Chevy Silverado and GMC Sierra Active Fuel Management Problems

string2 · November 2011

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

string2 · November 2011

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.

donl1 · November 2011

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.

chuck1 · 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.

string2 · November 2011

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?

chuck1 · November 2011

String,
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.

string2 · November 2011

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.

chuck1 · November 2011

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.

string2 · November 2011

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.

chuck1 · November 2011

I see you have posted here over 1500 times.

Been a member many, many years.

gmcustsvcsarah · November 2011

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.

Best,
Sarah
GM Customer Service

string2 · November 2011

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.

gmcustsvcsarah · November 2011

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,
Sarah
GM Customer Service

chuck1 · 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.

string2 · 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.

08max · December 2011

Chuck, actually, at 75 my silverado max gets the best gas mileage( except at around 45) and the afm works at even higher speeds.

chuck1 · December 2011

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.

chuck1 · December 2011

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.

cologuy · December 2011

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

gmcustsvcsarah · December 2011

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.

Regards,
Sarah
GM Customer Service

string2 · December 2011

I now have about 5,000 mi. on my Silverado. Just filled up AGAIN with 21.2 gallons of gasoline. My gauge showed 321 miles since last fill up. My Active fuel management won't work above 60-65 MPH, therefore, I don't get the benefit from the Active Fuel Management at normal highway driving around 70 mph. GM has looked at it and assures me that it's operating normal dispite their misleading epa window sticker 15 city 21 highway.
I get about 15 city 16 on level highway above 65 MPH. Not loaded and I don't have a heavy foot. gas - Shell, Exxon, Chevron

321 miles divided by 21.2 gallons gas = 15.14 MPG city miles 50% highway 50%

Since the Active fuel Management is not designed to work above 65 MPH on level highway, I can't get the fuel savings at the highway speed of 70 -72 MPH. I don't know why they designed it that way, but GM says that's normal. Are they lying to me ?

chuck1 · December 2011

Those who have had a custom tune and the AFM disconnected report a 1 mile-per-gallon difference on the highway. Those guys are reporting 19ish on the highway.

It would appear that there is more at play than the AFM not working. It would not contribute to only 16mpg highway if it WASN'T WORKING.

Your mpg will suffer greatly at speeds above 70mph.

string2 · December 2011

It would appear that there is more at play than the AFM not working. It would not contribute to only 16mpg highway if it WASN'T WORKING.
Your mpg will suffer greatly at speeds above 70mph.
====================================================

No kidding!! I think you're right! It would appear that there is more at play here than the AFM not working. But there's no trouble code.

The fact is, it suffers greatly above 63 MPH, or less. A GM engineer checked it out and said it was working normally, even though he couldn't get the AFM to work hardly at all above that speed. At 67 MPH it doesn't work at all unless going downhill. It has stayed the same since I bought it and has no trouble code!
I can tell you what's wrong, though. It's hitting on all 8 cylinders, all the time, when the AFM isn't working. And that's pretty much all the time over 60 MPH. If you know the answer to this, will you please call GM and let them know.

castonguayh · December 2011

:mad: The AFM is a problem across the board. Just got a camaro with it and will be trading it in in the spring. I had not bought a GM car since the 80's because of transmission problems but thought I would give them another try.

I will not buy another GM machine - ever - and will tell everyone I know and enter on every forum I can find.
:mad:

chuck1919 · December 2011

If the Cameros are having problems it's a big secret, just did a google search and couldn't find much.

The Camero is outselling the Ford mustang, it's not even close.

lstrip · January 2012

if you do a little research on these forums, you will see that chuck1 and chuck1919 are the same person. also you will soon realize that he
instantly responds to any negative post reference our gm vehicles. and he is on every forum.
chucks has posted and quoted numerous documents that are not available to the average customer.
when reading a reply from chuck1919 or chuck1 just remember that he is here only to refute any negative post.
that's what he gets paid for. (by gm)

chuck1 · January 2012

Yes, both Chucks are the same person. I would have come up with something totally different if I wanted to hide something. The truth of the matter is that my cable provider changed our email address destinations (.com instead of .net) and one wasn't working for a time on edmunds for some reason, so I signed up on another name. You will see that one of the "names" hasn't been used in a long time. Not trying to hide a thing here.

However, I am nothing more than an owner of a 2011 Silverado 5.3 Crew Cab and not an employee.

I only respond to blanket generalizations or half truths by the 14 unhappy owners on this forum.

clint74 · February 2012

My 2007 silverado with same engine acts the same as yours. I also have had Honda Odyssey with this feature but it stayed in 3 cylinder (of 6) as long as you were under 80mpg, must have something to do with throttle percentage, but the Honda resulted in much better highway mpg gains and was more real world applicable, even when fully loaded with 6 large adults and luggage. I think GM could learn from the Honda engineers in regards to this feature.

chuck1 · February 2012

Don't know that's it's possible you can compare an almost 2 ton, body on frame vehicle with the aerodynamics of a refrigerator to a uni-body front wheel drive mini-van.

As it is - the trucks will get 20mpg (staying at 70 mph or below) with AFM on the highway. That's pretty good IMHO.

midasdog · February 2012

Like to see a Silverado with the 5.3 with that kind of milage. Mine has 125,000 miles and it has been 15.6mpg to 15.7mpg from the day it was new. Last one with 4.8 was like 18-19mpg

string2 · February 2012

Since your warranty has expired, why not get your computer fixed to work like it should. I'm tempted to myself, but I only have 5,700 miles on mine now. My average mpg right now is showing 14.7 mpg. I drive about 60% between 60 - 72.

z71silverado · March 2012

2007 Silverado Z71 with 5.3L Iron block and AFM. Just changed my plugs at 90K. Havent had one problem with my truck since day 1! Just ran out of warrant period as well. Plugs showed signs of wear on the cylinders that constantly run but the other plugs looked great! I drive conservatively and try to get it into V4 mode as much as possible. Even while towing itll enter V4 mode and has great power. I can say I do NOT have a problem with my AFM.

string2 · March 2012

You're Lucky!

chuck1 · March 2012

He is not lucky.

A better way to look at it is that GM sold almost a half million of these trucks last year, and most happy owners don't take the time to post that they are satisfied with their purchase decision.

lstrip · March 2012

So chucks,
those of us that do have afm issue are definitely UNLUCKY.
Yes it does appear to be a matter of luck if you get a vehicle that does not have this issue. No one on this forum has said that EVERY vehicle is defective but, there is enough evidence to validate the existance of a problem with the afm/6 speed combination. My dealer acknowledges this. When will you finally understand and acknowledge that these issues need to be addresses by gm.
Larry

chuck1919 · March 2012

"No one on this forum has said that EVERY vehicle is defective but, there is enough evidence to validate the existance of a problem with the afm/6 speed combination"
.
If you call 14 guys ON THIS BOARD out of a half-million units "evidence" then that's YOUR perspective.

string2 · March 2012

Many GM truck owners use there truck for heavy duty working and may not be that interested in when V8 stops and V4 kicks in. I'll bet many, if not most, GM buyers don't even know about this website. Besides, there are many other sites that may have been posted to. There aren't 500,000 GM owner's with AFM engines that have posted on this website in the past few years. Fourteen complaints on just one website (from those who took the time to do it) seems like it might be a pretty good representative sample of a bunch of people who are not happy campers!

chuck1919 · March 2012

14 out of 500,000=.000002%

Just saying.

string2 · March 2012

14 out of 500,000=.000002% Just saying.

===============================================
You're somewhat of a "Spin Doctor"

A more realistic calculation would be:
14 "AFM" complaints out of the number of positive "AFM" posts from new truck owners who actually visited this website. (Apples & Apples)
If you found the complaints, you can find the positive posts and easily do the math!

chuck1919 · March 2012

People who are happy with their purchase(s) often do not post.

lstrip · March 2012

chucks is PAID to spin!!

string2 · March 2012

chucks is PAID to spin!!

=================================================

He's gonna spin himself right out of a job if he keeps up with his phony facts!

chuck1 · March 2012

I am not a GM employee nor am I paid by anybody to post here. If you look at my number of posts I have been around for a long time on various boards.

alstairs · April 2012

I just bought a 2012 Silverado Crew LTZ two weeks ago. I absolutely love the truck. I have noticed something happening with the fuel economy though. (That's why I'm searching the net...)

I've been playing around with the truck in different 4X4 modes, and it seems like in 4 wheel drive the AFM actually comes on more often at highway speeds. Has anyone ever tried that and got similar results? I drive the same route daily, so one day in 2WD, one day in 4WD. I did see a difference.

I plan on taking it to the local dealer, just haven't had a chance.

Like others, I expect to get what I purchased. if a vehicle claims to get a certain MPG, I would hope to at least get close to that. I also agree with Chuck, in general, those that are happy or don't notice issues will not spend the time to post.

donl1 · April 2012

I don't understand why you're running around in 4 wheel drive on the dry...unless this is your first 4x4 vehicle. :confuse:

alstairs · April 2012

I'm just did it in a small period of time to see if there was a difference in mileage..and there was. Only, I expected it to be worse in 4WD, not better. Now I am wondering if it is a programming error within the AFM side of things. If someone could explain to me why the 4Cyl mode was active more when I was in 4WD I would love to hear why. It sort of baffles me.

gmcustsvcsarah · April 2012

Good morning alstairs,

Looking forward to an update on how your dealership visit goes when you get the chance.

All the best,
Sarah
GM Customer Service

kalen3 · April 2012

I JUST BOUTH THIS TRUCK USED AND IT IS POWER SURGING IM NOT SURE WHAT IT IS BUT ITS ANOYING AND REALLY MAKING MY QUESTION MY DESION IT HAS A 5.3 Z71

alstairs · April 2012

Hi Sarah. I did take it to a dealer. Even with me explaining fully the issue, they came back with "The AFM is coming on". I knew it was coming on. My issue was it wasn't coming on very often. Also, they said they didn't see any bulletins. (Maybe I'm the first to complain??)
After +1300KM, it appears to be a little better on the highway. Still not near the rates posted when I bought it though. I honestly wish someone who designed this system would take a second look and see if this could be improved. Gas isn't getting any cheaper. I just don't know how to get that level within GM involved.

string2 · April 2012

Hi Alstairs,
Hi Sarah. I did take it to a dealer. Even with me explaining fully the issue, they came back with "The AFM is coming on". I knew it was coming on. My issue was it wasn't coming on very often. Also, they said they didn't see any bulletins. (Maybe I'm the first to complain??)
After +1300KM, it appears to be a little better on the highway. Still not near the rates posted when I bought it though. I honestly wish someone who designed this system would take a second look and see if this could be improved. Gas isn't getting any cheaper. I just don't know how to get that level within GM involved.
====================================================

You're not the only one with this same problem. Just read back at some of the other posts, including mine.
You can forget about GM fixing the problem. For some reason if the AFM is not working at steady highway speed, it is designed to NOT trip a trouble code. Problem is, if they can't detect that trouble code, they don't see a problem and they don't know where to start looking. However, mine did show a problem ( at about 65 MPH ) with the MAP on their Tech 2 diagnostic tool , but GM told the Dealer service man "that was normal". That seemed strange to me because the dealer service mgr, who checks these trucks every day, didn't know what to make of it and called GM to see how to handle the problem.
It seems no matter what the problem is with the AFM, they say it is normal!

Maybe if enough people complain about GM's AFM problem, they will make some effort to correct it. It's probably in their ECM computer programing.
Mine is a 2011 Chevy Silverado Crew Cab 1/2 ton, 5.3, 6 speed automatic. Has about 8,000 miles on it. Has the same problem since bought new. I get 16 MPG on level highway, 15 MPG in town (they tell me that's normal)

Good Luck with yours!

Chevy Silverado and GMC Sierra Active Fuel Management Problems

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