So I've put on about 600 miles on my '13 Tahoe Hybrid and overall I remain highly satisfied with my purchase decision. Kudos, once again, to the engineers who put this rig together.

Now what I'd like to understand is just get an idea of what's normal and what's not. I love the quiet operation, but today, while in stop and go traffic for about 15 minutes or so, the engine didn't go into autostop. Perhaps it was recharging the battery? No real idea just guesses here, but while the engine was running while stopped with brakes on, I heard this faint rattling/buzzing noise under the hood that's typically absent. When I lightly press the throttle, the noise would immediately go away. Get off throttle and the light rattling is back.

After a minute or two, the autostop function would resume and back to library quiet operation. 5-10 minutes or so later, when the engine wouldn't go into autostop even at a stop, I'd hear that faint noise, again.

Is this normal? Anything else I should consider normal so I don't bug my Chevy service guys about it? I can't imagine it'd be simple to reproduce the noise.

Thanks!

 

Next time you hear the faint rattle/buzzing quit, pump the brake pedal a few times to start the brake pump up. See if that is it.

There may be something touching the body or frame that should not be. Trans oil cooler lines can be one.

The air conditioning compressor also can make a buzzing sound. AC compressor right front under hood. Brake pump under your driver's seat under floor. Trans cooler lines run forward on driver's side of enine.

 

I'll see if it happens, again. I'm betting it will. Kinda disappointing, if in fact the noise isn't normal, for a brand new car to have such not-normal noises. It does sound like a powered motor making a high frequency buzzing noise. And it only happened when the ride wouldn't go into autostop mode when it does so most of the time I've driven the thing.

It is faint enough that I can't hear it if I have the radio on. Thank you.

P.S. AC was never on

 

It may be "normal" there are more pumps and motors in the hybrid. Autostop is a fussy thing sometimes. The transmission, engine, and HV battery need to be within temperature and charge ranges. Shifter is in D not M?

 

Doing some reading ahead of time (many of your posts to be honest - good stuff), I was expecting autostop to intermittently not do its thing after stop-and-go. It was just a noise I hadn't heard before and I like to avoid leaving my car at the dealership or any other vendor, thus my participation here. It does give me a pause to wonder how the drivetrain will function in more extreme weather conditions like 80 degrees, AC on blast, in the thick of freeway traffic. I'm sure the GM brains worked out all the kinks.

Shifter in D. Drivetrain in auto, though in the dry I leave it in 2wd. AC off. Heater set to 70 degrees. Very ordinary commute. Low 50s outside and raining.

 

Low 50s and rain... sounds like home to me. Don't get too worried about maximizing your autostop electric operation. It's the total hybrid system of reclaiming kinetic energy during re-generative braking and easy acceleration to allow some of that energy you got back from the previous stop that has a big effect. Now in heavy grid lock maximizing engine off will put you at a big advantage over the guy next to you burinng gas and making a hot torque converter.

Long easy stops with that needle in that EFF gage not out of the green will maximize the Joules recovered in stopping. Real hard stops of short duration will regenerate maximum power kW but it is the time at power that fills the battery up. So a long 25 kw stop will help more than a short 30 kw. Braking hard enough to go outside the green zone will just make hotter brake pads.

I would love to see a hybrid rodeo where stopping from a speed and using a thermal image on brake rotors was one contest. Coolest brakes win.

EV bracket drag racing too. First one across finish wins... but... if you start your engine you braek out. You would need some serious pedal control there.

Back to best fuel economy. V4 is your friend. The hybrid has a 6.0 so a 3.0 V4. More V4 than comparable Tahoe with 5.3. Hower, that doesn't explain all of it. The non hybrid can't call on another 15 horse power on a small hill on I-80 in Iowa from the battery to stay in V4. Another feature you have is the camshaft phaser. No not Captain Kirk's phaser, a device to change cam timing on the running engine.

On decelerations and long down hill such as a pass or gap on interstate, your hybrid will go to V4, roll the phaser to a minimal air flow position, and shut off the fuel. The minimal air flow keeps the catalytic converters hot and does not over oxegenate them. Your engine is turning but you may also be charging. The hybrid can and does use some electric power in these down-hill easy pedal cases to keep the engine off. So V4 can be up to 50% of your total freeway operation. The hybrid is generating when it can and using that power when it can. That is the real beauty of the well integrated hybrid. Maximum EV distance is a neat parlor trick but the drive from Chicago to Omaha at posted speed and 22 mpg is impressive in a 3 ton sport brutility vehicle.

3 tons times 22 mpg = 66 ton-miles-per-gallon. Now take anybody elses hybrid and multiply tons by "real" in-the -wild mpg and see how that number holds up.

It should impress. Safe travels.

 

Fascinating stuff. I actually don't think too much on what's doing what in the drivetrain. I mas o menos enjoy the smoother, quieter driving experience which is totally anti everything I've done in the past with my cars. I spent money to make the gas engine louder and still enjoy this aspect of ownership to this day.

But I'd never mod at the sacrifice of reliability. If I hadn't run into this forum and pinged some hybrid folks about ther servicing and maintenance records (anecdotally as reliable as its all combustion engine counterparts), I would not give any hybrid let alone an American hybrid the wire transfer time of day. Innovation and new tech means very little to my auto ownership experience if the thing isn't dependable. Especially a utility mobile like the tahoe.

So these extra noises and such are important to me to know it is normal operation. I still don't know. It is loud enough to make the hybrid look bad in front of passengers. Wtf is that buzzing noise? Oh just a hybrid quirk.

I don't like that.

 

normal noises,no worries here. a very reliable rig. the hybrid is so quiet, that when my new range rover sport is idling with a/c ON, I can't believe how noisy it is.

 

Haha evois. Funny you mention the rr. I had the 510hp range and while I enjoyed its grunt and luxury, I got rid of it as I didn't trust its getting me to 60k with peace of mind. Nice rig but crazy how the sport model tips scales at nearly 6k pounds for a smallish mid sized SUV!

Hope the tahoe ends up being as bulletproof as the Toyota 4runner I had a few yrs ago. Bulletproof. The 2uzfe engine is awesome. Downside is mpg. Guzzles premium. Got tired of it.