Humming noise while driving

The noise is not enough for a diagnosis:

• Is the pitch speed related?
• Does it stay if the car is shifted into "N"?

The hum is associated with MG2 stator winding short which only gets worse. For a proper diagnosis:

• Is MG2 temperature > MG1 temperature? (Use a Prius aware scanner)
• Does MG2 temperature rise sharply as soon as the car moves?
• Does the transaxle oil smell and look burnt? (sample from the fill hole)

There are two known repair techniques, swap with a salvage transaxle or rebuild by replacing MG2 stator assembly. It is a major repair, easily $1,000, but once done, you've got a car that can achieve 50 MPG. Use the "search" function for "MG2" to see what we know.

Bob Wilson

 

How's ur alignment & tires? These can cause a humming noise

 

Have you had the car long enough to say you've got a new hum that wasn't there before? Is it getting more noticeable?

When mine hummed it turned out to be a wheel bearing. Do you have a tuner (or a good sense of pitch) to be able to say what pitch the hum is at what road speed? I posted some details about the sound from my wheel bearing. The other possible hum source to try to check or rule out is the motor-generator in the transaxle (much more expensive) and it should sound different. You will also see notes in that other thread about how to measure the motor-generator temperature, another way to check whether that is the problem.

Hope this helps,
-Chap

 

In that case you might have a new kind of hum we're not as familiar with. Both the wheel bearing (easy fix) and tranny stator (expensive) will change in pitch according to your driving speed, so if yours does not, you probably aren't hearing either of those.

-Chap

 

If the hum is constant.. double check it isn't coming from behind the rear passenger seat on the driver side. There is an electric fan that can be loud and constant noise if the traction battery is overheating.

There is a coolant pump constant noise under the hood that will be on whenever the car is in READY, but you would notice that sitting in a driveway. Stick your head under the hood when car is in READY, coolant pump is in the front right corner.

Does the ICE ever shut off when you put it in Park?

The hum is always there? when ICE is running? only over 20mph? Always same sound when car is moving???? MG2 and wheel bearing all depend on the speed you are going.

 

That's good news for u

 

Just sharing some recent insights:

--- In [email protected], hobbit@... wrote:
>
> I finally wrote up the bad-wheel-bearing incident from December; y'all have
> seen the gist of the leading text here already but the detailed shots of
> the bearing parts are toward the end.
>
> Wheel bearing
>
> On one hand a PITA, but on the other I have to admire what those little
> suckers can go through and survive.
>

Found an even better article:

"How to Determine Bearing System Life" by Erwin V. Zaretsky


How to Determine Bearing System Life



Hobbit's bearing photos are dead on for 'spall' damage.


This article goes on to illustrate two mechanisms and includes a probability table:

27% - corrsion pitting
20% - debris denting/contamination
17% - dimensional
17% - Other
7% - handling
6% - wear
3% - cage wear
3% - fatigue

I was especially interested because the article discusses the L10 (aka., probability of 10% failure.) This is not the first wheel bearing failure. My thinking is researching all Prius wheel bearing failures and the accumulated miles could be treated as the L10 wear miles. Certainly not perfect, it may lead to a 'rule of thumb' on the wheel bearing, expected life.

We might take a 'cheat' and consider each car to have exhibited the L25 (one of four wheel) failure rate. But this could lead to a too conservative rate.

So why is this useful?

If we have an expected 'useful life' for the bearings with some basis of estimate, we can proactively replace the bearings at a time and place of our choosing ... possibly shopping around for a better deal. Then not worry about it for a long, long time.

Regardless, it is an interesting article.

Bob Wilson