July 8, 2016 at 6:27 am #132832
New member, first post. I am considering buying a new Silverado 1500 with the 6.2L 8-speed, but I am concerned about the AFM (cylinder deactivation) effect on compression braking. I live in the mountains of Colorado and regularly down shift when going down some long grade to control the truck’s speed instead of riding the brakes. It appears that going down hill qualifies as a “light load” condition so I would only get the benefit of four cylinder 3.1L compression braking instead of 6.2L compression braking. I do not want to permanently turn off the AFM because I do want the added fuel mileage. Any ideas on how to momentarily turn off the AFM? I sure don’t want to be replacing the brake pads every 20k miles.
July 9, 2016 at 1:41 pm #132892
Hello @coloretiree and welcome to GM Authority!
I also live in Colorado and have drove the 2014 Silverado when it came out as a company vehicle. Though I didn’t do much towing with it, I did use it to go on many a ski trip in the mountains through I-70. The truck had the 5.3L and 6-speed transmission, but the 6.2L behaves similarly, albeit with more power.
Now, more pertinent to your question: the way I have always understood it, AFM doesn’t actually stop the valvetrain of the deactivated cylinders, but rather stops “feeding” them, thereby attaining the fuel savings. There is a lot of misleading literature out there saying that the inactive four cylinders are “shut off”, but I believe that’s an over-generalization. So, I don’t think AFM will impact engine braking for you. Does that help at all?
July 12, 2016 at 2:45 pm #133068
Thank you for taking the time to help me out. Since I posted my question, I found on the net a description of exactly how AFM works. The article explained how, in addition to cutting off fuel to the non-active cylinders, both the Intake and Exhaust valves on cylinders 1, 7, 4, and 6 were actually held in a closed position while the AFM was active. By doing that, the non-active cylinders acted like pneumatic springs so there was no net pumping loss from the non-active cylinders and, unfortunately for me, no contribution to compression braking .
On the brighter side, other sources of wisdom stated that AFM was disabled when the transmission shift lever was moved to the Manual (M) position, which is of course how a person would downshift to enable compression braking, so maybe all is not lost after all.
And as we all know, if its written on the internet, it has to be true. 🙂
Thanks again for your help and have a great COLORADO day!
July 14, 2016 at 8:15 pm #133281
Yup, that’s exactly how AFM works.
And I should have thought of the solution to shifting to manual mode . That does, indeed, disable AFM.
Cheers and have a great Colorado day as well 🙂
August 2, 2016 at 6:52 am #134912
My 2015 Sierra Denali has grade braking. When it senses I am using the brakes the transmission automatically selects a lower gear etc. So look in grade braking, it should be a standard feature on the Silverado.
Re: Transmission, 6-speed automatic, electronically controlled with overdrive and tow/haul mode. Includes Cruise Grade Braking and Powertrain Grade Braking.
Requires Double Cab model and (L83) 5.3L EcoTec3 V8 engine. Requires Crew cab model without (NHT) Max Trailering Package or (L86) 6.2L EcoTec3 V8 engine.
Requires Double Cab model and (L83) 5.3L EcoTec3 V8 engine.
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