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#4461226 - 07/16/17 08:53 PM 2012 Silverado lunges forward while braking to a stop
SquirrelMan Offline


Registered: 07/04/17
Posts: 55
Loc: 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

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#4461230 - 07/16/17 08:58 PM Re: 2012 Silverado lunges forward while braking to a stop [Re: SquirrelMan]
901Memphis Offline


Registered: 08/14/10
Posts: 12893
Loc: Northern Kentucky
Nearly impossible to diagnose across web with the limited info we have
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#4461244 - 07/16/17 09:22 PM Re: 2012 Silverado lunges forward while braking to a stop [Re: SquirrelMan]
SquirrelMan Offline


Registered: 07/04/17
Posts: 55
Loc: In
Other forum discussions I have found describe it as "lurching" forward. Happens as transmission downshifts.

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#4461246 - 07/16/17 09:23 PM Re: 2012 Silverado lunges forward while braking to a stop [Re: SquirrelMan]
mrgrim Offline


Registered: 08/04/13
Posts: 62
Loc: 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.

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#4461276 - 07/16/17 09:57 PM Re: 2012 Silverado lunges forward while braking to a stop [Re: SquirrelMan]
AZjeff Offline


Registered: 01/14/11
Posts: 2630
Loc: PV Az
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.
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#4461332 - 07/16/17 11:14 PM Re: 2012 Silverado lunges forward while braking to a stop [Re: 901Memphis]
Merkava_4 Offline


Registered: 01/30/07
Posts: 17501
Loc: Clovis, CA
Originally Posted By: 901Memphis
Nearly impossible to diagnose across web with the limited info we have


Nonsense! We're all psychic! smile

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#4461337 - 07/16/17 11:24 PM Re: 2012 Silverado lunges forward while braking to a stop [Re: SquirrelMan]
Tman220 Offline


Registered: 09/20/16
Posts: 144
Loc: 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.
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#4461607 - 07/17/17 10:28 AM Re: 2012 Silverado lunges forward while braking to a stop [Re: SquirrelMan]
SquirrelMan Offline


Registered: 07/04/17
Posts: 55
Loc: 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.

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#4461678 - 07/17/17 11:34 AM Re: 2012 Silverado lunges forward while braking to a stop [Re: SquirrelMan]
CR94 Offline


Registered: 03/20/16
Posts: 1120
Loc: Western S.C. since 1996
Does this occur mostly when braking on bumpy or uneven road surfaces?
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#4461682 - 07/17/17 11:39 AM Re: 2012 Silverado lunges forward while braking to a stop [Re: SquirrelMan]
stower17 Offline


Registered: 06/15/10
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?

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#4461748 - 07/17/17 12:32 PM Re: 2012 Silverado lunges forward while braking to a stop [Re: SquirrelMan]
Tman220 Offline


Registered: 09/20/16
Posts: 144
Loc: 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.


Edited by Tman220 (07/17/17 12:43 PM)
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#4461783 - 07/17/17 01:03 PM Re: 2012 Silverado lunges forward while braking to a stop [Re: SquirrelMan]
CKN Offline


Registered: 10/14/14
Posts: 3686
Loc: 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.


Edited by CKN (07/17/17 01:06 PM)

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#4462340 - 07/17/17 10:17 PM Re: 2012 Silverado lunges forward while braking to a stop [Re: Tman220]
stower17 Offline


Registered: 06/15/10
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.

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


Registered: 07/04/17
Posts: 55
Loc: In
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.

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


Registered: 07/04/17
Posts: 55
Loc: In
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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