Jake Brake Noise

Long time member, but first time asking a question. My 2021 Sport has developed a “noise” similar to Jake Brake noise on a big truck. Only hear the noise when slowing down, engine warm and very light brake application. No sound after I start accelerating again. I am not a mechanic, but the noise is driving me crazy. Thanks for any input before I make an appointment with my dealer.

 

If it's the same (very light throaty) noise I hear on mine under those same conditions (coasting downhill/slightly on the brake), then it's probably normal (it definitely is not the 2000 dB racket big rigs make going down a long rural grade lol... If that's the case on yours, you got something quite serious going on). The noise continues even after fully letting off the brake until I give it light throttle.

To me it sounds like the EFI cutting off all fuel at the injectors when it is not needed to ever-so-slightly increase engine braking / MPG (someone else can confirm). I hadn't noticed the noise on mine until I correlated it to the sudden increase in drag while coasting downhill that at certain grades means I have to slightly apply the throttle at times to overcome it. Just another one of those "modern vehicle things" that we all have to put up with (drive-by-wire throttle lag is another).

Maybe it can be turned off /disabled with a tune?

 

I saw a post here that said it had to do with the torque converter(lock up) and was normal.

 

My 2020 does it as well. I animate along with it when it makes he jake noise.

 

I worked at the GM Technician Assistance Center (TAC), the call center where a dealership tech who needed help (couldn't figure out what to do) could get that help, back in 2016.

At GM what you're talking about is called Deceleration Fuel Cut Off (DFCO), and your explanation of how it works is spot-on. It CAN cause a change in exhaust note, notably when it kicks on and off. The GM trucks had a spring loaded flapper valve in the exhaust between the cats and the muffler to increase the back pressure that gave us fits because they could cause a slight rattle at times.

OP: try to find a downhill grade where you can let the truck coast and make the noise happen every time, preferably without any brake application. Then crack the throttle to raise the idle just slightly and see if the noise goes away. Remember, if you can make it happen every time, and show the mechanic how to make it happen, you're MUCH more likely to get a repair than saying sometimes when I...

 

Sorry for late response, but thanks for the possible causes of this problem. I think I’ll try to record the sound on my phone and then contact local service team. Thanks again!

 

Money on loose skid plate

 

Away! Good suggestion. I was hit by red light runner a few years ago and driver side front damaged. Many of the suspension parts replaced, and Taco ran perfect for a year. Maybe I’ll crawl under and check bolts in the area!

 

These engines sound like crap, LOL. They make every noise possible when accelerating, decelerating, idling, whatever. You truck is probably fine.

 

OR and PRO do it but not sports