GM Truck Club Forum banner

1 - 20 of 32 Posts

·
Registered
Joined
·
9 Posts
Discussion Starter · #1 ·
Hi All,

My 2012 Silverado has been having some issues with the AFM feature.

When I am driving at highway speeds (55-60mph) the truck will move to V4 and stay there for a few minutes. While staying at the same speed it will shift back into V8, even if I'm on cruise. I would think unless I'm on a slight incline I'd primarily stay in V4.

Why would be constantly be switching back and forth? Not to mention the annoying sound of the V4. It honestly sounds like the transmission is struggling and making a rumble sound.

Appreciate any feedback or assistance.
 

·
Premium Member
Joined
·
6,542 Posts
When dealing with the AFM feature my recomendation for the easiest fix would be to buy a Range AFM delete module.
It's plug and play and from experience I can tell you it'll only affect MPG by less than a full mile per gallon.
Stops that annoying shift between 4 and 8 cyl, and reduces chance of atm system failure later on.
Look on Amazon and you should be able to find a module for less than $200
 

·
Registered
Joined
·
15,237 Posts
As you know, the shift into V4 and out of V4 is caused by the Powertrain Control Module, the PCM, the "computer".
It has a set of parameters that when matched, commands the V4 shift. While in this mode, the computer now monitors the engines vitals, when it see the block temps starting to change (cylinders that are shut off, don't produce heat), it commands the V8 mode.

Switching back and forth is normal.
 

·
Registered
Joined
·
9 Posts
Discussion Starter · #4 ·
The problem I feel is how quickly it keeps shifting between the two. It will shift down into v4 for a minute or two and then back to v8 and repeat, repeat, repeat.
 

·
Registered
Joined
·
1,578 Posts
Theres a lot going on in there

The engine control module (ECM) is responsible for the management and control of all engine functions. Each ECM comes equipped with a specific set of software/calibrations designed for that engine and vehicle application. The ECM will determine engine operating parameters, based upon information from a network of switches, sensors, modules and communication with other controllers located throughout vehicle. Internal to the ECM is an integrated circuit device called a low-side driver. The low-side driver is designed to operate internally, like an electronic switch. An individual low-side driver controls eachvalve lifter oil manifold (VLOM) solenoid. When enabling conditions for V4 mode are met, the ECM will command the low-side driver to ground each VLOM solenoid control circuit, in firing order sequence. Internal to the low-side driver is a fault detection circuit, which monitors the solenoid control circuit for an incorrect voltage level. If an incorrect voltage level, such as an open, high resistance, or short to ground, is detected, the low-side driver, along with the fault detection circuit, will communicate the condition to the central processor in the ECM. The ECM will then command a return to V8 mode, set a corresponding DTC, and illuminate the malfunction indicator lamp (MIL) on the instrument panel.

Cylinder Deactivation Inhibit Reasons
Listed below are the powertrain conditions that will inhibit V4 mode, while operating under light load driving conditions:

• Engine manifold vacuum low

Brake booster vacuum pressure low

• Accelerator pedal position rate of increase too high, electronic throttle control

• Accelerator pedal position too high, electronic throttle control

• Ignition voltage out of range

• Engine oil pressure out of range

• Engine oil temperature out of range

• Engine RPM out of range

Transmission gear incorrect

• Transmission range incorrect

• Transmission gear shift in progress

• All cylinders activated via scan tool output control

• Minimum time in V8 mode not met

• Maximum V4 mode time exceeded

• Engine oil aeration present

• Decel fuel cutoff active

• Fuel shut-off timer active

• Minimum heater temp low, HVAC system

• Reduced engine power active, electronic throttle control

• Brake torque management active

• Axle torque limiting active

• Engine metal over temperature protection active

Catalytic converter over temperature protection active

• Piston protection active, knock detected

• Hot coolant mode active

• Engine over speed protection active

• Fault Active or Fault Pending--cylinder deactivation is disabled for the following faults:

- Brake BoosterVacuum Sensor

- Manifold Absolute Pressure Sensor

- Engine Oil Pressure Sensor

- Engine Coolant Temperature Sensor

- Vehicle Speed Sensor

- Crankshaft Position Sensor

- Engine Misfire Detected

- Cylinder Deactivation Solenoid Driver Circuit
 

·
Registered
Joined
·
61 Posts
Wow that is a lot of variables. I like the idea of not having it in the first place. It seems like to me that it would waste more fuel than actually help out. Constantly switching from V8 toV4 just seems like it would use more fuel than if it just stayed in one form or the other. But then again to me mine seems to stay in V8 mode more than V4.
 

·
Registered
Joined
·
3,573 Posts
WOW that is a lot of crap to go wrong eh! ctrl alt delete...

what do you think Squatchy is the best solution for these motors... the full afm delete kit and ecm reflashed or the range technology?
 

·
Registered
Joined
·
1,578 Posts
Range for the cheap guys, good tune for the average guys, full delete you are definitely getting into some money, ya gotta figure a small percentage would be willing to take apart their top end, tho an afm delete kit is only $400 give or take. When you are going that far theres no point (imo) to not go with a cam upgrade, something like a tsp 224r cam is gonna run another $400, you'd need a tune on top of that, $3-600 ballpark there. I was actually in the process of figuring out what all I wanted to do with my half ton, afm delete cam headers machined heads supercharger 3200 stall converter 4.11 gears, adding up all the cost and I just kinda said that's just stupid, I'll buy a duramax and be money and power ahead. I would recommend custom tune personally, if nothing else just having the trans tuned is so much better. You'd be hard pressed to have trouble with a dealership because of a tune. I was lifted and tuned and had warranty work done on mine.
 

·
Registered
Joined
·
3,573 Posts
that all makes sense to me. A good buddy of mine has an 09 sierra, reg cab, short box, I believe, a very nice truck but hes got that motor. he just wont quite listen to me about this potential future problem, hes got about 160 000 km without any engine work, at least what he can tell. hes had it for about a year... time will tell. he falls into the cheap catagory, iv told him about the range tech and how its only $200... but no... he wont even look it up.
 

·
Registered
Joined
·
15,237 Posts
Al, keep in mind, they don't all break. It's actually a small percentage.

We only hear about the ones that break, so it seems high.
 

·
Registered
Joined
·
3,573 Posts
thats what I'm hoping Ray!
 

·
Registered
Joined
·
5,200 Posts
Just about any tuner (I use Diablosport inTune 2) will turn off AFM. I'm in the East Texas hills and my truck was constantly switching back and forth. With any of the canned tunes and AFM turned off I didn't notice a hit on mpg. If anything I gained a mile or two. On the flats toward the coast I gained even more.

I would also recommend an oil catch can. It will knock out most of the oil vapors that get to the cylinders and potentially cause a stuck ring and/or cylinder glazing, not to mention dirty intake tube and throttle body.

Ted
 
  • Like
Reactions: thegawd

·
Registered
Joined
·
714 Posts
Why would be constantly be switching back and forth? Not to mention the annoying sound of the V4. It honestly sounds like the transmission is struggling and making a rumble sound. Appreciate any feedback or assistance.
I drive a lot on I-95 in Florida and most of the road is level with my 2012 Silverado with tow package. Bridge over passes are about the only hill climb. For one even at 70MPH the engine will switch back and forth from V8 to V4. While towing on the down side of the bridge it will switch to V4 mode. But I never had any indication of a sound change and never felt anything when the AFM is doing it's job. Your indication of a change may be another issue but the constant V4 to V8 mode is quite normal.

With government MPG requirements getting tighter and tighter, I think GM AFM feature might only increase MPG by less than 1%, and that could be quite a lot of an improvement for V8's for the money invested by engineering. Ford has started increasing 4 and 6 cylinders offers with turbos to get the horsepower & EPA requirements needed, and the latest F150 main engine is the V6 turbo but GM truck buyers just love the V8 engines. GM trucks will have to go on a big diet and V6 will be the mainstay to meet future MPG ratings and buyers will not have to pay gas guzzler tax. Now there is a new EPA requirement for ALL vehicles, the GHG (Greenhouse Gas) emissions. I think AFM will be around for quite a while.

https://www3.epa.gov/otaq/climate/documents/420f12051.pdf
https://www3.epa.gov/otaq/climate/regs-light-duty.htm
https://www3.epa.gov/fueleconomy/guzzler/420b16052.pdf
 

·
Registered
Joined
·
61 Posts
It is really weird when it does switch over to V4, just makes you feel like it is hesitating. Almost like there is a problem when there isn't.
 

·
Registered
Joined
·
1,578 Posts
I drive a lot on I-95 in Florida and most of the road is level with my 2012 Silverado with tow package. Bridge over passes are about the only hill climb. For one even at 70MPH the engine will switch back and forth from V8 to V4. While towing on the down side of the bridge it will switch to V4 mode. But I never had any indication of a sound change and never felt anything when the AFM is doing it's job. Your indication of a change may be another issue but the constant V4 to V8 mode is quite normal.

With government MPG requirements getting tighter and tighter, I think GM AFM feature might only increase MPG by less than 1%, and that could be quite a lot of an improvement for V8's for the money invested by engineering. Ford has started increasing 4 and 6 cylinders offers with turbos to get the horsepower & EPA requirements needed, and the latest F150 main engine is the V6 turbo but GM truck buyers just love the V8 engines. GM trucks will have to go on a big diet and V6 will be the mainstay to meet future MPG ratings and buyers will not have to pay gas guzzler tax. Now there is a new EPA requirement for ALL vehicles, the GHG (Greenhouse Gas) emissions. I think AFM will be around for quite a while.

https://www3.epa.gov/otaq/climate/documents/420f12051.pdf
https://www3.epa.gov/otaq/climate/regs-light-duty.htm
https://www3.epa.gov/fueleconomy/guzzler/420b16052.pdf
Afm is reported to increase mileage by 5.5-7.5% in "perfect world" conditions. I've yet to see anybody say their mileage went down after having it tuned out tho.
 

·
Registered
Joined
·
5,200 Posts
Most drivers who tune it off, whether via a professional tuner or an OBD11 tuner, also load a remapping tune for either economy or performance. The tune is more than enough to overcome any loss of AFM's supposed economy. The Range module is the only one I know of offhand that will lock out AFM leaving all other engine and transmission parameters untouched.

The 6L80E is foremost an economy enhancing transmission. Gears 5 and 6 are overdriven. If placed in manual mode 5 it will lock out AFM. As a test you can use this M5 as a AFM lockout to compare with the V8 - V4 - V8 switching in 6th. This is a good test to run in town in traffic. If you haven't yet tuned off AFM try it. It might surprise you when there's so little change in mpg.

Ted
 

·
Registered
Joined
·
15,237 Posts
Ted, I use M5 all the time and it keeps mine from going into V4; however, I've heard it no longer does it on the newer trucks (I'm going to say '10 and up). In fact, on the '13 and up trucks, the V4 mode will kick in at idle.
 

·
Registered
Joined
·
3,573 Posts
this m5 you speak of... is it on all afm trucks? it might be an idea for my buddies truck....
 

·
Registered
Joined
·
15,237 Posts
this m5 you speak of... is it on all afm trucks? it might be an idea for my buddies truck....
Hey Al, how are ya?
M5 = manual selected 5th gear.
The 6 speed transmission has a manual selection.
The dash display has PRNDM
The gear select lever has a paddle shifter to select the gear (if I select 5, the transmission shifts normally up and down between 1 and 5, but will not shift into 6.
You don't need to be in Tow/Haul.
 
1 - 20 of 32 Posts
Top