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2012 Silverado lunges forward while braking to a stop #4461226
07/16/17 08:53 PM
07/16/17 08:53 PM
Joined: Jul 2017
Posts: 55
In
SquirrelMan Offline OP
SquirrelMan  Offline OP

Joined: Jul 2017
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In
When I brake, it seems to really lunge forward. I can only describe it as aggressive downshifting? I have been advised by a fellow Silverado owner to turn off the Active Fuel Management with Flashpaq? I would love to hear what some of you guys have to say on this. It's a 1/2 ton crew cab 5.3L 4 speed automatic. 2012. Thanks

Re: 2012 Silverado lunges forward while braking to a stop [Re: SquirrelMan] #4461230
07/16/17 08:58 PM
07/16/17 08:58 PM
Joined: Aug 2010
Posts: 12,915
Northern Kentucky
901Memphis Offline
901Memphis  Offline

Joined: Aug 2010
Posts: 12,915
Northern Kentucky
Nearly impossible to diagnose across web with the limited info we have


2012 Chevy Cruze LT 1.4T - 59k - Edge 0w30 SL + Mahle OX401D
2002 Buick Century 144k - Built 4T65e(Maxlife) - GTX 5w30 + Fram XG3980
Re: 2012 Silverado lunges forward while braking to a stop [Re: SquirrelMan] #4461244
07/16/17 09:22 PM
07/16/17 09:22 PM
Joined: Jul 2017
Posts: 55
In
SquirrelMan Offline OP
SquirrelMan  Offline OP

Joined: Jul 2017
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In
Other forum discussions I have found describe it as "lurching" forward. Happens as transmission downshifts.

Re: 2012 Silverado lunges forward while braking to a stop [Re: SquirrelMan] #4461246
07/16/17 09:23 PM
07/16/17 09:23 PM
Joined: Aug 2013
Posts: 62
VA
mrgrim Offline
mrgrim  Offline

Joined: Aug 2013
Posts: 62
VA
Just my random experience: last year my passenger car experienced a lounge forward per se when I was almost to a full stop. It only happened once, but I checked it out the next day and discovered that my brake fluid had gotten really dirty, and probably contaminated due to the extremely humid summer and stop-and-go tunnel traffic I have to go through. I'm thinking the hydraulic pressure didn't force the brake pads to catch and hold, so I did a brake flush and haven't had that issue again. Given the fact that we're going through another humid summer, I'll probably take a precaution and flush the lines again during my next tire rotation.

Re: 2012 Silverado lunges forward while braking to a stop [Re: SquirrelMan] #4461276
07/16/17 09:57 PM
07/16/17 09:57 PM
Joined: Jan 2011
Posts: 3,487
PV Az @ 5000'
AZjeff Offline
AZjeff  Offline

Joined: Jan 2011
Posts: 3,487
PV Az @ 5000'
By aggressive downshifting if you mean earlier at higher speed that would cause higher revs and would be the opposite of lurching forward. If it were older I'd guess maybe the Idle Air Valve? Not sure what the AFM would have to do with it.


86 Samurai 1.3 leftovers
14 RAV4 2.5 5W-20 PP
16 Silverado 1500 4.3, DI, AFM 5W-30 PP

The most important thing to do in your life is to not interfere with someone else's life. - Frank Zappa

Re: 2012 Silverado lunges forward while braking to a stop [Re: 901Memphis] #4461332
07/16/17 11:14 PM
07/16/17 11:14 PM
Joined: Jan 2007
Posts: 17,501
Clovis, CA
Merkava_4 Offline
Merkava_4  Offline

Joined: Jan 2007
Posts: 17,501
Clovis, CA
Originally Posted By: 901Memphis
Nearly impossible to diagnose across web with the limited info we have


Nonsense! We're all psychic! smile

Re: 2012 Silverado lunges forward while braking to a stop [Re: SquirrelMan] #4461337
07/16/17 11:24 PM
07/16/17 11:24 PM
Joined: Sep 2016
Posts: 183
MN
Tman220 Offline
Tman220  Offline

Joined: Sep 2016
Posts: 183
MN
You're not doing something silly like driving around with tow/haul mode activated are you? (button at the end of the column shifter)

Some people like to drive around all the time with it on because of the firmer and later shifts, but doing so will cause more aggressive engine braking and downshifting while slowing down.


2012 Regal GS Turbo PP 5w30
1994 Camaro Z28 LT1 355 CI, 430 RWHP PP 5W30
Re: 2012 Silverado lunges forward while braking to a stop [Re: SquirrelMan] #4461607
07/17/17 10:28 AM
07/17/17 10:28 AM
Joined: Jul 2017
Posts: 55
In
SquirrelMan Offline OP
SquirrelMan  Offline OP

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In
I am not in tow haul. Definitely high revs. From 2 to 1 is the worst. I have a feeling it's normal. But I read where a guy turned off DOD/AFM and never experienced it again. Stopping gradually it doesn't do it. Only in harder more sudden braking. I maybe wrong in describing lunging or lurching, but it definitely feels like it's under more power than what I am used to. I appreciate the replies, I will check back again. Maybe it's the computer, and it's normal, like an engine braking program? I'm no expert. I service fluids and change filters and gaskets but after that, I am not a knowledgeable mechanic.

Re: 2012 Silverado lunges forward while braking to a stop [Re: SquirrelMan] #4461678
07/17/17 11:34 AM
07/17/17 11:34 AM
Joined: Mar 2016
Posts: 1,945
Western S.C.
CR94 Offline
CR94  Offline

Joined: Mar 2016
Posts: 1,945
Western S.C.
Does this occur mostly when braking on bumpy or uneven road surfaces?


2011 Toyota Prius now at 97K
1981 Mazda GLC (323) retired at 606K
1972 Subaru DL retired at 190K
1954 Chevrolet retired at 121K
Re: 2012 Silverado lunges forward while braking to a stop [Re: SquirrelMan] #4461682
07/17/17 11:39 AM
07/17/17 11:39 AM
Joined: Jun 2010
Posts: 552
stower17 Offline
stower17  Offline

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Posts: 552
I have been in several 2010-2012 Silverados with the 6 speed auto. They ALL clunked from 2-1 downshift and have a "surge" feeling when almost stopped. Even worse with the 4x4 models. I have a buddy with a 2014 that claims the same thing. His words not mine, "the forums say the all clunk and downshift rough". Nature of the best?

Re: 2012 Silverado lunges forward while braking to a stop [Re: SquirrelMan] #4461748
07/17/17 12:32 PM
07/17/17 12:32 PM
Joined: Sep 2016
Posts: 183
MN
Tman220 Offline
Tman220  Offline

Joined: Sep 2016
Posts: 183
MN
Originally Posted By: SquirrelMan
I am not in tow haul.


So what does it do when you are in tow/haul? Get worse, stay the same, etc?

I also believe that transmission has adaptive shifting, perhaps try disconnecting the battery for a bit and letting it relearn? Worth a try, don't you think?

Just noticed you said it was a 4 speed? I didn't think that was still available in 2012 behind a 5.3? If that's really the case then there isn't adaptive shifting but a PCM reset still might do it some good.

Last edited by Tman220; 07/17/17 12:43 PM.

2012 Regal GS Turbo PP 5w30
1994 Camaro Z28 LT1 355 CI, 430 RWHP PP 5W30
Re: 2012 Silverado lunges forward while braking to a stop [Re: SquirrelMan] #4461783
07/17/17 01:03 PM
07/17/17 01:03 PM
Joined: Oct 2014
Posts: 4,285
Utah
CKN Offline
CKN  Offline

Joined: Oct 2014
Posts: 4,285
Utah
Originally Posted By: SquirrelMan
When I brake, it seems to really lunge forward. I can only describe it as aggressive downshifting? I have been advised by a fellow Silverado owner to turn off the Active Fuel Management with Flashpaq? I would love to hear what some of you guys have to say on this. It's a 1/2 ton crew cab 5.3L 4 speed automatic. 2012. Thanks



This is a "feature" of those trucks. It is caused (in part) by the AFM. What I would suggest doing to test this out is to move your selector to the manual position-and then move the gear button to the "5' position. This is great for around town. If the transmission is prevented from going in to 6th-the AFM will not come on.

A tuner is not needed to turn off the AFM. There is a company that makes a black bot that plugs in to the OBD port. You just unplug it when you take it in to the dealer. It DOES NOT OVERWRITE the ECM.

https://rangetechnology.com/

I have the same year as yours in a GMC Sierra with the 5.3. This is my second truck-the first one was a 2011. So I'm pretty familiar with the issues with these trucks.

The issue with a tuner-is that it over writes the ECM (and-yes it can be discovered by the dealer) and will void any powertrain warranty you have.

Last edited by CKN; 07/17/17 01:06 PM.
Re: 2012 Silverado lunges forward while braking to a stop [Re: Tman220] #4462340
07/17/17 10:17 PM
07/17/17 10:17 PM
Joined: Jun 2010
Posts: 552
stower17 Offline
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Posts: 552
[/quote]


Just noticed you said it was a 4 speed? I didn't think that was still available in 2012 behind a 5.3? If that's really the case then there isn't adaptive shifting but a PCM reset still might do it some good. [/quote]

I just noticed he said 4 speed as well... If it's indeed a 4 speed then he has a 4.8 V8 or a 4.3 V6 which neither of those have AFM in those years.

I have driven, rode in, and owned countless 4L60e's for 2 decades and never experienced this 2-1 downshift and surge. So if it's a 4 speed then my experience tells me that something is wrong with that unit.

Re: 2012 Silverado lunges forward while braking to a stop [Re: SquirrelMan] #4462547
07/18/17 07:40 AM
07/18/17 07:40 AM
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SquirrelMan Offline OP
SquirrelMan  Offline OP

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Thanks for your time guys, I have never engaged tow haul. Only had truck since December. I could swear when I bought filter and gasket for tranny I had to specify 4 speed or 6, deep or shallow pan. I also don't remember manual mode showing 6 speeds, I will check. Also, I don't feel the transmission moving through 6 different gears as I build up to 60mph on highway. As a matter of fact, it happens when I pull into McDonald's and it's very rough bump pulling in. I will double check my transmission specs.

Re: 2012 Silverado lunges forward while braking to a stop [Re: SquirrelMan] #4462548
07/18/17 07:43 AM
07/18/17 07:43 AM
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Posts: 55
In
SquirrelMan Offline OP
SquirrelMan  Offline OP

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My cousin actually recommended the Range unit. If I want to turn off AFM. He couldn't stand AFM but he is very particular

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