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Chevy Silverado and GMC Sierra Active Fuel Management Problems



  • string2string2 Posts: 71
    If you haven't looked at your instant fuel economy guage when AFM kicks into v4, the miles per gal. jumps 6 to 10 mpg. The problem is getting it to kick in at normal hwy driving speed. By the way, if the AFM doesn't kick in at hwy driving speed, it is not designed to trip a trouble code unless there is something else also wrong with it. Because there is no trouble code is the reason the mechanics keep telling us that "it is working normal". They only know to fix what the computer shows them is wrong.
  • GM_BlaineGM_Blaine Posts: 3
    I have had precisely the same problem. But it's not lifter, it sticking piston rings. I had all pistong, connecting rods and rings replaced under warranty and now the oil consumption has stopped. It's interesting that my problem started at precisely the same mileage as yours. And like you I only drive highway miles about 45 every day to work by myself. I am taking legal action as I still owe money on this vehicle and I think the problem will return after about 30,000 miles. Our other GM vehicle operates flawlessly! We have to drive the older unwarranteed vehicle on road trips because the newer warranteed vehicle with far fewer miles is not reliable.
  • GM_BlaineGM_Blaine Posts: 3
    I am in the same boat. I too bought a $42,000 vehicle that needed the pistons and rings replaced after 60,000 miles.
    I drive the truck like an old lady. But the engine started burning oil like nobody's business after the first 50,000 miles. I have not been able to use it properly for the past 12 months as it has been back and forth to the dealer
  • sh_tchevysh_tchevy Posts: 1
    There is a corporate bulletin available to dealers only regarding the oil consumption in the 5.3 flex fuel engine with multi-step recommendations on how to address the issue...the final fix is new piston and rings. We have had ours in the shop 3 times now...I believe GM is prolonging as long as possible for vehicles to go past warranty to avoid the huge costs of repairs. The bulletin covers multiple years and multiple models. We were told we were "not supposed to have is for dealers only." Once GM realized we had the bulletin they covered our vehicle under "good will" with a new valve cover and oil pump but refused to replace the piston and rings....I see class action looming. After being completely loyal to GM for over 20+ years we will not be repeat customers ever.
  • chuck1chuck1 Posts: 1,405
    Have you ever been involved in a class action? The most you can expect is a $500.00 coupon towards a new car or truck from GM. The least you can expect is a free oil change. Class actions settlement usually involved the Lawyers getting millions. The consumers getting very little.
  • string2string2 Posts: 71
    Well after a year of trying to get a straight answer & 10,000 miles on my 5.3 2011 Silverado crew cab truck. I finally complained to EPA and they were instrumental in having GM take a special look at my truck. My problem is poor gas mileage and AFM not working on flat highway above about 63 MPH. The following is their explanation after their analysis.

    I was allowed to speak to one of their engineers who was a specialist concerning this problem. He said he could see that there was a drag on the motor. He questioned the computer program designer to see if an engine Calibration change would help with this problem. What he explained to me was this: If the engine is calibrated to operate in V4 at the normal highway speed limit of 70 MPH, the catalytic converter would not stay hot enough to maintain the correct exhaust emissions to satisfy EPA. Question: How are they allowed to get away with advertising their AFM as a fuel saving feature if it is not designed to work on flat highway with cruise control on and driving the normal 70 MPH speed limit. If they all have the same drag on the engine and all work just like mine, then it seems like the average EPA sticker on the window should read 15 City and 16 Highway / AC on (about the same in cold weather).
  • chuck1chuck1 Posts: 1,405
    edited June 2012
    "If the engine is calibrated to operate in V4 at the normal highway speed limit of 70 MPH, the catalytic converter would not stay hot enough to maintain the correct exhaust emissions to satisfy"

    Seems still to be some conflicting information. After numerous 600 mile road trips, my AFM works at 70mph and nets me 20mpg on the highway. HOWEVER, it will not work ABOVE 70mph.

    I have not had any check engine lights or anything to come on to suggest this isn't normal.

    Apparently, good or bad, not all trucks operate like yours.

    I have taken numerous (5 to 6) trips from So. Cal to Salt Lake City, UT. documenting this fact.
  • string2string2 Posts: 71
    Seems still to be some conflicting information. After numerous 600 mile road trips, my AFM works at 70mph and nets me 20mpg on the highway. HOWEVER, it will not work ABOVE 70mph.

    I have not had any check engine lights or anything to come on to suggest this isn't normal.

    Apparently, good or bad, not all trucks operate like yours.
    Hi Chuck,
    Without a doubt, i'm stuck with a bad truck or engine. I'll be trying to sell it soon. It's a shame because it's a nice looking truck and handles well. Chuck, the GM engineer said they checked the computer programming on several trucks like mine, and they were all identical to mine. I told the engineer that this website and others have posts from Silverado owners stating they get 20+ miles per gallon. He disputed that and said if my truck did go into v4 under the conditions I've stated, it wouldn't be operating as designed, the catalytic converter would cool down and be out of compliance with EPA emission guidelines. This information came from the engineer in charge of designing the calibration for all the GM light duty trucks. By the way Chuck, this problem does not trip a trouble code. Otherwise, it would be tripping all the time. The computer will stay in V8 if you are going uphill or pulling an extra load or driving into a strong headwind. It's not designed to trip a code because of extra load on the engine. Mine probably has a minor problem somewhere that is creating just enough drag to keep the V4 from working under those conditions and they don't know where to look for it.
  • chuck1chuck1 Posts: 1,405
    It's too bad your not happy with your truck. If your financially able to do so, unloading it is the right thing to do. I would hate to get behind the wheel of a car/truck that I am not happy with.

    The Silverado's new 6 speed transmission isn't the greatest. I bought my Chevrolet for literally thousands less than a Ford, and even bigger difference on the Tundra. I considered a Tundra because I had a 4Runner that was basically flawless for 80,000 miles. The weird frame under the bed of the Tundra scared me away. If you do a google search, you will see numerous transmission complaints with the new Ford F150 as well.

    Good luck to you.
  • Ok my PS 2008 silverado nothing but problems now at 78000 using 3 quarts every 5000 miles.How did you get your problem resolved thanks
  • 3jp3jp Posts: 3
    My wife drives the 08 sierra 4x4 crew cab 6.0 and the engine light came on and the oil pressure guage quit. She pulled into an autozone and had the guy check to see if it had oil. The dip stick did not show any and 1 qt was added, still no oil on dip stick. added a 2nd qt and still no oil. a total of 4 qts were added. Next day she took it to where she gets the oil changes and it was over by a qt and a half. the computer said she still had 30% life left on the oil. Why does a truck this new with 85k miles on it use this much oil? there are no leaks. Time to go see the dealer to see if we have a problem.
  • Good morning 3jp,

    Please keep us updated on the progress of your investigation with the dealership; if you want for us to check into it further we can set up a Service Request and do so. Please email us at with more details (including your name and Edmunds username, phone and address, the last 8 digits of your VIN and current mileage, and the name of your dealership).

    Sarah, GM Customer Service
  • string2string2 Posts: 71
    Check to make sure the drain passage from the heads back to the oil pan is not being restricted in some way, but it may still be using a little oil.
  • chuck1chuck1 Posts: 1,405
    So basically the truck needed two quarts of oil. How many miles were on the oil since the last oil change?

    GM considers a quart every 1,000 miles as normal. If the truck had 2,000 or so miles on it since your last oil change it would be considered "normal".

    You need to check the oil every other fuel stop. And coach your wife not to stop at an Autozone where apparently they don't know how to add a proper amount of oil.
  • rem308rem308 Posts: 3
    My 2008 1500 pickup started running very very rough all of a sudden. I went to the closest mechanic I could find in a very small town. We don't have a GM dealer. He told me GM is having all kinds of problems with the 2007 and 2008 1500 5.3 engines. Fuel mileage and oil consumption is the smallest of the problem.
    Luckily, he owned a Device that read codes he got from Napa. It showed the number 6 cylinder was bad and an O2 sensor.
    He put in all new plugs, new plug wires and one O2 sensor. He took it for a test drive and within two miles it was it was doing the same thing. The Stablizer and traction control light came on and also the check engine light as it had for me when it started running very very rough. In my case, it was the number 6 plug. Three different GM mechanics at three different dealerships told me that it mostly affects the plugs on the right bank, and can affect any of those plugs, one told me that he had seen it on the number 7 plug twice.
    GM is well aware, as well as their service depts since GM has issued bulletins to the dealers regarding this issue. These bulletins are not for the public.
    What happens is the fuel mgt system shuts off the fuel to the right bank and the lifters won't lift the valves for lubrication. Then, the lifter fails, the roller for example breaks off, the lifter slides inside itself, etc. as a consequence it wears the lobe off the camshaft, then destroys the camshaft. Replacing the bad lifter and camshaft will not solve the problem, maybe temporially, but not for the long term.
    In my case, my pickup went out of warranty, GM refused to fix the problem. If you are having any issue with oil consumption, bad fuel mileage, running rough; RUN DON'T WALK TO YOUR NEAREST GM DEALER ESPECIALLY IF YOU ARE UNDER THE 100,000 MILES AND DEMAND A NEW ENGINE.
    Repairing the engine does not work. I was told by one mechanic he saw an engine repaired with a new lifter, etc. and a few thousand miles later, he had the same problem and ended up buying a new engine.
    The only thing to do is get a new engine. Guess what? GM now has their fuel mgt. system on the 2013 2500's and as I understand it on the 3500's also.
    It looks like I'll be buying a ford sooner than later. We can thank California and the EPA for all this crap the manufacturers have to put on vehicles these days.
    However, it really pisses me off with service managers and a district manager lies to me about the problem.
  • chuck1chuck1 Posts: 1,405
    "He put in all new plugs, new plug wires and one O2 sensor. He took it for a test drive and within two miles it was it was doing the same thing. The Stablizer and traction control light came on and also the check engine light as it had for me when it started running very very rough. In my case, it was the number 6 plug. Three different GM mechanics at three different dealerships told me that it mostly affects the plugs on the right bank, and can affect any of those plugs, one told me that he had seen it on the number 7 plug twice."

    S0-he did work that really wasn't going to cure the problem and misdiagnosed what the issue(s) were?

    How many miles exactly did you have on the truck?

    Your truck is out of warranty.

    How long do you think any manufacturer should be responsible for your vehicle?
  • rem308rem308 Posts: 3
    100,000 miles, it now has 105,000.

    The problem definitely was occuring prior to 100,000.

    Apparently, you are a GM employee, your tone certainly indicates it.
  • chuck1chuck1 Posts: 1,405
    edited October 2012
    Not a GM employee - not at all. But there are several posts like yours. Who's fault is it that YOUR MECHANIC did not diagnosed the problem correctly?

    How long should manufacturers be liable for mechanical issues? 100K? 200K? 300K?

    It's easy to get on the Internet to complain. Harder to get some real facts on this forum sometimes as to what the real circumstances are.
  • string2string2 Posts: 71
    Apparently, you (Chuck 1) are a GM employee, your tone certainly indicates it.
    Hey rem308
    It's obvious that Chuck1 is being paid well by GM. It looks like he's been posting on this site for years and always very quickly degrades anyone's compaint and sides with GM. NOBODY would waste that much time making himself available to respond in the defence of any giant corporation without being paid unless.........., well I can't think of any other reason??
  • chuck1chuck1 Posts: 1,405
    edited October 2012
    I have been posting for years because I have been a member of Edmunds for that long. In addition, if you check my posts it is clear what cars I have owned. As an ex-owner of a Toyota 4Runner (that I towed with) and Honda Accord, I have contributed on those forums. Check out the 4Runner towing forum. A GM employee would NEVER OWN A TOYOTA!


    The thing that gets me agitated is when someone comes on here and says my truck isn't working right because the alternator is discharging. IT'S SUPPOSED TO WORK THIS WAY!

    This isn't fair to people who are looking at these vehicles.

    Then they try to justify what they are saying because they work on computers.

    OK-I guess some know more than the engineers who designed the Silverados.
  • rem308,
    I agree with you 100% How do we get the word out about these AFM engines? I share your pain too. I didn't realize these were defectively engineered engines until now.

    I have a 2008 4x4 Z71 with 5.3L AFM. Primarily highway driven miles with weekend hunting trips, but no heavy duty offroading. Oil changes at recommeded intervals; minimal oil loss between.

    At 145,000 miles, the lifters & camshaft went out. I think AFM shortens engine life. I've owned GM trucks(and Fords and Dodges) for three decades & normally get 300K miles from a motor. Of course, GM won't even share in the cost of repair - which is several thousand dollars - as the mileage is out of warranty. Even though I like the styling, handling & performance in muddy conditions, I'll be swapping for a Ford or Dodge or try a Toyota asap.

    Like you, if you own one of these engines, be sure to trade if off before the warranty expires, or even better, buy something else to begin with!
  • chuck1chuck1 Posts: 1,405
    How long do you think a manufacturer should be responsible?

  • chuck1,
    You have a valid question. My answer is "it depends". I purchased my first chevy truck from this dealer in 1985 and several more since then. Have not had internal engine trouble in the past. Have rigorously followed maintenance schedule for safety reasons and to avoid costly repairs such as this. Have paid premium cost at the dealer for such service and expected more from them. Our government also used some of my tax dollars to bail out General Motors during the fiscal crisis. I personally purchased the 2008 Silverado, also helping out GM in their time of need. I could have bought a Dodge, Ford or Toyota. I've had excellent experiences with all three brands.
    AFM technology was first used in the 2007 truck. I wasn't aware of premature lifter failure until my truck broke. This was a surprise and not a good one. There is a design flaw in this system. Lifters need lubrication to perform properly over the long term. There should at least be a disclaimer that lifters and camshaft will need replacement after the initial warranty so that as consumers, we can include these costs in our buying decisions. After all, purchasing and maintaining a vehicle for most people is our largest investment after our home.
    I wanted GM to at least cover the cost of the parts and for the dealer to discount the labor. Denied by both.
    I hope these forums inform others in their purchasing decisions, both for used vehicles equipped with AFM engines and for buyers of new vehicles that intend on keeping them past warranty.
    Now, back to your original question. Warranty of 100,000 miles is excellent. Most folks don't drive the high highway miles that I do so probably will never reach that level. For individuals like me that drive a lot, allow the dealer to perform all service work and properly maintain their vehicle, mileage should be extended on engines possibly for lifetime of ownership. They should at least cover longer timeframe for new, untested technology.
  • raldoraldo Posts: 1
    We have a problem with our AFM, when we're in V8 mode, the motor has a squealing sound. At first I thought it was the idler pulley or the tensioner...but I removed all the belts and started the truck. The squeal was still there, I thought it was the seal on the crankshaft but when I crawled under the truck, the sound got louder and more toward the rear of the truck, like near the transmission. We took the truck for a drive and we noticed the when the truck went into V4 mode, the squeal went away. When it went back into V8, the squeal came back. Anyone else have this problem? :sick:
  • gmcustsvcgmcustsvc Posts: 4,251
    If you were planning on working with a GM dealership to get this checked into, we're available to check in on this with them. Please contact us via email at with more information (including your name and contact information, a brief summary of the situation, the last 8 of your VIN and mileage, and the name of your dealership).
    Sarah, GM Customer Service
  • I wish I had done a little more research before I purchased this 2008 GMC Sierra. It doesn't have the display that shows when active fuel management is working, so I didn't think it had it. Unfortunately after doing a little research, I found out that it indeed does have it since it is a 5.3. It is also flex fuel compatable (E85). I have only had the truck for less than a month. I purchased it Certified Used from Serra of Jackson, TN with 50k miles and one owner before me. I noticed no problems on the test drive, or the drive home into Mississippi. When I got home, I noticed a slight tick that sounds like lifter tick. I wasn't overly concerned with that. When the weather got cold for the first time, the tick was much more pronounced when the vehicle was first started, but it would go away in literally seconds.

    I knew I had real trouble when I put 87 octane in it. The truck started to spark knock pretty bad at light throttle. Assuming I might have gotten bad gas (bought it at Shell), I put some Heet in the tank. This did nothing. I ran that tank of gas and put two bottles of Techron in at next fill up, and I filled up with 89 octane (Pilot). Slight improvement. The next tank was 87 Pilot octane with 2 bottles of Techron. The truck will spark knock like mad at light throttle at about 45 mph. It seems to me that it's spark knocking the entire time it's in V4 mode. Salesman at Serra told me to "put some Techron in it". I told him I already did and that it didn't help, but no check engine light had come on and would I be wasting my time taking it in for service. He said he'd ask and call me back. I never heard from him again. I took it to a local dealer and complained and left it with them. The tech that drove it heard nothing, and the service manager said that some AFM noise was normal. I tried to believe him because I like the truck, but the spark knock is annoying and is most likely damaging the engine. So, I return to the dealership and drive it with the same tech inside. I keep him in there until it spark knocks like hell and ask if he hears that. He says he didn't hear anything other than exhaust noise. Whatever, everyone else that rides with me in the truck can hear it, and no exhaust noise sounds like spark knock. If it was exhaust noise, it would be more rythmic than it is. Finally, to prove it was spark knock, I filled up with 93 octane. Spark knock almost completely gone. If it was exhaust noise, it would remain the same. I went to the dealership and asked about trading it in on a new 2012 model, and they had one left. I test drove it, and it sounded nearly as bad as mine. I'm certain it is spark knock, and I'm certain the reason it is happening is because the timing is a little off due to weak opening / closing AFM valves during V4. The dealership was nice enough, and sort of eventually admitted to hearing something, but said half of the vehicles with AFM do it and it wasn't worth tearing down the engine and replacing valves, because GM wouldn't pay for it anyway if the offending valves and lifters weren't too far out of spec.

    So after a little research and thought, I'm convinced it is indeed spark knock, being cause by bad valves or lifters (which there is a TSB about). I'm also convinced the dealerships have to say they don't hear it or it isn't a problem because GM isn't going to reimburse them for any work unless it's really bad. GM, in order to save money, doesn't believe in repairing something to prevent catastrophic disaster, only repairing the disaster after it happens. So I've got $24k or so in a "certified" (yeah, right) used vehicle that I hate to drive now. I suppose I can put some more 93 octane in it and run it for a while. That'll eat up whatever cost savings I might've gotten with AFM. I considered having the AFM shut off. But, what I'm most inclined to do is fill it with 93 octane and trade it in on a Ford. I know all vehicles have their problems, but I had a 98 Dodge that I loved and always heard the rumors of weak transmissions. I babied that truck and changed trans fluid every 50k miles, only to have it fail twice at 130k and 170k. I sold it with 190k because it still didn't shift gears right. I don't want to try and put Mobil 1 every 3k miles in this truck and run 93 octane to try to avoid the innevitable AFM valve failure. I guess if there's enough rumors of problems with a particular vehicle, they're probably true to some extent. And the AFM rumors are pretty rampant. I know all AFM engines aren't bad, but why would I want to gamble on another?

    Sorry for the rant. Not 100 percent sure what my best course of action is to be honest. To sum up, 53k miles now, and I've had it for a month. 10k miles or 11 months on the warranty. It spark knocks like hell on 87 octane, especially in V4 (shouldn't do that if it'll supposedly run on E85), and GM dealer says they can't hear anything abnormal. No CEL....yet. Any advice appreciated. Or I will sell it to you at a great discount if you live in the area.
  • chuck1chuck1 Posts: 1,405
    You have a 100K power train warranty. Drive until it blows up and you should get a new motor. Document all your visits to the dealer.
  • gmcustsvcgmcustsvc Posts: 4,251

    One thing we can do is document that you're having this concern and follow up with your dealership on this for you. Please email us at with more information (including your name and contact information, the last 8 digits of your VIN and mileage, the name of your dealership, and a brief summary of the situation).

    GM Customer Service
  • It's a 2008. The powertrain warranty is up 5 years after it's initially sold. Which is now. I have 11 months on the remaining "certified used" warranty. Factory warranty is expired. Have been documenting visits to dealer, though, thanks.
  • jswain2jswain2 Posts: 16
    edited December 2012
    Will do, thanks. I called the dealership where I initially bought the vehicle again yesterday. The salesman was nice enough. He got the service manager to call me back today. The service manager seems to think it may be being caused by carbon build up, which is feasible. I'm going to try some carbon cleaner on the engine as he recommended and go from there. I'm hopeful, but a little doubtful that will resolve it, since the engine only has 52 or 53k miles. I have already used 4 bottles of Chevron Techron in the gas....I assume it would clean carbon deposits, but am unsure. Going to try something a little more aggressive and see what happens. If it doesn't work, I'll either get the dealership to fix it under warranty or trade even for a like vehicle at that dealership. Otherwise, I'll put some 93 octane in it and trade it for a Ford or Toyota. Not saying they're better vehicles, I'm just not real wild about the AFM and I don't think they have it.
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