Sounds like it could be a bad bushing in a tie rod or control arm or something in the struts. Do you feel a thud anywhere and is it on the left or right side? It could also be the engine mount, but since the gas engine isn't driving the wheels and I'm guessing you hear this in all EV mode. It could also be noises coming from the regen, generator, engine gearing. Can you give more details? What happens if you accelerate, decelerate, accelerate, decelerate, can you make it happen most of the time? Can you figure out what speeds it happens?

 

Happens in either mode as far as I can tell and at very low MPH -- like 1-5 mph when just starting off from a stop. Seems from driver's side front of vehicle. (Speed when stopping I have not pinned down, but seems slow speeds).

 

If you have a floor jack (search for other threads or look at the owners manual to find the jack points - I didn't use scissor jacks as some suggested but used a floor jack that barely reaches a mount point near the back of the engine where the jack bar would only move and inch or so until the car got higher, then I could move the bar more. To avoid damaging anything with metal on metal, I jupigsawed a small wooden disc for my jack). Once the front wheel in question is off the ground grab it with two hands and see if you can wiggle it horizontally or vertically or diagonally. If it has any play whatsoever then it is some bushing. If not, take of the tire and have a look at the brake caliper as suggested by tsquare. Be very careful not to get underneath the car without jack stands (although with the jack under that I'm nor sure where a good place to put jack stands are.).

 

You might want to read this thread from another member.
http://gm-volt.com/forum/showthread.php?43273-Cause-of-quot-Thunk-quot-noise-found-missing-Front-Brake-Caliper-Bolt.-NOT-PSB-12-03-08-001

 

Wow that sounds scary -- not having a bolt in the brake caliper.

I'm stumped. It doesn't seem to happen over bumps etc., like the brake caliper guy, however. Just when starting out from a stop, or slowing to a stop. But then again, who knows. I hope they can figure it out without having to tear the car apart.

If it really is a brake caliper bolt missing, that sure sounds like something to consider for a recall, if it came from the plant like this or worked loose because of a design/install problem.

My last car, a Hyundai Sonata, had a huge recall to replace the engine cradle because the design trapped moisture and they could rust out over time. Some people had the engines drop and even caused crashes and injuries (where were the huge investigations and media hype then against HMA, hmmm......).

 

The click sound is often times the CV joints. Does it make a difference if you are making a turn??

 

Mystery Solved:

The new Chevy dealer I took the Volt to says that the click/thunk noise is from: 1.) The "set screw" for the driver's side brake rotor has sheared off (possibly when a brake job was done?). 2.) Therefore the entire hub assembly needs to be replaced. 3.) Also, the left front axle nut needs to be retightened(?). These things he said caused the rotor and axle to move improperly, which caused the noise. GM, thank Gd, is going to help me with out-of-warranty assistance for those two problems, plus the fraying driver's seatbelt and the cracking plastic fuel filler assembly. I will have to pay 50% of the total or $600 for the hub, seatbelt and fuel door, and $210 for the diagnostic time, axle nut re-torquing, and labor to update the car's operating software.

Further, the air filter was totally clogged and the fuel/throttle system is severely gummed up and needs cleaning, for $159.95, which I will have to cover all of.

He said they checked the trans fluid and that is so-so and can wait a brief bit. The brake fluid he said they tested for 'elevated copper levels' and that it seemed fine, so doesn't need flushing yet.

I called the original dealer and demanded to know how in the world their Volt tech could have missed so many serious problems with the car during the inspection I paid for, and that I was worried about his competence about checking the state of the Voltec system and the battery, which I was most concerned about. So they have apologized and agreed to give me the trans fluid flush for free, credit the cost of the inspection fee I paid for towards future repairs, detail the car, and, finally, sell me the new tires at cost and waive the installation and other charges. So that makes things a bit better, at least.

All very interesting.....

 

Now I'm getting this click, too. Other threads here,
http://gm-volt.com/forum/showthread.php?120705-Thunk-Click-sound-not-brakes&highlight=click
and here,
http://gm-volt.com/forum/showthread...read.php?101145-Drivetrain-click-need-confirmation-please/page2&highlight=click

Took it to dealer, who tightened the axle nut, in front. Now, it is back. Getting slowly louder. I can put the car on the lift and check set screws, but think that is a cover for a lash problem in the axle assembly. Perhaps the hub develops play. This falls under drivetrain, and would be covered in my case, so long as the dealer's service department finds and addresses the problem correctly, before warranty expires.

What is the torque spec for the Volt's front axle nuts?

 

Once you get those things under control you should have a long lasting, high MPG vehicle. And at least you are getting some help towards getting those items repaired. Better than finding it out 6 months and 5,000 miles from now or worse breaking down.

 

Sounds like your car had, at best, incompetent maintenance and at worst, no maintenance. Enjoy your car. It's a good one.

 

So...
Do you have any idea where the brake job was done and why? With the regen braking, the hydraulic system is very lightly used. I am very surprised a brake job was required on a 2012. How many miles are on the car?

 

No clue. The car was a fleet vehicle from General Electric. That I'm 99% certain of. So I thought this will be perfect because as a fleet vehicle, they would take very good care of it and give it good maintenance.... Um, apparently not. The Chevy dealer mechanic told me that generally no, fleets do the bare minimum, like oil changes, but for other things generally they fail. He said he thought, from the way it looked, the air filter may have never been changed at all. Ughhh that was not what I wanted to hear. Well, I guess I better get the car in good shape now, and do all the preventative stuff while I can, before things really big fail. I am very grateful to GM for stepping in and helping with part of the repairs, out of warranty. That's above and beyond good and I will not forget it. They did something similar years ago with my grandfather's (yes) Oldsmobile, when the transmission failed.

And re the possible brake job (still not sure whether it was a brake job that caused the sheared screw or a part defect...) the car has 94k. GE drove this car a lot. At least still has some warranty which is what I insisted on - there are other ones out there being listed with mileage +100k and those I was more hesitant over because of battery warranty. (Is there anything specific I should ask the new dealer to check, now, while the car is still partially warrantied? Something major that can go bad at this point? EV system? Drivetrain? -- The first Chevy dealer supposedly checked everything, before I bought the car, and said all was fine, but I don't have any faith in their mechanic's competence anymore, since he missed so much.)

 

That is a lot of miles. I agree that GM is going above and beyond in helping out with the repairs. Kudos to them.

On the plus side, given the number of miles and the reported state of the air filter, throttle assy and fuel filler neck, it appears that this car was driven largely in ER mode. So the ICE and generator may have more use than average, but the high voltage battery likely has fewer charge cycles than average. Probably been carried around for the past 2 years happily sitting at 30% SOC. If your wife's driving pattern uses primarily electric miles then I would have little worries about the condition and life expectancy of the battery or the car in general.