Honda Odyssey Active Motor Mount (ACM) Vibration Failures: Cost of OEM Hydro Mount Replacement
You’re sitting at a stoplight, foot on the brake, and the steering wheel starts to vibrate. Then you accelerate and feel a thunk from under the hood, like something is shifting that shouldn’t be.
If you own a Honda Odyssey with the 3.5-liter V6, this is often the Active Control Motor Mount (ACM) system. These sophisticated mounts are prone to failure, often leaking a thick fluid. While the repair isn’t cheap, understanding the costs and causes can help you make the best decision for your van.
TL;DR
Honda Odyssey ACM failures cause cabin vibrations, clunks during gear shifts, and rough idling. These costly mounts are the front and rear active engine mounts—they can cost over $600 each for the part alone. A full professional replacement of multiple mounts costs around $2,500. While you can sometimes replace just one faulty mount, replacing all of them at once can save you money on labor in the long run. On some models, disabling VCM can extend the life of new mounts.
The ACM System: What It Is and Why It Fails
Honda’s ACM system was introduced to help reduce the engine vibrations inherent with the Variable Cylinder Management (VCM) system, which shuts down cylinders for fuel economy . These “active” engine mounts are computer-controlled and can change their stiffness to counteract vibration .
There are two main active mounts on the Odyssey: a front mount and a rear mount . They are filled with a fluid that helps them perform their damping function . When an ACM fails, it often leaks this fluid and can no longer effectively isolate engine vibrations .
Cost of OEM Active Motor Mount Replacement
The primary cost drivers are the parts, specifically the active mounts, and the significant labor involved.
Part Costs (OEM):
- Front/Active Engine Mount: Typically an assembly with an ACM control unit. For many models, this part can cost around $500 or more .
- Rear ACM Assembly: Another large and expensive component, often costing between $400 and $600 .
- ACM Control Unit: For newer models (2020+), the system’s control module itself can cost over $400 .
Total Replacement Cost: For a repair that replaces multiple broken mounts (which is common), the cost can be significant. One Car Talk reader was quoted about $2,500 for labor and materials to replace front, rear, and side engine mounts . Industry experts note that this estimate is “in the right ballpark” for a professional repair .
Symptoms of a Failing ACM
Recognizing these symptoms can help you catch a failure early:
- Vibration at Idle: You’ll often feel a shake in the steering wheel or cabin when stopped in Drive .
- Clunking or Thumping: You may hear or feel a loud thud when shifting from Park to Reverse or Drive, or when accelerating from a stop .
- Engine Movement: With the hood open and the vehicle in Drive with the brakes on, the engine may visibly shift more than an inch when revved .
- Fluid Leaks: A visible leak of thick, oily fluid (often black, brown, or blue) from the mount area is a clear sign of failure .
Frequently Asked Questions
What is the difference between an ACM and a standard motor mount?
An ACM is an active, computer-controlled mount that changes its stiffness to counter engine vibration. Standard mounts are passive, solid rubber components .
How do I test if my ACM has failed?
A common test is to have someone shift the vehicle between Drive and Reverse while you observe engine movement. You can also disconnect the vacuum to the control solenoid; if the idle quality doesn’t change, the system may have failed .
Why are ACM replacements so expensive?
The parts are costly (OEM active mounts can be over $500 each), and the labor is extensive. Replacing rear mounts often requires lowering the subframe, adding significantly to the time .
Can I just switch to cheaper standard mounts?
Some owners have successfully converted to standard mounts after disabling VCM, but opinions are mixed. It’s an option, but it may not provide the same level of cabin refinement .
Is it necessary to replace all the mounts at once?
No, but it’s often recommended. If one mount has failed, the extra strain can accelerate wear on the others. Replacing them all at once can save on future labor costs .
If you’re out of warranty and want to prolong the life of your new mounts, the owner community is strong—disabling the VCM system with a deactivator kit can help prevent the conditions that stress your new mounts. Investing in OEM or high-quality aftermarket parts and a professional installation is the best way to restore that silky-smooth Odyssey ride.
Have you had to replace active motor mounts in your Odyssey? Share your experience and cost in the comments below.
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