'Vibration" at stop lights?

[Bob G]

So I noticed quite a while ago that there was a vibration sound that sounded like it was coming from behind the center display/radio unit when I would come to a stop at a light or stop sign. I thought something was loose in the dash and that at a stop the right vibration/frequency happened and it would resonate so I would hear it. (Even the wife has noticed it) I have played a bit with it and have determined that I can very consistently make it go away by shifting the transmission to Neutral. It almost seems like the transmission doesn't want to 'slip' when sitting at an idle with the transmission in "D". I have also noticed that if the truck is sitting at an idle in the driveway (level/no slope) and I shift in into "D" and take my foot off the brake, the truck begins moving without touching the accelerator pedal.

Is this normal/expected behavior for the beast as this is my first Ram/Cummins? Is this indicative of a problem with the transmission adjustments? I still have a few months left on my warranty so was wondering if this was something that should be brought up? Truck goes into the closest dealer next week for a P20B9 Code (open circuit in the control system for the reductant heater "A")

Thanks for any comments/suggestions

Later,

Bob

 

[Grumpy8811]

my truck drives itself down the road at idle in gear, I always thought that was normal as everything else I own is the same way..
as far as the vibration goes it is probably a harmonics thing where something in the truck is slightly loose and buzzing a bit , so maybe get someone to hold foot on brake while in gear and you go look under the hood and under the truck too.

sounds travel thru a vehicle and may be coming from somewhere far away from where you think they are coming.

 

[Bob G]

my truck drives itself down the road at idle in gear, I always thought that was normal as everything else I own is the same way..
as far as the vibration goes it is probably a harmonics thing where something in the truck is slightly loose and buzzing a bit , so maybe get someone to hold foot on brake while in gear and you go look under the hood and under the truck too.

sounds travel thru a vehicle and may be coming from somewhere far away from where you think they are coming.

It definitely seems like it is coming from the transmission as I can "turn it off and back on" by shifting to Neutral and back to Drive. It does seem to be less when you turn it back on by shifting to Drive, but it goes away completely by shifting to Neutral. I have almost developed the habit of shifting to Neutral when coming up to a light.

 

[Grumpy8811]

It definitely seems like it is coming from the transmission as I can "turn it off and back on" by shifting to Neutral and back to Drive. It does seem to be less when you turn it back on by shifting to Drive, but it goes away completely by shifting to Neutral. I have almost developed the habit of shifting to Neutral when coming up to a light.

neutral is unloaded for lack of a better word, whereas drive the clutches are engaged.. and there is more load on the engine..
I don't have a direct answer what it could be, but it could be anything from a bad motor mount or loose component that only vibrates at idle to something wrong in the transmission.. This sort of thing can be hard to diagnose, but a first step is to let it idle in gear and search around the vehicle and see if you can pinpoint the source.

 

[BigUglyRacing]

Not sure this is your issue. I just ran into a similar thing just a few days ago on my 18. I started hearing a similar sound to what you describe (mostly when the motor was cold and in drive not moving). Tracked it back to the plastic shield that is on the power steering fluid reservoir. It would vibrate but could not be heard from outside till i popped the hood. And bingo there it was. Just moved it around a bit till it stopped.

 

[mpaulson]

Some have mentioned a loose retainer clip by the brake master cylinder under the hood too that will vibrate and transmit sound into the cab.

 

[bigblock_doc]

When dealer replaced my cp4 pump it came with a new power steering hose. It was touching the master cylinder.
Gave it a little bend and noise went away.