Recently I saw a bumper sticker that read, “Don’t believe everything you think.” It brought to mind another saying I once heard, “Someone’s perception is their reality.” Doesn’t necessarily mean it’s true, it’s just what they perceive to be true. Another quote that came to mind originated from the movie American Beauty, “Never underestimate the power of denial.” These quotes in some way relate to an old proverb that says “Every way of a man is right in his own eyes.” 

In diagnosing problems with vehicles, every now and again what one thinks they know blinds them from seeing what is really causing the problem. When this occurs, it typically takes place with a vehicle known for a common failure. When that vehicle arrives to a shop exhibiting all the typical symptoms related to this failure, the cause is immediately assumed.

Admittedly, the occurrence of fixing a common failure outweighs the few times one might be blinded by a pattern failure repair approach. At the end of the day, this does equate to more dollars in the bank. But the few times a proper diagnostic approach is missed, it can be costly in time, money and in personal frustration.

One such example is with Honda/Acura vehicles that experience converter clutch shudder and failure. One of the ways the complaint is described is that it begins with a sudden shudder around 45 mph. The shudder feels similar to a quick drive over sleeper lines, otherwise known as rumble strips. As quickly as the rumble feeling came is as quickly as it leaves. This can be caused by degraded fluid or the use of low quality fluid, which can be corrected with the use of the right fluid. But most commonly, this indicates a more serious problem is about to emerge. Left unattended, converter clutch failure will be catastrophic, causing the vehicle to arrive on a hook.

This type of transmission is known to have a problem that allows the converter clutch to drag when in the released position. As the clutch begins to get damaged, it shudders on the apply. For a detailed explanation of the failure, read the article “Extending the life of a Honda converter clutch,” written by Dean Mason and published in the Motor Age April 2014 issue. But briefly speaking, there are problems related to the pressure system affecting proper converter pressures. In time the converter experiences an overheating problem so extreme it turns bluish purple in color. Some of the causes of the problem can be attributed to pump wear, pressure regulator operation, leaking lock-up shift and lock-up control valve bore plugs or a restricted heat exchanger.

ATSG Figure 1

With Honda/Acura converter clutch shudder complaints having the reputation of being likened to the tip of an iceberg where bigger problems are lurking underneath, other possibilities are often overlooked and remain unknown. A quote by Donald Rumsfeld goes like this: “As we know, there are known knowns; there are things we know we know. We also know there are known unknowns; that is to say we know there are some things we do not know. But there are also unknown unknowns — the ones we don’t know we don’t know.”

Dealing with both known unknowns and the unknown unknowns is quite a concept to one’s perceived reality. And in particular, with a Honda/Acura TCC shudder complaint between 45 to 55 miles per hour.

This happened with Donald Holliday from Covington Automotive. Interestingly, the customer had informed the technician that the shudder seems to occur whenever he saw the “ECO” Lamp illuminated. The “ECO” Lamp operation is tied into the i-VTEC Variable Cylinder Management (VCM) System found in V6 engines. The VCM is a strategy that automatically deactivates 1/3 or 1/2 of the cylinders, according to the driving conditions. In other words, if conditions are right, the computer will command the engine to run on four cylinders and then three. This technology provides increased fuel economy, which when activated will inform the driver by illuminating the “ECO” lamp.

ATSG Figure 2

When the vehicle is running on three cylinders, combustion pressure per cylinder also increases. This in turn increases engine vibration. To absorb this vibration they use Active Control Engine mounts (ACM) as seen in Figure 1. These are liquid filled mounts that an Engine Mount Control Unit controls to dampen harmonic vibration during VCM activation (see wiring going to the engine mount actuator inside the mount in Figure 2). As a result, Honda states that a slight vibration in “ECO” Mode is considered normal.

Over time these mounts begin to have issues causing the system to malfunction. Whether an electrical problem arises, or the mount itself has deteriorated, the compromised mount or mounts can transmit a harmonic vibration through the car simulating a converter clutch shudder. The key here is whether or not the shudder occurs when the ECO light is illuminated. If so, this would indicate a failed mount as the cause. If you have time, visit mount — it provides a good visual of a collapsed mount with a Honda Odyssey vehicle.

You may find fluid leaking from the mounts as another clue. You may also find service codes store as the ACM system is capable of storing generated trouble codes. Using a 2008 Honda Pilot 2WD V6-3.5L vehicle, some of the codes that can be pulled are as follows:

  • P0A14 and P0AB6 are front and rear Mount Actuator Circuit Malfunctions
  • P0A15 and P0AB7 are front and rear Mount Actuator Control Circuit Low Current codes
  • P0A16 and P0AB8 are front and rear Mount Actuator Control Circuit Low Current codes
  • P15AB is an Engine Mount Control Unit Power Source Circuit Low Voltage code
  • P15AC and P15AD are Engine Mount Control Unit Internal Circuit Malfunction codes


The way this system works is good to know as a malfunctioning ACM can also generate other codes such as a Cylinder Pause Signal Malfunction codes.

Honda describes the system as follows:

  • The engine mount control system controls the engine mounts electronically. The system consists of the engine mount actuators, the engine mount control unit, and the power train control module (PCM). The engine mount control unit uses the crankshaft and camshaft position sensor outputs (received from the PCM) to estimate engine vibration. The engine mount control unit then sends signals to the engine mount actuators to command the engine mounts to push and pull on the engine to counteract engine vibration. The engine mount control unit monitors the rear engine mount actuator, and when an abnormal condition continues for a set time, the engine mount control unit detects a malfunction and stores a DTC.


For this reason you will encounter Cam Shaft Position Sensor (CMP) and/or Crankshaft Positions Sensor (CKP) codes that could be caused by a failed Engine Mount Control Unit.

To be continued on Part 2 of DON'T BELIEVE EVERYTHING YOU THINK...