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[Moderator note: this FAQ is posted for information only and is neither a promotion nor an endorsement of the Muzzler. Do your own due diligence for any aftermarket product you install on your vehicle.

For any comments or discussion, please start a new thread. This thread is closed.

Note: this FAQ is authored by verbatim, the provider of the Muzzler.

I am starting this post to help summarize with a FAQ, what’s been discussed in various threads regarding VCM in the 2017 models and the VCMuzzler II. There are many threads already and it's hard for newcomers to weed through the information and sometimes misinformation posted in them.

Q. What is the VCMuzzler II and what does it do?
A. It is a device that plugs in line with your Engine Coolant Temperature sensor (ECT1) to effectively lower the perceived temperature reported to the ECU. The goal is to lower the temperature just slightly so that the ECU thinks the temperature of the engine is just below full operating temperature, hence disabling VCM from engaging.

Q. What is the difference between the VCMuzzler and the VCMuzzler II?
A. The original version had one hardwired resistor. It became apparent early on that due to the variability between vehicle cooling system components, one resistor fits all was not sufficient. The VCMuzzler II comes with the ability to switch resistors easily. The original version is discontinued.

Q. Why would I want to disable VCM?
A. There are many discussions on this on many forums. VCM (Variable Cylinder Management) is a feature on Honda and Acura vehicles whereby cylinders are deactivated during light load cruising conditions in order to increase fuel economy numbers. However, it can lead to problems including but not limited to: excessive oil consumption; spark plug fouling; misfires and misfire codes; worn engine mounts; vibrations during VCM activation; hesitation when accelerating out of VCM mode; sense of a lack of power when cruising. Honda has admitted to some of these issues with the loss of their class action lawsuit, warranty extensions and TSB’s. GM has similar issues with their ACM technology.

Q. How hard is it to install?
A. Most people can install it in less than 5 minutes. It is plug and play.

Q. Does the VCMuzzler II come with instructions?
A. Yes, it comes with a 5 page color illustrated manual.

Q. If Honda is aware of the issues, why would they not discontinue it or offer an option to turn it off?
A. With VCM technology in its V6 vehicles, Honda benefits from an EPA / CAFÉ regulations rating. Should Honda remove it or offer the driver an option to disable it, they would lose this rating and be subject to penalties for not meeting the regulations.

Q. VCM has been out for a while now on Honda vehicles. Surely they've made improvements to it since the original problems, haven't they?
A. The technology has not improved much since they introduced it. While Honda claims they have improved the technology since the problems they experienced with the lawsuit, TSB's Warranty extensions etc, all they have really done is change the ECU programming to ensure VCM is not active for too long at any given stretch. The components are all the same. The reason for this is that when cylinders deactivate, the oil ring cannot keep oil out of the cylinders. This is why to this day, I'm hearing reports of new 2016 ody's, pilot and accords with high oil consumption, and I'm sure the reports on the 2017 ridgeline is not far behind. When reported to Honda, they say that up to 1 quart per 1000 miles is "normal". The problem with VCM allowing too much oil to bypass at one time is that when too much oil is present, you get detonation, which permanently deforms the oil rings. This causes even more oil bypassing, which leads to plug fouling and misfires. So by changing the ECU to fire all of the cylinders once in a while during extended cruising, they're burning off the excess oil by mixing it with fuel before it accumulates too much and causes detonation. Therefore, the technology has not vastly improved over time; they're just masking the problems a little better and trying to avoid the big ones.

Q. I have a newer Honda that has an "ECON" button on the dash and a light showing when ECON mode is on or off. Does this mean I can disable VCM with this?
A. No. VCM is always active, the ECON button does nothing to disable VCM. If it did disable VCM, Honda would lose it's rating with the EPA and would be subject to fines. The ECON button is all about acceleration, VCM is about cruising. When you put your vehicle in ECON mode with the button, the ECU tries to save you fuel by smoothing out the response to your accelerator inputs by giving the engine less gas, changing timing and gear selection etc., so that your jackrabbit attempts at accelerating from a stop are tamed down to a little more turtle-like acceleration. VCM is about dropping cylinders when you're cruising and there's no reason, in Honda's mind, to deactivate VCM while cruising because they feel that it is seamless to the driver, plus they don't want to have to pay penalties to the EPA. Your ECON button is doing nothing to deactivate VCM. The perception that it is, is coming from the fact that Honda has removed the "ECO" light from vehicles that have the ECON button and light to remove confusion to the driver. The ECO light used to be the signal that VCM was active.

Q. Which vehicles does the VCMuzzler II work on?
A. The following vehicles that are equipped with VCM.
Accord & Accord Hybrid 2005+
Crosstour 2010+
Pilot 2006+
Odyssey 2005+
Ridgeline 2017+

RDX 2013+
RDL 2013+
MDX 2014+
TLX 2015+

Q. Does the VCMuzzler II change the operating temperature of my vehicle?
A. No, your vehicle’s cooling system is unaffected. The fans operate as usual as they are turned on by ECT2. The actual operating temperature of your vehicle is unchanged.

Q. What can I expect to happen after installing the VCMuzzler II?
A. Your temperature gauge at full operating temperature will read just slightly lower. Your ECO light on your dash board (if equipped) should not come on during normal driving and VCM will not engage. In extended idling conditions i.e. traffic jams, the engine temperature may creep up to slightly above the VCM threshold, resulting in seeing the ECO light for about 30 seconds when resuming driving. After this, the ECO light will go out and VCM will be deactivated again.

Q. Will I notice any difference when driving after the VCMuzzler II is installed?
A. Just about everyone reports an improvement in the drive-ability of the vehicle. It's not something you notice until VCM is deactivated, then you realize that having full power all the time while cruising is better. You don't notice the very slight transitions between VCM mode and non-VCM mode until they're gone.

Q. Will I still be able to know if my engine overheats?
A. Yes. Your temperature gauge reads only slightly lower. Monitor your engine temperature (as you always should) and if you see an abnormal rise well above this new lower reading, then your engine may be overheating. You will still get an overheat warning on your dash if your engine overheats.

Q. Are there other systems that will be affected by using the VCMuzzler II?
A. There have been no reported detriments to using the VCMuzzler II. The idle speed, Air/fuel ratios, timing, shift points etc. are all unaffected. This is due to the fact that the perceived engine temperature is only slightly decreased and the engine is well out of cold startup mode. The engine and transmission operate as if the vehicle was at full operating temperature. Because VCM involves the deactivation of cylinders, the ECU ensures the engine is COMPLETELY hot before deactivating cylinders to ensure the oil is up to temperature and the cylinders are being lubricated properly. Deactivating a cold cylinder would mean excessive engine wear and uneven temperatures across the engine, resulting in improper piston clearances / ovality etc. This is why VCM can be deactivated with this slight temperature drop without affecting other systems.

Q. I’m experiencing vibrations while driving. Will the VCMuzzler II eliminate them?
A. If the vibrations occur only when the ECO light is on during cruising conditions, then it’s very likely that the VCMuzzler II will eliminate them. Vibrations can occur for many other reasons, including wheel out of balance, wheel bearings, warped brake rotors, worn engine mounts etc. The VCMuzzler II will not eliminate vibrations from other sources.

Q. My vehicle has excessive oil consumption and / or misfires. Will the VCMuzzler II solve these issues?
A. It’s hard to say for sure. A great many people have reported either no more oil consumption or a reduction in the amount consumed. Some have reported no more misfires. There are some that report no change to either. It all depends how far gone your vehicle is with regards to these issues. Excessive oil consumption is a result of improper loading of the oil ring on your piston and eventually it will plug off and no longer work as it should to effectively wipe oil from your cylinder walls. If it isn’t in too bad of a condition, using the VCMuzzler II to fire the cylinder all of the time may reverse this and lead to a decrease or elimination of oil consumption. If the oil ring is too far gone, the damage can’t be reversed. The same is true for plug fouling / misfires. There’s no way to predict an improvement or not, but many have reported improvements or a complete absence of any further problems.

Q. Have there been any bad consequences reported from using the VCMuzzler II.
A. No, the response has been overwhelmingly positive with no detrimental effects reported. Just about every user reports an increase in driving enjoyment due to having 6 cylinder power all the time with reduced hesitations. Most, if not all of the reported issues revolve around the resistor selection, which are easily resolved.

Q. What will happen to my gas mileage?
A. Most have reported only a slight drop of 1 mpg. Some report either no change or an improvement. The improvement may be because of a change in driving habits as some, including myself, would tend to unconsciously accelerate more than necessary to kick out of ECO mode when approaching hills or other conditions where more power was needed during cruising conditions. At any rate, the slight drop of 1 mpg is acceptable to most. There have been no reports of more than this.


Premium Member
86 Posts
Discussion Starter #2 (Edited)
Q. Do I have to remove the VCMuzzler II before I take my vehicle in for service or an emissions inspection?
A. If the vehicle is under warranty, I would recommend removing it. There’s no practical reason why Honda would void your warranty for using the device, but any modification to the vehicle can be used as attempted grounds to void the warranty by some unscrupulous dealers. I have not heard of any cases of this to date. Everyone so far that has left it in for a service trip has reported either it was not even noticed (as it looks OEM) or in a few cases, the service people have actually recognized it for what it is (I guess word is getting around). In none of these cases have they said that it’s a bad thing and should be removed. In a couple cases, the service person endorsed it, saying it’s a good thing, others will not endorse it (presumably because it’s not OEM) but do not downplay it either. I have sold some to dealerships and repair shops.
For emissions inspections, again, some report leaving them on and passing with no problem. The self-diagnostics all pass with the VCMuzzler II installed. There have been no reports of failing an inspection because the VCMuzzler II is installed.

Q. Why are there 5 resistor connectors supplied with the VCMuzzler II?
A. The different resistors are to account for variances between vehicles cooling system components such as thermostats, sensors, cooling system fluid and condition and radiator condition as these variances can result in slightly different operating temperatures. Climate can play a role in selection as well. You really can't tell what you need until you try it. Note that earlier versions of the VCMuzzler II were only supplied with two resistors. In those cases, if you need a resistor other than the two supplied, an optional resistor pack is available.

Q. How do I decide which resistor to use?
A. Always start with the Blue 82 ohm resistor (installed on the harness when you receive it) and if necessary move up or down according to the troubleshooting chart in the instruction manual.

Q. My newer model Honda does not have an ECO light that comes on and goes off while driving. How do I know that the VCMuzzler II installed on my vehicle is actually disabling VCM?
A. Newer model Honda's do not have an ECO light, which is the indicator in the older models on whether VCM is activating or not. In the newer model Honda's the ECON button is independent of the VCM system, and VCM is active regardless mentioned above. There are a couple of ways to verify that the VCMuzzler is working on newer model Honda's.

The first is to purchase an inexpensive OBD II scan tool. These can be found at your local parts store or on ebay. There are models that have their own display, or you can get ones that plug in and transmit the data to an app that you install on your smartphone. Either one will have a mode for monitoring sensors. If you look at the ECT (engine coolant temperature) reading and it is staying below 167°F the majority of the time, then you are deactivating VCM during that time. Occasional creeping above 167°F after idling in heavy traffic is not a big concern because VCM will only engage for less than a minute after you get going again and the temp comes back down. 167°F is the VCM threshold for every 3.5L engine with VCM that Honda has produced since 2005. So that's a positive way to ensure VCM is deactivated on your newer model Honda.

If you don't want to buy the scan tool, the second way to ensure you are deactivating VCM is to use the highest resistor you can without getting a CEL (check engine light). This method is less accurate, but cheaper as you don't need to purchase anything. In this method, you would start with the red resistor. If you don't get a CEL, then VCM is most certainly being deactivated the vast majority of the time as the red resistor lowers the perceived temperature to the ecu below 167 degF for the majority of driving conditions on all Honda's. If, however, you get a CEL with the red, then you don't need that much resistance and the blue will do the job just fine. Getting CEL errors (usually showing on the display as "check emissions system") is not a troubling event, because you know it's related to the VCMuzzler causing the reported engine temp to be too low to the ECU. These CEL codes can be cleared either by switching to the blue resistor and driving it for a few days, which allows it to clear on its own, or disconnecting the battery for a few minutes, which will clear it immediately.

Q. How do I know if I’m using too high of a resistor?
A. If you get a Check Engine Light (CEL) warning on your dash that says “Check Emission System” and the code returned is “P0128 Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature)”. If you don’t have a code reader, you can go to your local parts store and they will read and tell you the code for free. If you see this CEL right after installing the VCMuzzler II or increasing the resistance, then this is almost certainly the error code you will get. This code is generated when the ECU perceives the engine temperature to be outside of the acceptable range of the thermostat (which is usually pretty generous).

Q. I got a CEL on my dash after installing the VCMuzzler II or switching resistors…What should I do?
A. First of all don’t panic. The CEL can be triggered for two reasons. Firstly, you may have installed it when the engine was not completely cold. It should always be installed or resistors should be changed first thing in the morning before the vehicle has been started. The second reason may be that the resistance is too high for your vehicle.
If the CEL was a result of it being installed while the engine was too warm, the CEL should clear on it’s own after a few drives or it may take a few days.
If the CEL was a result of too much resistance, it either will not clear on its own after a week, or it will clear and then return. In this case, the resistance will need to be decreased… see the above two FAQ’s.
If you wish to clear your CEL manually, disconnect the battery for a few minutes.

Q. I’ve been using the VCMuzzler II for a while now and all of a sudden I got a CEL. What happened?
A. It could be your cooling system has changed slightly and you have the P0128 error. It may also be that the ambient temperature has dropped due to the seasons and this has affected your operating temperature. However, it might be another error completely unrelated to the VCMuzzler II. You should read the code if you have a reader or get it read for you for free at an auto parts store. If it is the P0128 code, it may just have been an anomaly and it may clear again on its own after a while. If it doesn’t, you may have to change to a lower resistance. If it is a different code than P0128, then you’ll have to address whatever the code is telling you.

Q. What is the cost? Why is it so expensive? Why is it so inexpensive? How do I order?
A. The cost is based on many things, supplier costs, ebay and / or paypal fees increasing and on the time it takes to manufacture as I make each one by hand, not with high volume manufacturing equipment. I adjust the cost occasionally due to increasing costs. Some wonder why I don’t charge more. If you’re interested in purchasing and wish to know the cost, send me a PM. If you know you want to purchase, send me your name, shipping address, paypal email address and the year and model of your vehicle. I’ll send you a paypal invoice and once paid, it ships along with the instruction manual.

Q. How long does it take to ship? How long does it take to arrive?
A. I usually ship next business day, sometimes it can be up to two or three days at the most. Delivery time from ship date to the US is on average 2 weeks, but can take up to three or more occasionally. The main delay is always in US Customs as they are being shipped from Canada. US customs processing times are very erratic. Shipments within Canada take 3-4 business days.

Q. I have not received my VCMuzzler II yet and it’s been a long time. What can be done?
A. I can’t initiate a claim until 30 days past the ship date. Once 30 days has passed, I can initiate a claim and send out another. This has only been necessary in a few cases.

Q. A wire or resistor has pulled out of the connector terminal. What should I do?
A. You cannot repair it once this has happened. To prevent this, never pull on the wires or the resistors, only pull on the connectors themselves and take care not to put tension on other wires when doing so. If this does happen, PM or email me to arrange a repair.

Q. How long will the resistors last?
A. It will likely outlast you and your vehicle. The resistors are much higher rated than necessary and not taxed very hard at all.
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