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Discussion Starter · #1 · (Edited)
I know there's plenty of information out there already about VCM, but it's all quite dispersed and it hasn't really been put together until now.

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 2008-12 Accord forum, the information here can be applied to Accords across multiple generations.

There are similar threads on both OdyClub and Piloteers that you can check out if you own one of those vehicles.

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 Accord have VCM?
Honda introduced VCM to the V6 Accord in the 2005 model year for the hybrid version only, and it has been used in other V6 Accords in the 8th generation (2008-12) and 9th generation (2013-17). However, there are some V6 Accords that don't have VCM, so to help you figure out what you have, here is a list of Accords that are equipped with VCM:
  • 2005-2007 Accord Hybrid
  • 2008-2012 Accord V6 Sedan
  • 2008-2012 Accord V6 Coupe w/ 5 speed automatic transmission (V6 coupes with a manual transmission do not have VCM)
  • 2013-2017 Accord V6 Sedan
  • 2013-2017 Accord V6 Coupe w/ 6 speed automatic transmission (once again, V6 coupes with manual transmissions do not have VCM)

As the Accord V6 was discontinued beginning with the 10th generation in 2018, VCM is not present in the 10th generation Accord and newer models.

Are there differences in the VCM systems?
Yes. There are currently 3 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 and newest revision. It is similar to VCM-1 in that it is only capable of shutting off cylinders 1-3.

Different model year Accords are equipped with different VCM revisions:


2005-2007 Accord Hybrids are equipped with VCM-1.

2008-2012 Accords that are VCM-equipped have VCM-2.

2013-2017 Accords that are VCM-equipped have VCM-3.

How can I tell when VCM is active?
You may be interested in figuring out when VCM is active. On 2005-2012 Accords, when VCM is operating, you may be able to feel it kick in and you will 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 2013-2017 Accords, 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. Even then, it may be difficult.

Note that the ECO light (if equipped) 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 2013-17 Accords 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 good in theory, in practice it has some 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 been used in Accords since 2013 and seems to be a little less problematic, although the overall concept is still flawed. So it's your call on whether you want to leave it alone or not. It will still stress the motor mounts 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 to not disable it anyway.

This 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 and VCM-3 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. 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. Some owners 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. What can I do?
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. If you have a 2005-2006 Accord, you will need the 2005-2006 version, and if you have a 2007+ Accord, you will need the 2007+ version. However, the particular VCM version your vehicle has does not affect this. A 2009 Accord would use the same muzzler as a 2016 Accord despite the latter having VCM-3 and the former having VCM-2.

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.

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 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.

If you have a 2013-2017 Accord and a KTuner, there is an option in KTuner to disable VCM as well. While I would not purchase a KTuner just for this, if you already have a KTuner or plan on getting one for other reasons and have a 2013-17 Accord, I would recommend disabling it using KTuner.

Will installing a VCM disable device void my warranty?
Installing a VCM disable device should not void your warranty. Many owners 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 owners 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, but this can be an issue on most J series engines) 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 worn motor mounts from VCM operation. Once the motor mounts fail, there is excessive engine movement, which easily 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:
Many 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, engines equipped with VCM are not equipped with Honda's classic VTEC. This can manifest itself as a lack of low end power.


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!
 

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Excellent! Thanks for posting WiiMaster! I've asked the question "how does VCM cause oil burn" on the forum and no one answered. I finally understand. I knew there had to be more down-the-line issues to shutting off these cylinders. I installed S-VCM (10 minutes). I only have about 2k miles on it in 90-100 degree weather and it's fine. 2MPG average drop in 100% city driving but as said, it's way cheaper than an engine overhaul.
 
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Discussion Starter · #3 ·
It's not just Honda either. Others, like GM, have tried and failed as well.

Honda's new DOHC V6 (which still seems to be considered part of the J series family interestingly enough) that they're introducing in the Acura lineup doesn't have VCM. Makes me wonder what the future is for VCM.
 
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Discussion Starter · #5 ·

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@WiiMaster , this is a really good write-up. Thanks for doing it.

When the extended warranty for VCM expired on my Accord, I decided to turn it into a rolling VCM test bed - it's unmuzzled at 9 years/179,000 miles, and to date, no issues with oil consumption, fouled plugs, or creaky motor mounts. That said, I don't recommend what I'm doing for anyone else. If you've got an 8th gen V6, then I'd suggest following Commander Data's advice.

And @TheBusch , the J-series isn't going anywhere, at least not for Honda's largest vehicles. Given that the 4th gen MDX uses a J-series and not a turbo four, I think there is a good chance that the Pilot, Ridgeline, and Odyssey will continue to use that engine.
 

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Discussion Starter · #8 ·
And @TheBusch , the J-series isn't going anywhere, at least not for Honda's largest vehicles. Given that the 4th gen MDX uses a J-series and not a turbo four, I think there is a good chance that the Pilot, Ridgeline, and Odyssey will continue to use that engine.
You're not wrong. The J series is here to stay. But as I outlined earlier, they've already dropped VCM in their new DOHC J30. And they're using that in the MDX Type-S and TLX Type-S, cars that have typically had VCM.

This signals to me that the J35's (which is the only displacement to have VCM with the exception of the 3.0L in the early Accord Hybrids) days are numbered. I think they're going to move to turbocharged J30s in their larger vehicle lineup at some point in the future, similar to how they replaced the Accord J35 with the turbocharged K20.

Won't this die off as Honda stops using the NA V6 anyways?
Probably. But it's still likely to stick around for another 5 years at least.
 
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Discussion Starter · #10 ·
VCMTuner II is now CARB compliant as per the VCMTuner site, giving it another advantage over the S-VCM.
 
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Discussion Starter · #12 ·
2012 accord v6 need to disable vcm?
Need is a strong word. What I can tell you is you do have VCM, and if I owned that car, I would disable it.
 

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Great write up WiiMaster. I added an S-VCM to my car some time ago and it has worked flawlessly since. I don't drive enough any more to notice the slight drop in mileage. The fun factor of having the V-6 under foot all the time has been gratifying too.
John WL - get a VCM tuner. I can vouch for the S-VCM.
 

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since i installed my vcm tuner 2 my car runs smoother, no vibration as before when it went into eco mode. it always felt like the trans was trying to find the rite gear
 

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since i installed my vcm tuner 2 my car runs smoother, no vibration as before when it went into eco mode. it always felt like the trans was trying to find the rite gear
Interestingly my car never had any of the 'symptoms' associated with a problem with ECO mode.
My car did have a barely audible 'miss' when listening at idle to the exhaust pipes.
Investigation found a badly fouled plug which also had a cracked insulator on the center electrode.
It never ran 'rough' like I would have expected it to if that plug weren't working at least part of the time.
Car is smooth as silk now with lots of power. It has never used oil either.
 

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Discussion Starter · #17 ·
How can I do? go to dealer and upgrade the pcm software or get a vcm tuner?
Honda isn't going to help you disable VCM.
 

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Just to keep things all in one thread, here's a picture of my fouled plug after I had wire brushed it for the photo. The gap was almost completely closed up with carbon deposits. The car drove perfectly fine though, no noticeable miss. You could hear a slight 'pop' at the exhaust pipe at idle indicating a miss but it was barely audible unless you got right down next to the tail pipe and listened closely. Car never used oil either so I count myself lucky in that regard.
Household hardware Audio equipment Engineering Automotive ignition part Cylinder

This happened at @49k miles too. Only came to my attention when I got a CEL on startup when on a trip to my brother's place.
 

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was this plug from the rear?these are from mine,127,000 miles i think they are the stock plugs.back 3 are from the rear
Light Wood Finger Audio equipment Cable


I've
never seen the porcelain crack like that.
 
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