[PearlWhitePilot2016]

Makes me wonder if there is something wrong with your AT transfer components bc AWD engages briefly when you either turn or start from dead stop. Not saying there is nothing wrong with the AT but maybe good to do a quick inspection of the transfer case, propeller shaft and any lingages along those lines. Also check transfer case w/ fluid level (and differential fluid). May help to narrow this to AT altoghether by eliminating AWD components.

 

[undivide]

have you done a drain and fill on your rear axle with the vtm4 fluid (honda brand)
I picked up a jug on amazon a year ago for 38 usd, it is now 39 it seems. not sure what a local dealer charges.
I remember watching a couple videos that describe weird sounds going away after a fresh fluid change.

 

[jimmaki2000]

Makes me wonder if there is something wrong with your AT transfer components bc AWD engages briefly when you either turn or start from dead stop. Not saying there is nothing wrong with the AT but maybe good to do a quick inspection of the transfer case, propeller shaft and any lingages along those lines. Also check transfer case w/ fluid level (and differential fluid). May help to narrow this to AT altoghether by eliminating AWD components.

During the long search to solve this problem I have changed (drained and refilled) the ATF five times with Valvoline Max Life pure synthetic, in addition to the rear differential and transfer case using OEM Honda fluids. Turning off traction control seems to have done the trick. If there's a way to turn off AWD and turn traction control back on, I'd interested in seeing what kind of difference that would make, if any.

My thinking is that in a turn from dead stop, the traction control may be misinterpreting the faster turning outer turn radius wheels as slipping and applies brakes and reduces power to them to stop the slipping. Once the turn is complete the wheels on both inner and outer radii are turning the same speed so the system relinqueshes control and that's why the shudder stops once the turn is complete. I hadn't considered the VTM4. Is there a way to switch it off like I can the traction control?

 

[jimmaki2000]

have you done a drain and fill on your rear axle with the vtm4 fluid (honda brand)
I picked up a jug on amazon a year ago for 38 usd, it is now 39 it seems. not sure what a local dealer charges.
I remember watching a couple videos that describe weird sounds going away after a fresh fluid change.

Yes I changed the rear axel and transfer case with Honda designated OEM fluids. Yes, the Honda VTM-4 fluid is close to $40 by the time it arrives at my front door.

 

[PearlWhitePilot2016]

During the long search to solve this problem I have changed (drained and refilled) the ATF five times with Valvoline Max Life pure synthetic, in addition to the rear differential and transfer case using OEM Honda fluids. Turning off traction control seems to have done the trick. If there's a way to turn off AWD and turn traction control back on, I'd interested in seeing what kind of difference that would make, if any.

My thinking is that in a turn from dead stop, the traction control may be misinterpreting the faster turning outer turn radius wheels as slipping and applies brakes and reduces power to them to stop the slipping. Once the turn is complete the wheels on both inner and outer radii are turning the same speed so the system relinqueshes control and that's why the shudder stops once the turn is complete. I hadn't considered the VTM4. Is there a way to switch it off like I can the traction control?

Good to know all fluids have been checked/replaced. The fact that ATF changes does help short while only confuses me. Anyways, I took a VSA system and VTM4 electrical diagrams, and following your reasoning, i traced the VSA modulator control unit and finding there are 4 wheel speed sensors that feed into the control unit to modulate the wheel spin. I suppose if anyone of them is defective (not sure why it would be), you may have incorrect VSA command. Also looking at the VTM4 circuit, there are 2 clutch electro magnetic oils in the differential so if one of them has failed you could have potentially improper/inbalanced operation. I am not a big fan of taking apart the differential as a DYIer as I don't like to crawl on my back but you may check and see if there is anything obvious on wheel speed sensors. BTW, which side is giving you the shudder? LF LR RF RR?

 

[brybo86]

I had the exact same shudder/vibration/chatter when starting from a dead stop and turning at the same time. But not when starting in a straight line...

Issue fixed by drain/ fill of rear diff

 

[undivide]

time to convert to FWD and just yank the rear axle shafts !

 

[cintocrunch]

Is there a way to switch it off like I can the traction control?

I think you can just pull the fuse and it will disable the rear diff.

 

[jimmaki2000]

Good to know all fluids have been checked/replaced. The fact that ATF changes does help short while only confuses me. Anyways, I took a VSA system and VTM4 electrical diagrams, and following your reasoning, i traced the VSA modulator control unit and finding there are 4 wheel speed sensors that feed into the control unit to modulate the wheel spin. I suppose if anyone of them is defective (not sure why it would be), you may have incorrect VSA command. Also looking at the VTM4 circuit, there are 2 clutch electro magnetic oils in the differential so if one of them has failed you could have potentially improper/inbalanced operation. I am not a big fan of taking apart the differential as a DYIer as I don't like to crawl on my back but you may check and see if there is anything obvious on wheel speed sensors. BTW, which side is giving you the shudder? LF LR RF RR?

The shudder is felt in the seat and center armrest. It only lasts a few seconds so it is difficult to isolate to a corner of the car.

I didn't see any obvious problems with the speed sensors like loose or broken wires. My guess is if one or more speed sensors were bad that the ABS or brake light or VSA light would come on. ABS seems to be working when I stand on the brakes and try to lock them up.

No oil leaks, stray wires or anything remarkable with a cursory look at the rear differential. If a clutch or coil were bad, I'd expect to hear noises from the rear end when doing the parking lot figure-8 test. It seems perfectly quiet and there is no noticeable vibration.

My theory about the outer turning radius wheel looking like it is slipping to the VSA system doesn't seem to hold water if the Honda engineers were smart enough to have the system monitoring the turn angle sensor so the ECU would know when the vehicle is making and finishing a turn. But then again, if the turn angle sensor were bad or out of cal, I would expect a code or light or wierdness in the steering. None such.

So why turning off the stability control appears to fix the problem, I have no other theories. (providing the turn angle sensor is in the mix)

And like you, it is confusing to me why changing the transmission fluid five times alleviates the problem, albiet temporarily. (a few thousand miles) So far the turn off stability control appears to be a longer term "fix." (fingers crossed)

To be clear, I'm not suggesting anyone else turn off their stability control. I run soft sticky Michelins so no slipping in rain and non-existent snow in Florida.

 

[jimmaki2000]

I think you can just pull the fuse and it will disable the rear diff.

But will that disable the VSA system too? I'm guessing the stability control uses the ABS to pulse the slipping wheel in an effort to stop the slip. (by "slip" I mean the ECU misinterpreting the outer radius wheel turning faster than the inner radius wheel during a turn as slipping)

 

[jimmaki2000]

I had the exact same shudder/vibration/chatter when starting from a dead stop and turning at the same time. But not when starting in a straight line...

Issue fixed by drain/ fill of rear diff

I had the exact same shudder/vibration/chatter when starting from a dead stop and turning at the same time. But not when starting in a straight line...

Issue fixed by drain/ fill of rear diff

Same here but the drain and refill "cure" only lasted about 3,000 miles and then started to gradually come back. Turning off stability control seems to have solved the problem and the car accerlerates faster and smoother from a dead stop both turning and in strightaways.

 

[jimmaki2000]

time to convert to FWD and just yank the rear axle shafts !

Yeah, I tried that but the rear wheels fell off.

 

[dr bob]

Consider removing the driveshaft to try and isolate the cause of the vibration.

Disabling VSA also disables the initial RWD engagement on launch. Since you report that the ATF flushes offer some temporary relief, and the vibration is most prominent in the seat and center console, I suggest that the problem is related to the driveshaft itself and the carrier bearing.

Have you had the PCM updated? Early vibration issues as you describe were treated to a PCM update that softens the initial torque application to the rear wheels. It helped some for some owners/cars. The update is part of a TSB for low-speed vibration, and that treatment included a driveshaft replacement. There's a sticky thread at the top of the forum that included details of the process. Bottom line though is that if removing the driveshaft eliminates the vibration symptom you describe, going through all the steps in that 2015 TSB including PCM flash and a new driveshaft would be the logical next steps.

TL;DR
For those playing along at home, the VSA system uses selective torque application to rear wheels (via the electric differential clutches) along with selective brake application to help steer the car when slippage is detected, plus for low-speed launch. The TSB addresses the issues with driveshaft "windup" and vibration as that torque is applied, plus when the VCM system causes rapid driveshaft windup and release just in normal driving. The transmission flush with Max Life fluid allows the torque converter to better deal with the torque pulses, mostly by delivering more to the front wheels. Disabling VCM eliminates that part of the driveshaft issue, but leaves the initial application at launch intact. Regular service of the rear differential is key to getting the right application (and release...) of the wheel clutches.

Fuse 2 (20A) in the Aux Under-Hood Fuse and Relay Panel supplies power to the VTM-4 clutches via the VTM-4 relay in that same panel, then via the VTM-4 control unit itself. Control Power for the VTM-4 control unit is supplied through Fuse 1 (7.5A) in the Under-Dash Fuse and Relay box. Removing the control power fuse disables the VTM-4 dash controls and indicators, and also prevents the VTM-4 relay from closing to power the VTM-4 clutches in the rear differential. Removing this fuse may cause a trouble code.

 

[jimmaki2000]

Consider removing the driveshaft to try and isolate the cause of the vibration.

Disabling VSA also disables the initial RWD engagement on launch. Since you report that the ATF flushes offer some temporary relief, and the vibration is most prominent in the seat and center console, I suggest that the problem is related to the driveshaft itself and the carrier bearing.

Have you had the PCM updated? Early vibration issues as you describe were treated to a PCM update that softens the initial torque application to the rear wheels. It helped some for some owners/cars. The update is part of a TSB for low-speed vibration, and that treatment included a driveshaft replacement. There's a sticky thread at the top of the forum that included details of the process. Bottom line though is that if removing the driveshaft eliminates the vibration symptom you describe, going through all the steps in that 2015 TSB including PCM flash and a new driveshaft would be the logical next steps.

TL;DR
For those playing along at home, the VSA system uses selective torque application to rear wheels (via the electric differential clutches) along with selective brake application to help steer the car when slippage is detected, plus for low-speed launch. The TSB addresses the issues with driveshaft "windup" and vibration as that torque is applied, plus when the VCM system causes rapid driveshaft windup and release just in normal driving. The transmission flush with Max Life fluid allows the torque converter to better deal with the torque pulses, mostly by delivering more to the front wheels. Disabling VCM eliminates that part of the driveshaft issue, but leaves the initial application at launch intact. Regular service of the rear differential is key to getting the right application (and release...) of the wheel clutches.

Fuse 2 (20A) in the Aux Under-Hood Fuse and Relay Panel supplies power to the VTM-4 clutches via the VTM-4 relay in that same panel, then via the VTM-4 control unit itself. Control Power for the VTM-4 control unit is supplied through Fuse 1 (7.5A) in the Under-Dash Fuse and Relay box. Removing the control power fuse disables the VTM-4 dash controls and indicators, and also prevents the VTM-4 relay from closing to power the VTM-4 clutches in the rear differential. Removing this fuse may cause a trouble code.

The dealer updated the PCM and informed me the vehicle already had the new driveshaft based on a purple mark on the center bearing shield. The shaft universal joint bearings and splines were checked for damage, binding or excessive play. There was no improvement or even difference in the shudder during a turn and shortly after a turn after this service. Returning with the same complaint I was told a rebuilt transmission might fix the problem or could make it worse. Since there were no codes, I would have to bear the full cost.

I went back with the the TSB you mentioned and all steps were done. They even took it for a test drive with the drive shaft detached. Also, some sort of live data test was run on the transmission, the name of which I don't remember but it came back "normal" as did all other tests they ran. I finally got the "This is normal, learn to live with it" speech.

Since the vibration appears to be gone and acceleration from a dead stop seems to be livelier with the VSA off, I am going to try disabling the VTM-4 clutches and leaving the VSA on, unless it comes up off with the VTM-4 disabled.

Can you tell, or do you know, if the steering angle sensor plays any part in letting the ECU and VSA know that the vehicle is in a turn so a difference between inner and outer radii wheel speeds is not indicative of outer wheels slipping? (so no reduction in power and braking of the outer wheels is needed)

Thanks for clarifying that the MaxLife just allows the TC to deal with the pulses better and not eliminate them. That part had me stumped.

I'll report back after another D&R and mechanic check of the rear differential as well as also disabling VTM-4 if nothing turns up back there.

Thanks for taking an interest. This has been more intellectual curiosity torture than a physical one since the shudder only lasts a few seconds accelerating out of a turn after a dead stop. It used to shudder more coming out of a right turn than a left turn. The bigger radius of the left turn is what led me to think the difference between inner an outer wheel speeds less and that the right turn with tighter radii was fooling the VSA the outer wheels were spinning and the shudder was the ABS tapping the brakes on the outer wheels.

I don't think it's my imagination but with the VSA off from a dead stop, acceleration seems much livelier, like the engine power isn't being restrained and no braking is taking place.

 

[jimmaki2000]

I had the exact same shudder/vibration/chatter when starting from a dead stop and turning at the same time. But not when starting in a straight line...

Issue fixed by drain/ fill of rear diff

Thanks, it's good to know I'm not the only one experiencing this problem that Honda "never heard of before I reported it." How long ago, or miles ago, did you do the D&R? How many miles did the drained ATF have on it? And did you just do one D&R?

 

[undivide]

if the VSA was being activated because of a loss of traction then wouldn't the dash light flicker on to indicate? it is very amazing that the only thing that apparently from what you say stops the issue is turning VSA off by hitting the button. I would almost think the issue would be something mechanical but then again electrical issues are funny to track down especially when they throw no codes or warning lights. VSA and VTM4 systems use input from your wheel speed sensors to make decisions about what to do. maybe take the sensors out and clean them and the tone ring ?

 

[AVC]

Thanks for clarifying that the MaxLife just allows the TC to deal with the pulses better and not eliminate them. That part had me stumped..

Yeah, thinking I'd like some further technical clarification from @dr bob on exactly how VML might accomplish that torque preference to the front axles.... 🤷‍♂️

Spitballing...

@jimmaki2000 did you or anyone else do a complete drain and fill of the VTM diff? That diff fluid is famous for absorbing water and causing clutch chatter in the diff. Can't you also disable the rear diff by unpugging the electrical connector at the diff? (my '03 was AWD, so I'm stretching my memory a bit).

Did anyone check if one of the rear wheel speed sensors is providing a marginal signal at low speeds, confusing the PCM re: torque management on turns?

 

[brybo86]

Please drain and fill rear diff with Honda vtm4 fluid, don't rush it.
Fill it until it leaks then spin the wheels abit and top it off again. Then grab a beer and top it off again.

I bet your diff fluid is either incorrect fluid, low fluid level , dirty fluid, or all of the above.

Did you do the diff service yourself or someone else?

Was it level when performed?

 

[dr bob]

Taking the comments somewhat in order:

-- Even though the driveshaft has been replaced, removing the driveshaft again is a diagnostic step. If the symptom (vibration felt in the center console and front seat) goes away, you've narrowed the possible causes quite a bit. Diagnosis is a divide-divide-divide effort to progressively narrow the possible-causes list to one.

-- Smoother torque transfer through the converter doesn't actually increase total torque to the front wheels. It does allow more to flow to the front, since the VTM (rear) is not reacting to the pulses as faults. There are large rubber drive dampers at each rear corner between the ABS sensors and the road, disguised as tires, so any changes in the way the sensors read axle position offers a VTM "correction". That means activating a differential clutch, risking a bigger 'windup'. Goes back to isolating the rear drive by removing the driveshaft, then again by pulling the VTM fuse to prevent the clutches from activating at all.

In general, "I've done everything and still have a symptom" means you haven't really done everything, or one of those "everythings" was not done correctly. In other similar cars I play with, the rubber damper in the center bearing carrier effectively changes density with age and heat. The goal is to absorb vibration well enough to prevent harmonic oscillation in that driveshaft.

Taking the driveshaft out allows you to investigate possible front suspension movement, something that's certainly more possible with some steering lock when launching from a stop. Lower control arm compliance and plain inner bushings in great shape? Got more than 75-100k on the car? Control arm replacement might be a good diagnostic step if you get any vibration with the driveshaft removed.

Disabling VSA disables the electronic throttle management component, something that might offer a perception of improved performance. Since the OP reports this symptom, focus should remain on torque delivery and how pulses in torque can be interpreted as wheel slip by the system. Normally VSA would respond by adding rear drive torque via VTM, while it gently reduces total torque delivery by moderating actual engine drive-by-wire throttle position.


Perhaps the important things to consider include how the system works as a network, a system, a matrix of sensors and mechanical bits that constantly look for something going wrong, and then correct for that. Is there really something wrong, or are we just feeling the corrections. Separating the number of possibilities is the easiest way to eventually focus on a cause.