors play in to what (if any) problems you may see and at what severity. People who drove their vehicles hard when they were new have typically had fewer issues later on. People with VCM-1, VCM-3, and VCM-4 may experience fewer problems simply because there are fewer situations where VCM can engage and it will stay engaged for less time. But as mentioned in the previous section, the MPG gained is minimal at best, so what's the point in risking it?

If VCM is so bad, why does Honda still use it? Will Honda help me with my VCM related problems?
Honda would not spend the time and money to develop VCM unnecessarily. They're using VCM because it gets them CAFE credits from the EPA if they can maximize MPG on their vehicles. Without it, they'd be hit by penalties that would add up quickly given the large amount of vehicles that they sell.

Honda still refuses to acknowledge any problems with the VCM system as doing so would defeat the purpose as they would get in further trouble with the EPA. While there was a class action lawsuit against them regarding VCM, they settled it by offering an extended warranty on the piston rings (which they claimed were the actual cause of the problem) for 2008-2013 vehicles equipped with VCM. This warranty is now well past the expiration if you were lucky enough to be covered by it, and 2008-2013 doesn't cover a large chunk of VCM vehicles that are still affected, especially 2014-2017 Odysseys. While Honda dealerships will sometimes offer goodwill consideration for a piston ring replacement job on these vehicles, the cost can still be somewhat high, and because it's such a big, complex job, there's a good chance that more problems may be caused by technicians tearing apart the engine and putting it back together incorrectly. OdyClub members have experienced this in the past.

And for what it's worth, Honda has been phasing out VCM by simply phasing out the J-series V6 altogether. They're moving more towards the turbocharged 2.0L engine as seen in the 10th generation Accord. No more V6 = no more VCM. But then you get all the fun associated with a turbocharged engine. You win some, you lose some.

Honda has a new DOHC V6 design that debuted in the 2021 Acura TLX Type-S. Despite being a fairly significant redesign, VCM is equipped on this engine as well.

Okay. After reading this, I don't want VCM enabled on my vehicle. How do I disable it?
Good choice. Unfortunately, with the exception of VCM being inactive whenever a check engine light is on, Honda cannot include any built in disable switch for VCM because they wouldn't get the CAFE credits if they did. This means you must install an aftermarket device (also known as a VCM "muzzler"). However, do not worry. Installation is quite simple and an inexperienced user could likely install one in 15 minutes or less. All the devices come with good instructions for installation and don't require much in terms of tools (depending on which type you choose, you might not need any tools at all).

How do these disable devices work?
All these VCM disable devices work on the same concept: altering the coolant temperature reading sent to the computer to ensure that the reading never gets to 167 degrees Fahrenheit or higher.

By doing this, the computer thinks the engine is not fully warmed up yet, and it is programmed to not engage VCM until the engine has warmed up in order to ensure that excess wear is not caused by disabling cylinders on a cold engine, so it does not engage VCM. However, this does not affect the actual operating temperature of your engine, only the temperature reading the computer sees. And it is not a very significant change either.

Also, only the reading for one of the temperature sensors (known as ECT1, short for Engine Coolant Temperature Sensor 1) is altered. The other (ECT2) is left intact, so cooling fans will still operate normally, because cooling fans are controlled by ECT2 and are not at all affected by the ECT1 reading. Air/fuel ratio has also been found to be unaffected by using a VCM disable device. In fact, the only difference you'll notice is that your coolant temperature gauge may sit slightly lower than before when fully warmed up. However, there is no need to worry, as you will still be able to tell if your engine is overheating, as the gauge will still rise to hot like it would before.

There are absolutely no long-term risks of using a VCM disable device. In fact, there are more long-term risks if you don't use one.

Are there differences between the disable devices?
Yes. There are differences in features and compatibility.

The most important difference is that each disable device has a 2005-2006 version and a 2007+ version. These are not interchangeable, so if you have a 2005-2006 Odyssey, you will need the 2005-2006 version, and if you have a 2007+ Odyssey, you will need the 2007+ version. However, the particular VCM version your vehicle has does not affect this. A 2007 Odyssey would use the same muzzler as a 2008 Odyssey despite the latter having VCM-2 and the former having VCM-1.

Also, while all the disable devices work on the same concept, they accomplish it in different ways.

There are two categories for muzzlers: passive and active.

Passive muzzlers are good because they're cheaper, but they also require manual adjustment as the climate changes and are more like VCM suppressors rather than true VCM disablers, as they only disable VCM 90-95% of the time. VCM may come on briefly if you are in stop and go traffic.

Active muzzlers are more expensive than passive muzzlers but they are completely automatic. After installation (which is slightly more difficult as you must run a wire to the battery), adjustment is completely automatic using a microcontroller with no user input required, and VCM is disabled 100% of the time. Active muzzlers also usually are capable of turning themselves off in a real overheating situation so that you will be able to see the car overheating on the temperature gauge even faster than with a passive muzzler. The VCMTuner II also supports turning itself off if the car is detected to be idling. This is useful for some service procedures such as idle relearns where the computer needs an accurate temperature reading.

Generally active muzzlers are recommended over the passive variant, but if you cannot purchase an active muzzler for whatever reason, the passive muzzlers are still better than nothing if you can live with adjusting it every now and then and VCM coming on occasionally.

If you have a 2005-2010 Odyssey and choose to convert from the expensive active control engine mounts to the standard passive engine mounts, an active muzzler is required, as the passive mounts will be destroyed when VCM occasionally activates with a passive muzzler.

Which VCM disable device should I purchase?
There are 5 different recommended disable devices. They are recommended because they are made by trusted, well-known individuals and they have excellent customer service should you encounter a problem with them. Here they are, arranged from least expensive to most expensive along with where you can get them or view the exact price:
MaxMuzzler - Send a private message to @maxud or mention him in a reply to this thread and he will get back to you as soon as he can

VCMuzzler II - Send a private message to @verbatim, or if you can't, reply to this thread and verbatim will get back to you as soon as he can

VCMTuner - vcmtuner.com

S-VCM - svcmcontroller.com

VCMTuner II - vcmtuner.com

The following muzzlers are passive muzzlers:
MaxMuzzler (adjustable through resistance dial)
VCMuzzler II (adjustable through included swappable resistors)
VCMTuner (adjustable through resistance dial)

The following muzzlers are active muzzlers:
S-VCM
VCMTuner II

The VCMTuner and VCMTuner II are both CARB compliant, meaning that if you live in a CARB emissions state such as California or Washington, you should have no issues buying one and keeping it on for inspections and other work, and if anyone gives you a hard time about it, they come with a sticker showing the CARB compliance.

The choice of which type of muzzler and which specific muzzler you get for your vehicle is up to you. Consider the various factors as well as your specific situation to make your decision.

Will installing a VCM disable device void my warranty?
Installing a VCM disable device should not void your warranty. Many members have left their disable devices on when taking their vehicles to the dealership for service, and it has either gone unnoticed or noticed and ignored. As a matter of fact, in some cases the dealerships have even endorsed the device. However, if you are concerned about it, you can easily remove the disable device before you take it in for service and reinstall it afterwards with no harm done.

My car already has damaged piston rings, fouled spark plugs, and/or misfires. The dealer is quoting me an expensive piston ring replacement job. What can I do from here?
Even if your car already has one or more of those issues, it's NEVER too late for this.

Installing a VCM disable device and replacing all of the spark plugs should allow the piston rings to free up over time, and your engine should return to normal operation with VCM no longer engaging.

In very extreme cases, it is often suggested to add some Chevron Techron or equivalent to your gas tank and drive the car aggressively (hard acceleration is good, though wait until the engine warms up to do this) for a while to help free up the piston rings.

The bottom line is that you do not need to pay for an expensive piston ring replacement job and there's not much VCM damage that can't be undone. It is actually recommended to avoid the piston ring replacement job as not only is it expensive, but dealership technicians are known to frequently cause further issues when completely tearing down the engine for the job and putting it back together, leaving your engine in even worse shape than it already is. There are members of this forum who can attest to this.

What are some other common issues to watch out for that can be caused by the effects of VCM?
There are some other issues that can come up that are seemingly unrelated to VCM, but they are indeed caused by VCM. It's important to disable VCM before fixing these things as otherwise the problem may return. Here are some of these problems:

Torn Intake Hose:
It is common (especially on VCM-2 equipped vehicles) for the main intake hose to tear, causing issues with rough idle and stalling, especially when shifting into different gears. The cause of this issue is VCM wearing out the motor mounts. Once the motor mounts fail, there is excessive engine movement, which tears the intake hose. The complete fix to this is to replace the intake hose and inspect the motor mounts (replacing if needed) after disabling VCM.

Worn/Pitted Camshafts:
VCM-2 engines are known to have issues with the camshaft (typically the front bank camshaft) wearing out prematurely causing a ticking sound. Disabling VCM early can help prevent this, but it's still possible that it could happen later on, especially if VCM was active for a large number of miles.

Spool Valve Oil Leak/Fried Alternator:
VCM-2 engines are also equipped with a spool valve in the front cylinder head to enable disabling cylinder 4. This spool valve is positioned in a spot that causes oil leakage from it to go straight into the alternator that is positioned directly below it. Unfortunately, disabling VCM does not mean this spool valve will not eventually leak down the road as it will still be holding back oil pressure.

It is highly recommended that you occasionally monitor this area and get it fixed as soon as possible once you notice even a small leak from it to avoid damage to your alternator.

Lack of low end power:
If you drive a non-VCM engine and a VCM engine, you may notice that the non-VCM engine feels like it has more power, especially at lower RPMs. This is not really an issue as much as a consequence of the design of VCM.

Due to the way VCM works (it effectively does the opposite of what VTEC does), engines equipped with VCM-1 and VCM-2 are not equipped with Honda's classic VTEC. This can manifest itself as a lack of low end power. VCM-3 engines are equipped with VTEC on the front bank of cylinders.

Can I trust my engine to be reliable after disabling VCM?
Yes. As long as you do regular maintenance like you would with any other car, once you disable VCM, your engine will be just as reliable as a Honda engine that doesn't have VCM. Enjoy the ride with all 6 cylinders working all the time!

Note: if given advice regarding VCM from users named '191145' or 'tdelco', we would strongly encourage you to ignore the advice from these known trolls.