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Chevy Silverado and GMC Sierra Active Fuel Management Problems



  • Thanks for all your, really knowlegable, advice.

    I'm glad you got one of the trucks with the AFM working correctly and gets good gas mileage. Consider yourself lucky!

    Take Care
  • Some 2011 Silverado 5.3 engine owners don't know it, but you can see if your Active Fuel Management is working while you are driving. It's on your Instant Fuel economy gauge. You will see it switch back and forth from V8 to V4. It will always go into V4 when the road grade is declining or you are slowing to stop. You aren't using much gas then anyway. It is supposed to be in V4 when cruising at a normal steady highway speed (unless you put it under more load like going uphill). The explaination is on page 9-40 of your owners manual.
    Apparently, some owners don't realize that their poor gas mileage, at normal highway speed (around 70 MPH) is because the AFM system is not working as advertised by GM and their sales people. If you are not getting the gas mileage you expected, that's probably the reason. The hidden surprise is, THERE IS NO FIX, according to the GM engineer who looked at my problem. When you test drive one of these, be sure and check to see if it's working properly. Apparently some do, and some do not. And most of the sales people don't really understand how and when it works. They will tell you anything to get you to buy it. BE CAREFUL and verify what you are told. Talk to the mechanics, if you can.
  • donl1donl1 Posts: 109
    I have a 2009 Crew Cab LTZ 4X4 with the 5.3 and AFM. You can use the DIC to watch it go from 8 to 4 cylinders and I can guarantee it doesn't spend much time in the 4 cylinder mode. That being said I'm satisfied with the overall mileage. In the summer it's usually in the 18 mpg area. The best ever was an even 21 driving 65-70 on flat ground with no AC. A two and a half ton vehicle with the aerodynamics of a refrigerator is never going to be a mileage queen...I don't care whose logo is on the tailgate. I see the 4 cylinder mode going down hill or feathering the throttle on the level around the 60 mph range. If it only needed a 4 cylinder motor for everyday driving that's what they would have put in it. But in the real world it needs a real motor.
  • chuck1chuck1 Posts: 1,405
    edited November 2011
    I run very short trips in mine-mostly 2 1/2 miles. I get between 13 and 14. On a 80 miles round trip the other night I got 17.5mpg. The mpg is right where I would expect it. The 22 0r 23mpg some people SAY they are getting is a fairy tale.

    You don't buy these for mpg. You buy them for utility. If you don't need the utility, stick with a crossover or sedan, there are many excellent choices in both types.

    I tow a travel trailer with mine-that's why I bought the truck.

    Once you drive over 70mph-you are NOT GOING to see the 4cylinder mode come on.

    I think some on this board were "SOLD" the truck rather than buying it by choice and regret the less than stellar gas mpg once the "ownership experience" set in. Now, they are putting the blame on GM instead of squarely on themselves.
  • Their sales pitch is that they do serve the purpose of two motors. The "real motor", eight cylinders when you want or need it, and four cylinders when cruising on level highway. If the 4 cylinder mode of the engine was never to be useful for this truck, why go to the trouble of building it? Besides, if you don't need or want 4 cylinders, why spend the extra money to buy it?
  • chuck1chuck1 Posts: 1,405
    Obviously, you had some major twisting or misrepresentation of what the truck is designed to do. You were sold something you shouldn't have purchased. It's not GM's fault.
  • The dealers and their sales people DO represent General Motors!

    If you bought a computer from an HP dealer and it was represented to have 7 GHz. When you fired it up and saw it only had 5 GHz. Don't you think HP or their representatives should make it right. Or, should you just say, it's all my fault, I shouldn't have bought it anyway, that's way too much capacity for me. OH, and by the way, I want you to keep the extra money you charged me for it! I should have known better. Thanks for the time you took to sell it to me.
  • chuck1chuck1 Posts: 1,405
    First of all, the dealers that sell GM cars are independent businessmen. I really don't think it's realistic to expect GM to be accountable for everything a sales person says in the sales process. If you would have come on this board before your purchase, I would have been the first one to tell you about the REAL WORLD fuel consumption. ALL OF US on this board would have helped you.

    As it stands you have one of the worst case of buyer's remorse/regret I have seen.

    GM is not going to write a separate software program (even if it's possible) just for you because you bought too much vehicle for your needs.

    Move on...I know I am.
  • Thanks for all your GM biased advice.

    I see you have posted here over 1500 times.

    I am moving on....I'm glad to see you will be too.
  • chuck1chuck1 Posts: 1,405
    I see you have posted here over 1500 times.

    Been a member many, many years.
  • String2,

    I am asking our Technical Assistance Center about your question pertaining to the 6% throttle/pedal setting and how it relates to the activation of the AFM system. Thank you for your patience – I will post the information as soon as I have heard back from them.

    GM Customer Service
  • Thanks Sarah,
    Can you find out if there is a tech. bulletin about the 6% throttle corrections or adjustments? I don't think most of the dealers will know. This may or may not be my problem. If they have read my truck symptoms, as them if they have any other ideas that may work.
    Thanks again.
  • Hello again string2,

    Here is the information that our center responded with:

    “There are multiple Parameters that must be met for the cylinder deactivation to become active. One of the parameters is the throttle angle of 6% or less. Even if the throttle angle is less then 6% the cylinder deactivation will not become active if the other parameters are not met.”

    In regards to any further diagnostics, the center did rely upon the engineer who has looked into your vehicle per one of the Service Requests open with us and did not make any further recommendations.

    Where tech bulletins are concerned, there are none posted in our database at this time.

    I hope this is helpful for you,
    GM Customer Service
  • chuck1chuck1 Posts: 1,405
    edited November 2011
    Going 75mph is probably not within those parameters. Nor, should it be expected. Even a vehicle that is expected to get good mpg will get less at high speed. I see nothing wrong with the technical information relayed back to you.

    Somehow I think others will not be happy with this information.
  • string2string2 Posts: 71
    edited November 2011
    Hi Sarah,
    Thanks for your response, Can you ask your GM Tech. if the AFM is designed to work at 70+ MPH on level highway, not hauling anything or pulling a trailer. Some owners say their AFM works above 70 MPH. Others argue confidently that the AFM is only designed to work below 60 MPH, on level highway.

    According to GM's "Cylinder Deactivation System Description" Document ID: 1995547, two of the parameters are, the vehicle speed must be more than 15.5 mph and the engine speed is between 700 and 2800 rpm. On my truck, 70 MPH is about 1900 RPM. My AFM stops working on level highway between 55 -60 MPH. I sure would like to get a definitive answer before I take my truck back in for service next week.
  • 08max08max Posts: 1
    Chuck, actually, at 75 my silverado max gets the best gas mileage( except at around 45) and the afm works at even higher speeds.
  • chuck1chuck1 Posts: 1,405
    According to the above, in theory the AFM will come on at 75mph. It's never happened to me. But then again, the highway would have to be perfectly flat, with no winds whatsoever.

    I have never driven in those "ideal" conditions".

    Even on my 20 mpg trip, the AFM wasn't on all the time.
  • chuck1chuck1 Posts: 1,405
    Your truck in an anomaly according to all the other owners (Silverado/Sierra) who communicate their mpg on the various truck forums on the Internet.
    Congrats for such great mpg.
  • I have a 2008 gmc sierra last 8 vin 8Z160870 4WD pickup was running when parked would not start in morning did some test was not getting fuel assumed fuel pump 115,000 miles,replaced fuel pump and still would not start. applied power to pump and pickup started removed power and truck died. have no power at 20amp pump fuse, key on or off, pump relay has power but jumping relay dosent work any ideas
  • I ran your VIN in our system and did not see any open recalls on your vehicle. Because of the high mileage, you are outside of the parameters of the vehicle's warranties. For the future, it may be best to share this information privately through email as this does specifically identify your vehicle.

    Was the fuel pump replacement done at a GM dealership? If so, we can follow up on that. Please email us more information, including your name/username, involved dealership, and contact information.

    GM Customer Service
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